G3500 Industrial Engines Caterpillar

Detonation Retard and Detonation Shutdown

Usage:

System Operation Description:

The Timing Control Module (TCM) will take action in order to help protect the engine from detonation. The TCM will attempt to stop the detonation by retarding the ignition timing. If this effort is unsuccessful and the detonation continues at severe levels, the TCM will signal for an engine shutdown.

The detonation sensors provide an electrical signal of the mechanical engine vibrations to the TCM. The TCM monitors the detonation sensors in order to determine the severity of the detonation.

The detonation protection is disabled for engine speeds that are less than 500 rpm. Detonation protection is enabled ten seconds after the engine reaches 500 rpm.

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Illustration 1	g00664930
Typical display of menu 2 and screen 12 on the DDT Three bars of detonation are shown.

The retardation of timing is the first level of protection against detonation. If the engine detonation is greater than five bars, the TCM retards the ignition timing by six degrees. The control begins checking the detonation for a possible shutdown after the TCM has retarded the timing. There are two strategies for a shutdown due to detonation. One strategy is for non-gallery cooled pistons. The second strategy is for gallery cooled pistons.

For non-gallery cooled pistons, a shutdown will be activated if detonation exceeds six bars within five seconds after the engine has been retarded. A shutdown will also be activated if detonation is in the range of five to six bars after the five seconds.

For gallery cooled pistons, detonation is not checked for the first six seconds after the timing is retarded. A shutdown will be activated only if both of the following conditions are true:

The detonation level is in the range of five to six bars.
The engine has been retarded for six seconds.

As the detonation level decreases, the TCM will begin to advance the timing out of the detonation retarded timing. The maximum rate of advance is one degree per minute. This rate is achieved for detonation levels of two to three bars. If the detonation level increases to a level of four to five bars, the rate of the advance will decrease or the advance will stop.

While the ignition timing is retarded due to detonation, the yellow "DETONATION RETARDED TIMING" LED will be illuminated.

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Illustration 2	g00664929

Not all of the Test Steps for determining the cause of detonation follow a linear sequence. The results of the steps determine the sequence of the steps. Illustrations 3 through 8 constitute a flow chart of the Test Steps. Use the Illustrations only for reference. To determine the cause of detonation, use the more detailed instructions that are included in the Test Steps which follow the Illustrations.

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Illustration 3	g00698785

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Illustration 4	g00698786

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Illustration 5	g00698788

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Illustration 6	g00698791

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Illustration 7	g00698793

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Illustration 8	g00698801

Test Step 1. Check the Timing.

Note: The desired timing will vary for different engine applications.

Use the DDT to check the engine timing. For the correct desired timing for the engine application, see Systems Operation/Testing and Adjusting, SENR4604, "Ignition System".

Expected Result:

The desired timing is correct.

Results:

OK - The timing is correct for the engine application. Proceed to test step 2.
Not OK - Detonation occurs because the timing is not correct for the engine application.
Repair: Use the DDT to set the proper timing.
Stop.

Test Step 2. Check the Air/Fuel Ratio.

Note: The air/fuel ratio will vary for different engine applications. The inlet manifold air temperature will affect the air/fuel ratio.

Verify that the engine is operating with the correct air/fuel ratio. Refer to Systems Operation/Testing and Adjusting, SENR4604, "Fuel System".

Expected Result:

The engine is operating with the correct air/fuel ratio.

Results:

OK - The air/fuel ratio is correct. Proceed to test step 3.
Not OK - The detonation is caused by an incorrect air/fuel ratio.
Repair: Correct the air/fuel ratio according to Systems Operation/Testing and Adjusting, SENR4604, "Fuel System".
Stop.

Test Step 3. Check the Inlet Manifold Air Temperature.

Note: The inlet manifold air temperature will affect the air/fuel ratio. The inlet manifold air temperature will vary for different ratings of water temperature regulators (aftercooler).

Verify that the engine is operating with the correct inlet manifold air temperature. Refer to Systems Operation/Testing and Adjusting, SENR4604, "Inlet Manifold Air Temperature".

Expected Result:

The inlet manifold air temperature is acceptable for the engine.

Results:

OK - Proceed to test step 4.
Not OK - The detonation is caused by an incorrect inlet manifold air temperature.
Repair: Correct the inlet manifold air temperature according to Systems Operation/Testing and Adjusting, SENR4604, "Inlet Manifold Air Temperature".
Stop.

Test Step 4. Check the Detonation Sensors.

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Illustration 9	g00664778
Detonation sensor (1) Buffer module (2) Accelerometer

Verify that the sensors are mounted properly onto the engine block.

Inspect the wire between the accelerometer and the buffer module for corrosion and damage.

Expected Result:

The sensors are mounted properly. The wiring is free of corrosion and damage.

Results:

OK - The sensors appear to be good. Proceed to test step 5.
Not OK - The sensor is not mounted correctly or there is a problem in the wiring.
Repair: If a sensor is damaged, replace the sensor. Use 10 N·m (7.4 lb ft) of torque to secure the accelerometers into the engine block.
Stop.

Test Step 5. Check the Wires of the Accelerometers.

Start the engine. Use the DDT to monitor the level of detonation.

Wiggle the wires of the accelerometers while you monitor the level of detonation.

Expected Result:

The level of detonation does not change.

Results:

OK - The wires of the accelerometers are in good condition. Proceed to test step 6.
Not OK - The wiring for the accelerometers is damaged.
Repair: Replace the detonation sensor.
Stop.

Test Step 6. Check the Engine Harness Wires

Start the engine. Use the DDT to monitor the level of detonation.

Monitor the level of detonation while you wiggle the wires for the detonation sensors at the ends of the engine harness. When possible, wiggle the wires for the detonation sensors throughout the engine harness.

Expected Result:

The level of detonation does not change.

Results:

OK - The wires for the detonation sensors are in good condition throughout the engine harness. Proceed to test step 10.
Not OK - There is a problem with the wiring for the detonation sensors in the engine harness. Proceed to test step 7.

Test Step 7. Check the Connectors of the Timing Control Module for Damage

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There is a strong electrical shock hazard unless the system power is disconnected.

Remove power from the control system. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker in the engine mounted junction box.

Inspect the connection for the Timing Control Module (TCM). Inspect the connections for the detonation sensors. Look for corrosion and damage. Refer to Troubleshooting, "Inspecting Electrical Connectors".

Expected Result:

The connectors are in good condition. The connections are secure.

Results:

OK - Proceed to test step 8.
Not OK - The connectors are corroded and/or damaged. The connections are not secure.
Repair: Repair the faulty connector or replace the harness.
Stop.

Test Step 8. Check the Engine Harness for Short Circuits

Disconnect the Timing Control Module (TCM) and the detonation sensors from the engine harness.

For the right and left sensors, use the multimeter with the 40,000 ohm scale. Measure the resistance at the Timing Control Harness Connector (TCHC) between the points that are listed in Table 1:

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Table 1
Resistance Check for the Right and Left Detonation Sensors Timing Control Harness Connector (TCHC)
Pin E	Pin A
	Pin D
	Pin I
	Pin J
	Pin F
	Pin B
	Pin M
	Pin N
	Housing of the connector

For the right and left sensors, use the multimeter with the 40,000 ohm scale. Measure the resistance at the TCHC between the points that are listed in Table 2:

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Table 2
Resistance Check for the Right and Left Detonation Sensors Timing Control Harness Connector (TCHC)
Pin F	Pin B
	Pin E
	Pin J
	Pin K
	Pin G
	Pin C
	Pin M
	Housing of the connector

For the right sensor, use the multimeter with the 40,000 ohm scale. Measure the resistance at the TCHC between the points that are listed in Table 3:

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Table 3
Resistance Check for the Right Detonation Sensor Timing Control Harness Connector (TCHC)
Pin J	Pin E
	Pin I
	Pin O
	Pin P
	Pin K
	Pin F
	Pin M
	Pin N
	Housing of the connector

For the left sensor, use the multimeter with the 40,000 ohm scale. Measure the resistance at the TCHC between the points that are listed in Table 4:

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Table 4
Resistance Check for the Left Detonation Sensor Timing Control Harness Connector (TCHC)
Pin K	Pin F
	Pin J
	Pin P
	Pin R
	Pin L
	Pin G
	Pin M
	Pin N
	Housing of the connector

Use the multimeter with the 40,000 ohm scale. Measure the resistance in the junction box between each terminal for the wires of the detonation sensors and the adjacent terminals.

Expected Result:

All of the readings are greater than 2000 ohms.

Results:

OK - No shorts were found to the -battery, the +battery, a sensor ground, or adjacent pins. Proceed to test step 9.
Not OK - There is a problem in the wiring harness. There is a short to the -battery, the +battery, a sensor ground, or an adjacent pin.
Repair: Repair the faulty connector or replace the harness.
Stop.

Test Step 9. Check the Harness of the Timing Control Module for Open Circuits

Set the multimeter to the 400 ohm scale. Check the continuity in the engine harness between the points that are listed in Table 5:

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Table 5
Points to Check for Continuity in the Harness
Timing Control Harness Connector (TCHC)	Right Detonation Sensor
Pin E	Pin A
Pin F	Pin B
Pin J	Pin C
Timing Control Harness Connector (TCHC)	Left Detonation Sensor
Pin E	Pin A
Pin F	Pin B
Pin K	Pin C

Expected Result:

All of the readings are less than 2 ohms.

Results:

OK - The harness does not have an open circuit. The cause is undetermined or the problem is intermittent.
Repair: Reset the system and troubleshoot any active diagnostic codes.
Stop.
Not OK - The harness has open circuits.
Repair: Repair the faulty connector or replace the harness.
Stop.

Test Step 10. Adjust the Timing.

Operate the engine at full load or under the conditions that cause the problem. Note the level of detonation.

Note the original ignition timing. Then retard the ignition timing by three to six degrees. Check for a change in the level of detonation.

Expected Result:

The level of detonation decreases.

Results:

OK - Retarding the timing causes the level of detonation to decrease. Proceed to test step 11.
Not OK - Retarding the timing does not change the level of detonation. Proceed to test step 15.
Not OK - Retarding the timing causes the level of detonation to increase. Proceed to test step 14.

Test Step 11. Richen the Air/Fuel Mixture

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NOTICE

If the air/fuel mixture is too rich, detonation will occur. To help prevent damage to the engine, do not richen the air/fuel mixture by a large amount. Do not allow the engine to detonate excessively.

Adjust the ignition timing to the original setting.

Use the DDT to monitor the level of detonation. Slightly richen the air/fuel mixture.

Expected Result:

When the air/fuel mixture is slightly richened, the level of detonation increases.

Results:

Yes - Richening the air/fuel mixture increases the level of detonation. The cause is actual detonation. Proceed to test step 12.
No - Richening the air/fuel mixture does not affect the level of detonation, or there is slightly less detonation.
Repair: The cause of the detonation is undetermined. Reset the system and troubleshoot any active diagnostic codes.
Stop.

Test Step 12. Measure the Cylinder Pressure

Note: An accumulation of deposits can cause detonation. Applications that use landfill gas are more prone to deposits.

Measure the cylinder pressure. For typical cylinder pressures, see the Operation and Maintenance Manual, SEBU6355, "Cylinder Pressure" topic.

Expected Result:

The compression ratio is within specifications.

Results:

OK - The cylinder pressure is acceptable. The detonation is not due to deposits. Proceed to test step 13.
Not OK - The cylinder pressure has risen by one or more compression ratios.
Repair: The engine needs a top end overhaul in order to remove the deposits. For information, see Operation and Maintenance Manual, SEBU6355, "Top End Overhaul Instructions".
Stop.

Test Step 13. Check the Methane Number of the Fuel

Obtain a fuel analysis of the gas.

Enter the data from the fuel analysis into the Caterpillar Software Program, LEKQ6378, "Methane Number Program".
The software calculates the fuel's methane number.

Compare the methane number to the recommendation from the appropriate Engine Performance, "Fuel Usage Guide".
For generator set engines, see Engine Performance, LEBQ6169.
For industrial engines, see Engine Performance, LEBQ6117.

Expected Result:

The methane number of the fuel is compatible with the engine.

Results:

OK - The cause of detonation is undetermined. Reset the system and troubleshoot any active diagnostic codes.
Not OK - The methane number of the fuel is incorrect for the engine.
Repair: Obtain the proper fuel or adjust the settings of the engine in order to accommodate the methane number of the fuel that is being used.
Stop.

Test Step 14. Richen the Air/Fuel Mixture

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NOTICE

If the air/fuel mixture is too rich, detonation will occur. To help prevent damage to the engine, do not richen the air/fuel mixture by a large amount. Do not allow the engine to detonate excessively.

Adjust the ignition timing to the original setting.

Use the DDT to monitor the level of detonation. Slightly richen the air/fuel mixture.

Expected Result:

When the air/fuel mixture is slightly richened, the level of detonation decreases.

Results:

YES - Richening the air/fuel mixture decreases the level of detonation. The cause is related to ignition system noise. Proceed to test step 23.
NO - Richening the air/fuel mixture does not affect the level of detonation, or there is slightly more detonation.
Repair: The cause of the detonation is undetermined. Reset the system and troubleshoot any active diagnostic codes.
Stop.

Test Step 15. Reduce the Load

Use the DDT to monitor the level of detonation. Slowly reduce the load until there is no load on the engine.

Expected Result:

When the load is removed, the level of detonation decreases.

Results:

OK - Reducing the load decreases the level of detonation. Proceed to test step 16.
Not OK - Reducing the load does not affect the level of detonation. Proceed to test step 17.

Test Step 16. Check for Pre-Ignition

A hot spot in the combustion chamber is usually the cause of pre-ignition. The following circumstances are possible sources of pre-ignition:

A spark plug is incorrect for the application.
Improper installation of spark plugs. For example, the torque might be incorrect.
A foreign object is attached to a piston, the head, a valve, a spark plug, etc.

Expected Result:

No source of pre-ignition is found.

Results:

OK - The detonation is not caused by a condition of pre-ignition. Proceed to test step 17.
Not OK - A source of pre-ignition is found.
Repair: Correct the cause of the pre-ignition.
Stop.

Test Step 17. Isolate the Detonation Sensors

Shut OFF the engine. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker for the fuse in the junction box.

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NOTICE

Disconnecting the shutdown output of the Timing Control Module (TCM) will disable the detonation shutdown protection. Do not allow the engine to detonate excessively.

Disconnect pin "P" for the Timing Control Module (TCM) from the terminal strip in the junction box. This will disconnect the shutdown output of the TCM.

Remove the buffer modules for the detonation sensors from the engine block. This will help to prevent twisting of the wires for the accelerometers. Remove the accelerometers from the engine block.

Reinstall the buffer modules onto the engine block.

Reconnect the detonation sensors to the engine harness. Allow the accelerometers to hang so that the accelerometers do not contact the engine block.

Close the circuit breaker for the fuse in the junction box.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively.

Expected Result:

The level of detonation decreases.

Results:

OK - The isolation of the detonation sensors reduces the level of detonation. Proceed to test step 18.
Not OK - The isolation of the detonation sensors does not change the level of detonation or an increase occurs. The problem is due to electrical noise in the engine harness. Proceed to test step 62.

Test Step 18. Wire Each Accelerometer to the Engine Block.

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NOTICE

During this test, there is no protection from detonation. Do not allow the engine to detonate excessively.

Turn OFF the engine. Use wiring to connect one of the accelerometers to the engine block.
Use wiring with a length of approximately 0.3 m (1 ft). Use wiring with lug connectors at both ends. Use a bolt to attach one end of the wire to the engine block in the threaded hole for the accelerometer. Use a nut to attach the other end of the wire to the stud of the accelerometer.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Disconnect the wire from the engine block and from the accelerometer. Attach the wire to the other accelerometer and to the engine block.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Expected Result:

The level of detonation does not change or the level is reduced.

Results:

OK - The level of detonation did not change or the level decreased. The problem is caused by mechanical noise. Proceed to test step 19.
Not OK - The level of detonation increases for either sensor. The problem is caused by general electrical noise in the engine block. Proceed to test step 40.
Not OK - The level of detonation increases with only one of the sensors. Proceed to test step 20.

Test Step 19. Install Each Sensor Separately

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NOTICE

During this test, there is no protection from detonation. Do not allow the engine to detonate excessively.

Turn OFF the engine. Install only the right accelerometer. Allow the left accelerometer to hang so that the accelerometer does not contact the engine block.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Remove the right accelerometer from the engine block. Install the left accelerometer. Allow the right accelerometer to hang so that the accelerometer does not contact the engine block.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Expected Result:

The level of detonation increases for only one of the sensors.

Results:

OK - The level of detonation increases for only the right sensor or the left sensor. Proceed to test step 20.
Not OK - The level of detonation increases for either sensor. The problem is general mechanical noise. Proceed to test step 22.

Test Step 20. Exchange the Detonation Sensors

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NOTICE

During this test, there is no protection from detonation. Do not allow the engine to detonate excessively.

Turn OFF the engine. Install the right detonation sensor into the position for the left detonation sensor. Install the left detonation sensor into the position for the right detonation sensor. However, allow the left accelerometer to hang so that the accelerometer does not contact the engine block. Attach both sensors to the engine harness.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Remove the right accelerometer from the engine block. Allow the right accelerometer to hang so that the accelerometer does not contact the engine block. Install the left accelerometer.

Start the engine. Use the DDT to monitor the operation for detonation. Operate the engine at full load. Observe the DDT for a change in the level of detonation. Do not allow the engine to detonate excessively. Stop the engine.

Expected Result:

The level of detonation increases for only one of the sensors when the sensor is installed in either bank.

Results:

Yes - The level of detonation increases for a particular sensor regardless of the bank. The sensor has failed.
Repair: Replace the sensor.
Stop.
No - The level of detonation increases for both of the sensors when either sensor is installed in a particular bank. If test step 19 was performed, proceed to test step 21. If test step 19 was not performed, proceed to test step 51.

Test Step 21. Investigate the Mechanical Vibrations for One Bank

The mechanical vibrations may be caused by one of the following conditions. However, other conditions and components may also be the cause of the noise.

The valve lash is incorrect.
The valve bridge requires adjustment.
The valves do not close properly.
The camshaft lobes and/or camshaft followers have nicks and/or scratches.
Components such as lines and brackets are not securely fastened.
Excessive piston slap

Investigate the source of the mechanical vibrations.

Expected Result:

The source of the mechanical vibrations is determined.

Results:

OK - A reason for the vibrations is found.
Repair: Correct the cause of the mechanical vibrations.
Stop.

Test Step 22. Investigate General Mechanical Vibrations

The mechanical vibrations may be caused by one of the following conditions. However, other conditions and components may also be the cause of the noise.

The drive coupling is worn.
The valve lash is incorrect.
The valve bridge requires adjustment.
Components such as lines and brackets are not securely fastened.
The engine mounts or the mounts for the driven equipment are loose.
The engine and the driven equipment are not aligned properly.
The bearings of the engine and/or the driven equipment are worn.
Excessive piston slap

Investigate the source of the mechanical vibrations.

Expected Result:

The source of the mechanical vibrations is determined.

Results:

OK - A reason for the vibrations is found.
Repair: Correct the cause of the mechanical vibrations.
Stop.

Test Step 23. Check the Ground Connection for the Magneto

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There is a strong electrical shock hazard unless the system power is disconnected.

Remove power from the control system. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker in the engine mounted junction box.

Inspect the ground wire to the magneto for loose connections and frayed wire.

Set the multimeter to the 400 ohm scale and measure the resistance between the housing of the magneto and the engine block.

Expected Result:

The resistance is less than 2 ohms.

Results:

OK - The ground connection for the magneto is good. Proceed to test step 24.
Not OK - The ground connection for the magneto is poor.
Repair: Repair the ground wire or replace the wire, if necessary.
Proceed to test step 24.

Test Step 24. Check the Ground Connections for the Ignition Transformers

Set the multimeter to the 400 ohm scale and measure the resistance between the flange of each ignition transformer and the engine block.

Expected Result:

The resistance for each ignition transformer is less than two ohms.

Results:

OK - The ground connections for the ignition transformers are good. Proceed to test step 25.
Not OK - The ground connection for the ignition transformer and the engine block is poor.
Repair: Clean the transformer and/or the valve cover. Replace the components, if necessary.
Proceed to test step 25.

Test Step 25. Check the Secondary Connections for the Ignition Transformers and Check the Extensions.

Remove the ignition transformers and the extensions.

Inspect the secondary connections of the ignition transformers for corrosion and buildup of deposits.

Set the multimeter to the 400 ohm scale and measure the resistance of each extension.

Inspect the connections of the extensions for corrosion and buildup of deposits. Look for pin holes that are caused by arcing.

Expected Result:

The resistance of each extension is less than 2 ohms. The secondary connections of the transformers and the extensions are in good, clean condition.

Results:

OK - The connections and the components are good. Proceed to test step 26.
Not OK - The secondary connections of the transformers and/or the extensions are dirty, corroded, or damaged.
Repair: Clean the components that are affected or replace the components, if necessary.
Proceed to test step 26.

Test Step 26. Check the Spark Plugs

Remove the spark plugs.

Set the multimeter to the 40,000 ohm scale and measure the resistance from the terminal of the spark plug to the center electrode. To ensure an accurate measurement, clean off deposits, if necessary.

Note: For inspection of spark plugs, see the engine's Operation and Maintenance Manual.

Verify that the ground electrode is not shorted to the center electrode. Verify that the spark plug gap is correct. Visually inspect the insulator of the spark plug for cracks.

Expected Result:

The resistance of each spark plug is less than 20,000 ohms. The spark plug gaps are within specifications. The spark plugs are in good, clean condition.

Results:

OK - The spark plugs are good. Proceed to test step 27.
Not OK - The resistance of the spark plugs is too high. The spark plugs are dirty and/or damaged. The spark plug gap is incorrect.
Repair: Clean the spark plugs or replace the spark plugs, if necessary. Set the spark plug gap to the correct specification.
Proceed to test step 27.

Test Step 27. Check for Detonation

Install the spark plugs, the extensions, and the ignition transformers.

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 28.

Test Step 28. Check the Engine's Ground Strap and Check the Battery Connections.

Verify that the following conditions exist for the engine's ground strap:
- The connections are secure.
- The connections are not corroded.
- The mating surfaces of the ground are free of paint.

Verify that the battery wiring is properly sized. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections for the battery are clean and secure.

Expected Result:

The engine's ground strap and the battery connections are secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The components are in good condition. Proceed to test step 29.
Not OK - The engine's ground strap and/or the battery connections are not in proper condition.
Repair: Repair the ground strap and/or the battery connections. Replace parts, if necessary.
Proceed to test step 29.

Test Step 29. Check the Earth Ground

Verify that the wiring for the earth ground is properly sized and free of corrosion. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections are free of paint, clean, and secure.

Set the multimeter to the 400 ohm scale. Measure the resistance between the engine block and the earth ground. An independent earth ground is preferred.

Expected Result:

The resistance is less than 2 ohms. The ground is secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The ground is good. Proceed to test step 30.
Not OK - The ground is not in proper condition.
Repair: Repair the ground. Replace parts, if necessary.
Proceed to test step 30.

Test Step 30. Check for Detonation

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 31.

Test Step 31. Check the Primary Connections of the Ignition System

Inspect the following connections for damage and/or corrosion: connections of the ignition transformers, connector for the ignition harness to the magneto and all connectors for the ignition harness. Refer to Troubleshooting, "Inspecting Electrical Connectors".

Expected Result:

All of the primary connections for the ignition system are in good condition.

Results:

OK - The connections are good. Proceed to test step 32.
Not OK - Parts of the primary connections for the ignition system are damaged and/or corroded.
Repair: Repair the connections or replace parts, if necessary.
Stop.

Test Step 32. Check the Ignition Harness for Short Circuits

Disconnect the ignition harness from the magneto. Disconnect all of the harness connectors from the ignition transformers. Refer to the engine's wiring diagram for the configuration of the wiring.

Set the multimeter to the 400,000 ohm scale. Check each pin of the connector for the magneto on the ignition harness. Check the connector for short circuits to the following points: +battery, -battery, engine block and all of the other pins on the connector.

Expected Result:

The resistance is greater than 400,000 ohms.

Results:

OK - The ignition harness is free of short circuits. Proceed to test step 33.
Not OK - The ignition harness has at least one short circuit.
Repair: Repair the wiring for the ignition harness and/or the connector. Replace parts, if necessary.
Stop.

Test Step 33. Check the Ignition Harness for Open Circuits.

Set the multimeter to the 400 ohm scale. Check the continuity for each pin of the connector for the magneto on the ignition harness. Check the pins to the corresponding pins of the connectors for the transformers and the junction box. Refer to the engine's wiring diagram for the configuration of the wiring.

Expected Result:

The resistance for each pin is less than 2 ohms.

Results:

OK - The ignition harness is free of open circuits. Proceed to test step 34.
Not OK - The ignition harness has at least one open circuit.
Repair: Repair the wiring for the ignition harness and/or the connectors. Replace parts, if necessary.
Stop.

Test Step 34. Substitute the Ignition Transformers

Note: This test step can be performed for one bank at a time.

Remove the original ignition transformers. Note the cylinder for each transformer.

Install different ignition transformers that are known to be good.

Operate the engine at full load or under the conditions that cause the problem. Note the level of detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine operation is normal. Proceed to test step 35.
Not OK - Detonation still occurs after both banks of transformers are substituted. Reinstall the original transformers. Then proceed to test step 36.

Test Step 35. Install the Original Ignition Transformers One At A Time.

Install one of the original ignition transformers.

Operate the engine at full load or under the conditions that cause the detonation. Note the level of detonation.

Expected Result:

Detonation does not occur.

Results:

OK - Detonation does not occur after installation of the original transformer. Repeat this test step until all of the original transformers are reinstalled.
Repair: If detonation does not occur after installation of the original transformers, one of the following conditions may have caused the detonation:
- The detonation is intermittent. The original transformers are in good condition.
- A poor primary connection or a poor secondary connection to a transformer was disturbed. This caused the detonation to cease.
- One or more of the original transformers fails intermittently.
Investigate these potential sources of the detonation. Correct the situation, if necessary.
Stop.
Not OK - Detonation recurs after the original transformer is installed. The transformer is faulty.
Repair: Replace the faulty transformer. Reinstall the original transformers one at a time. After each transformer is installed, operate the engine and monitor the operation for detonation. Replace any other transformers that are faulty.
Stop.

Test Step 36. Substitute the Magneto

Remove the original magneto. Install a magneto that is known to be good.

Operate the engine at full load or under the conditions that cause the detonation. Note the level of detonation.

Expected Result:

Detonation does not recur.

Results:

OK - Detonation does not recur after the magneto is substituted. Proceed to test step 37.
Not OK - Detonation recurs after the magneto is substituted. Reinstall the original magneto. Proceed to test step 38.

Test Step 37. Install the Original Magneto

Reinstall the original magneto.

Operate the engine at full load or under the conditions that cause the detonation. Note the level of detonation.

Expected Result:

The detonation recurs.

Results:

Yes - Detonation recurs after the original magneto is installed.
Repair: Replace the original magneto with a good magneto.
Stop.
No - Detonation does not recur after the original magneto is installed.
Repair: The detonation may be due to one of the following conditions:
- The detonation is intermittent. The original magneto is good.
- The original magneto fails intermittently.
Investigate these potential sources of the detonation. Correct the situation, if necessary.
Stop.

Test Step 38. Substitute the Timing Control Module

Remove the original Timing Control Module (TCM). Install a TCM that is known to be good.

Operate the engine at full load or under the conditions that cause the detonation. Note the level of detonation.

Expected Result:

Detonation does not recur.

Results:

OK - Detonation does not recur after the TCM has been substituted. Proceed to test step 39.
Not OK - Detonation recurs after the TCM has been substituted. The source of the detonation is undetermined.
Repair: Reinstall the original TCM. Reset the system and troubleshoot any active diagnostic codes.
Stop.

Test Step 39. Install the Original Timing Control Module

Reinstall the original Timing Control Module (TCM).

Operate the engine at full load or under the conditions that cause the detonation. Note the level of detonation.

Expected Result:

The detonation recurs.

Results:

Yes - Detonation recurs after the original TCM is installed.
Repair: Replace the original TCM with a good TCM.
Stop.
No - Detonation does not recur after the original TCM is installed.
Repair: The detonation may be due to one of the following conditions:
- The detonation is intermittent. The original TCM is good.
- The original TCM fails intermittently.
Investigate these potential sources of the detonation. Correct the situation, if necessary.
Stop.

Test Step 40. Check the Engine's Ground Strap and Check the Battery Connections.

Verify that the following conditions exist for the engine's ground strap:
- The connections are secure.
- The connections are not corroded.
- The mating surfaces of the ground are free of paint.

Verify that the battery wiring is properly sized. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections for the battery are clean and secure.

Expected Result:

The engine's ground strap and the battery connections are secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The components are in good condition. Proceed to test step 41.
Not OK - The engine's ground strap and/or the battery connections are not in proper condition.
Repair: Repair the ground strap and/or the battery connections. Replace parts, if necessary.
Proceed to test step 41.

Test Step 41. Check the Earth Ground

Verify that the wiring for the earth ground is properly sized and free of corrosion. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections are free of paint, clean, and secure.

Set the multimeter to the 400 ohm scale. Measure the resistance between the engine block and the earth ground. An independent earth ground is preferred.

Expected Result:

The resistance is less than 2 ohms. The ground is secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The earth ground is in good condition. Proceed to test step 42.
Not OK - The ground is not in proper condition.
Repair: Repair the ground. Replace parts, if necessary.
Proceed to test step 42.

Test Step 42. Check for Detonation

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 43.

Test Step 43. Check the Ground Connection for the Magneto

Show/hide table

There is a strong electrical shock hazard unless the system power is disconnected.

Remove power from the control system. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker in the engine mounted junction box.

Inspect the ground wire to the magneto for loose connections and frayed wire.

Set the multimeter to the 400 ohm scale and measure the resistance between the housing of the magneto and the engine block.

Expected Result:

The resistance is less than 2 ohms. The wire is not frayed and the connections are secure.

Results:

OK - The ground connection for the magneto is good. Proceed to test step 44.
Not OK - The ground connection for the magneto is poor.
Repair: Repair the ground wire or replace the wire, if necessary.
Proceed to test step 44.

Test Step 44. Check the Ground Connections for the Ignition Transformers

Set the multimeter to the 400 ohm scale and measure the resistance between the flange of each ignition transformer and the engine block.

Expected Result:

The resistance for each ignition transformer is less than 2 ohms.

Results:

OK - The ground connections for the ignition transformers are good. Proceed to test step 45.
Not OK - The ground connection for the ignition transformer and the engine block is poor.
Repair: Clean the transformer and/or the valve cover. Replace the components, if necessary.
Proceed to test step 45.

Test Step 45. Check the Secondary Connections for the Ignition Transformers and Check the Extensions.

Remove the ignition transformers and the extensions.

Inspect the secondary connections of the ignition transformers for corrosion and buildup of deposits.

Set the multimeter to the 400 ohm scale and measure the resistance of each extension.

Inspect the connections of the extensions for corrosion and buildup of deposits. Look for pin holes that are caused by arcing.

Expected Result:

The resistance of each extension is less than 2 ohms. The secondary connections of the transformers and the extensions are in good, clean condition.

Results:

OK - The connections and the components are good. Proceed to test step 46.
Not OK - The secondary connections of the transformers and/or the extensions are dirty, corroded, or damaged.
Repair: Clean the components that are affected or replace the components, if necessary.
Proceed to test step 46.

Test Step 46. Check the Spark Plugs

Remove the spark plugs.

Set the multimeter to the 40,000 ohm scale and measure the resistance from the terminal of the spark plug to the center electrode. To ensure an accurate measurement, clean off deposits, if necessary.

Note: For inspection of spark plugs, see the engine's Operation and Maintenance Manual.

Verify that the ground electrode is not shorted to the center electrode. Verify that the spark plug gap is correct. Visually inspect the insulator of the spark plugs for cracks.

Expected Result:

The resistance of each spark plug is less than 20,000 ohms. The spark plug gaps are within specifications. The spark plugs are in good, clean condition.

Results:

OK - Proceed to test step 47.
Not OK - The resistance of the spark plugs is too high. The spark plugs are dirty and/or damaged. The spark plug gap is incorrect.
Repair: Clean the spark plugs or replace the spark plugs, if necessary. Set the spark plug gap to the correct specification.
Proceed to test step 47.

Test Step 47. Check for Detonation

Install the spark plugs, the extensions, and the ignition transformers.

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 48.

Test Step 48. Check the Primary Connections of the Ignition System

Inspect the following connections for damage and/or corrosion: connectors for the ignition transformers, connector for the ignition harness to the magneto and all of the connectors for the ignition harness. Refer to Troubleshooting, "InspectingElectrical Connectors".

Expected Result:

All of the primary connections for the ignition system are in good condition.

Results:

OK - The connections are good. Proceed to test step 49.
Not OK - Parts of the primary connections for the ignition system are damaged and/or corroded.
Repair: Repair the connections or replace parts, if necessary.
Stop.

Test Step 49. Check the Ignition Harness for Short Circuits

Disconnect the ignition harness from the magneto. Disconnect all of the harness connectors from the ignition transformers. Refer to the wiring diagram for the engine.

Set the multimeter to the 400,000 ohm scale. Check for short circuits on the connector for the magneto on the ignition harness. Check each pin of the connector to the following points: +battery, -battery, engine block and all of the other pins on the connector.

Expected Result:

The resistance between the points is greater than 400,000 ohms.

Results:

OK - The ignition harness is free of short circuits. Proceed to test step 50.
Not OK - The ignition harness has at least one short circuit.
Repair: Repair the wiring for the ignition harness and/or the connector. Replace parts, if necessary.
Stop.

Test Step 50. Check the Ignition Harness for Open Circuits

Expected Result:

The resistance to each pin is less than 2 ohms.

Results:

OK - The ignition harness is free of open circuits. Proceed to test step 34.
Not OK - The ignition harness has at least one open circuit.
Repair: Repair the wiring for the ignition harness and/or the connectors. Replace parts, if necessary.
Stop.

Test Step 51. Check the Ground Connection for the Magneto

Show/hide table

There is a strong electrical shock hazard unless the system power is disconnected.

Remove power from the control system. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker in the engine mounted junction box.

Inspect the ground wire to the magneto for loose connections and frayed wire.

Set the multimeter to the 400 ohm scale and measure the resistance between the housing of the magneto and the engine block.

Expected Result:

The resistance is less than 2 ohms. The wire is not frayed and the connections are secure.

Results:

OK - The ground connection for the magneto is good. Proceed to test step 52.
Not OK - The ground connection for the magneto is poor.
Repair: Repair the ground wire or replace the wire, if necessary.
Proceed to test step 52.

Test Step 52. Check the Ground Connections for the Ignition Transformers

Set the multimeter to the 400 ohm scale and measure the resistance between the flange of each ignition transformer and the engine block.

Expected Result:

The resistance for each ignition transformer is less than 2 ohms.

Results:

OK - The ground connections for the ignition transformers are good. Proceed to test step 53.
Not OK - The ground connection for the ignition transformer and the engine block is poor.
Repair: Clean the transformer and/or the valve cover. Replace the components, if necessary.
Proceed to test step 53.

Test Step 53. Check the Secondary Connections for the Ignition Transformers and Check the Extensions

Remove the ignition transformers and the extensions.

Inspect the secondary connections of the ignition transformers for corrosion and buildup of deposits.

Set the multimeter to the 400 ohm scale and measure the resistance of each extension.

Inspect the connections of the extensions for corrosion and buildup of deposits. Look for pin holes that are caused by arcing.

Expected Result:

The resistance of each extension is less than 2 ohms. The secondary connections of the transformers and the extensions are in good, clean condition.

Results:

OK - The connections and the components are good. Proceed to test step 54.
Not OK - The secondary connections of the transformers and/or the extensions are dirty, corroded, or damaged.
Repair: Clean the components that are affected or replace the components, if necessary.
Proceed to test step 54.

Test Step 54. Check the Spark Plugs

Remove the spark plugs.

Set the multimeter to the 40,000 ohm scale and measure the resistance from the terminal of the spark plug to the center electrode. To ensure an accurate measurement, clean off deposits, if necessary.

Note: For inspection of spark plugs, see the engine's Operation and Maintenance Manual.

Verify that the ground electrode is not shorted to the center electrode. Verify that the spark plug gap is correct. Visually inspect the insulator of the spark plug for cracks.

Expected Result:

The resistance of each spark plug is less than 20,000 ohms. The spark plug gaps are within specifications. The spark plugs are in good, clean condition.

Results:

OK - The spark plugs are good. Proceed to test step 55.
Not OK - The resistance of the spark plugs is too high. The spark plugs are dirty and/or damaged. The spark plug gap is incorrect.
Repair: Clean the spark plugs or replace the spark plugs, if necessary. Set the spark plug gap to the correct specification.
Proceed to test step 55.

Test Step 55. Check for Detonation

Install the spark plugs, the extensions, and the ignition transformers.

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 56.

Test Step 56. Check the Primary Connections for the Ignition System.

Inspect the following connections for damage and/or corrosion: connectors for the ignition transformers, connector for the magneto to the ignition harness and all of the connectors for the ignition harness. Refer to Troubleshooting, "Inspecting Electrical Connectors".

Expected Result:

All of the primary connections for the ignition system are in good condition.

Results:

OK - Proceed to test step 57.
Not OK - Parts of the primary connections for the ignition system are damaged and/or corroded.
Repair: Repair the connections or replace parts, if necessary.
Stop.

Test Step 57. Check the Ignition Harness for Short Circuits

Disconnect the ignition harness from the magneto. Disconnect all of the harness connectors from the ignition transformers. Refer to the engine's wiring diagram for the configuration of the wiring.

Set the multimeter to the 400,000 ohm scale. Check each pin of the connector for the magneto on the ignition harness. Check the connector for short circuits to the following points: +battery, -battery, engine block and all of the other pins on the connector.

Expected Result:

The resistance is greater than 400,000 ohms.

Results:

OK - The ignition harness is free of short circuits. Proceed to test step 58.
Not OK - The ignition harness has at least one short circuit.
Repair: Repair the wiring for the ignition harness and/or the connector. Replace parts, if necessary.
Stop.

Test Step 58. Check the Ignition Harness for Open Circuits

Expected Result:

The resistance to each pin is less than 2 ohms.

Results:

OK - The ignition harness is free of open circuits. Proceed to test step 59.
Not OK - The ignition harness has at least one open circuit.
Repair: Repair the wiring for the ignition harness and/or the connectors. Replace parts, if necessary.
Stop.

Test Step 59. Check the Engine's Ground Strap and the Battery Connections

Verify that the following conditions exist for the engine's ground strap:
- The connections are secure.
- The connections are not corroded.
- The mating surfaces of the ground are free of paint.

Verify that the battery wiring is properly sized. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections for the battery are clean and secure.

Expected Result:

The engine's ground strap and the battery connections are secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The components are in good condition. Proceed to test step 60.
Not OK - The engine's ground strap and/or the battery connections are not in proper condition.
Repair: Repair the ground strap and/or the battery connections. Replace parts, if necessary.
Proceed to test step 60.

Test Step 60. Check the Earth Ground

Verify that the wiring for the earth ground is properly sized and free of corrosion. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections are free of paint, clean, and secure.

Set the multimeter to the 400 ohm scale. Measure the resistance between the engine block and the earth ground. Use an independent earth ground.

Expected Result:

The resistance is less than 2 ohms. The ground is secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - Proceed to test step 61.
Not OK - The ground is not in proper condition.
Repair: Repair the ground. Replace parts, if necessary.
Proceed to test step 61.

Test Step 61. Check for Detonation

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 62.

Test Step 62. Verify the Operating Conditions.

Note: This test step is not necessary if the ignition timing, the air/fuel ratio, and the inlet manifold air temperature have already been checked.

Note: The desired timing will vary for different engine applications.

Check the ignition timing.
Use the DDT to check the engine timing. For the correct desired timing for the engine application, see Systems Operation/Testing and Adjusting, SENR4604, "Ignition System".

Note: The air/fuel ratio will vary for different engine applications. The inlet manifold air temperature will affect the air/fuel ratio.

Check the air/fuel ratio.
Verify that the engine is operating with the correct air/fuel ratio. Refer to Systems Operation/Testing and Adjusting, SENR4604, "Fuel System".

Note: The inlet manifold air temperature will affect the air/fuel ratio. The inlet manifold air temperature will vary for different ratings of water temperature regulators (aftercooler).

Check the inlet manifold air temperature.
Verify that the engine is operating with the correct inlet air temperature. Refer to Systems Operation/Testing and Adjusting, SENR4604, "Inlet Manifold Air Temperature".

Expected Result:

The desired timing, the air/fuel ratio, and the inlet manifold air temperature are acceptable.

Results:

OK - The operating conditions are normal. Proceed to test step 63.

Test Step 63. Check the Engine's Ground Strap and Check the Battery Connections.

Verify that the following conditions exist for the engine's ground strap:
- The connections are secure.
- The connections are not corroded.
- The mating surfaces of the ground are free of paint.

Verify that the battery wiring is properly sized. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections for the battery are clean and secure.

Expected Result:

The engine's ground strap and the battery connections are secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The components are in good condition. Proceed to test step 64.
Not OK - The engine's ground strap and/or the battery connections are not in proper condition.
Repair: Repair the ground strap and/or the battery connections. Replace parts, if necessary.
Proceed to test step 64.

Test Step 64. Check the Earth Ground

Verify that the wiring for the earth ground is properly sized and free of corrosion. Ensure that the strands of the wiring are not frayed or broken. Ensure that the connections are free of paint, clean, and secure.

Set the multimeter to the 400 ohm scale. Measure the resistance between the engine block and the earth ground. Use an earth ground that is independent.

Expected Result:

The resistance is less than 2 ohms. The ground is secure, clean, and properly sized. The connections make good contact. The wiring is in good condition.

Results:

OK - The ground is in good condition. Proceed to test step 65.
Not OK - The ground is not in proper condition.
Repair: Repair the ground. Replace parts, if necessary.
Proceed to test step 65.

Test Step 65. Check for Detonation

Operate the engine under the conditions that caused detonation. Check for detonation.

Expected Result:

Detonation no longer occurs.

Results:

OK - The engine is operating normally. Stop.
Not OK - Detonation still occurs. Proceed to test step 66.

Test Step 66. Check the Primary Connections of the Ignition System

Inspect the following connections for damage and/or corrosion: connections for the ignition transformers, connector on the magneto for the ignition harness and all connectors for the ignition harness. Refer to Troubleshooting, "Inspecting Electrical Connectors".

Expected Result:

All of the primary connections for the ignition system are in good condition.

Results:

OK - The connections are good. Proceed to test step 67.
Not OK - Parts of the primary connections for the ignition system are damaged and/or corroded.
Repair: Repair the connections or replace parts, if necessary.
Stop.

Test Step 67. Check the Ignition Harness for Short Circuits

Disconnect the ignition harness from the magneto. Disconnect all of the harness connectors from the ignition transformers. Refer to the engine's wiring diagram for the configuration of the wiring.

Set the multimeter to the 400,000 ohm scale. Check each pin of the connector for the magneto on the ignition harness. Check the connector for short circuits to the following points: +battery, -battery, engine block and all of the other pins on the connector.

Expected Result:

The resistance is greater than 400,000 ohms.

Results:

OK - The ignition harness is free of short circuits. Proceed to test step 68.
Not OK - The ignition harness has at least one short circuit.
Repair: Repair the wiring for the ignition harness and/or the connector. Replace parts, if necessary.
Stop.

Test Step 68. Check the Ignition Harness for Open Circuits.

Expected Result:

The resistance for each pin is less than 2 ohms.

Results:

OK - The ignition harness is free of open circuits. Proceed to test step 69.
Not OK - The ignition harness has at least one open circuit.
Repair: Repair the wiring for the ignition harness and/or the connectors. Replace parts, if necessary.
Stop.

Test Step 69. Check the Ground Connection for the Magneto

Show/hide table

There is a strong electrical shock hazard unless the system power is disconnected.

Remove power from the control system. Turn the engine control switch to the "OFF/RESET" position. Open the circuit breaker in the engine mounted junction box.

Inspect the ground wire to the magneto for loose connections and frayed wire.

Set the multimeter to the 400 ohm scale and measure the resistance between the housing of the magneto and the engine block.

Expected Result:

The resistance is less than 2 ohms.

Results:

OK - The ground connection for the magneto is good. Proceed to test step 70.
Not OK - The ground connection for the magneto is poor.
Repair: Repair the ground wire or replace the wire, if necessary.
Proceed to test step 70.

Test Step 70. Check the Ground Connections for the Ignition Transformers

Set the multimeter to the 400 ohm scale and measure the resistance between the flange of each ignition transformer and the engine block.

Expected Result:

The resistance for each ignition transformer is less than 2 ohms.

Results:

OK - The ground connections for the ignition transformers are good. Proceed to test step 71.
Not OK - The ground connection for the ignition transformer and the engine block is poor.
Repair: Clean the transformer and/or the valve cover. Replace the components, if necessary.
Proceed to test step 71.

Test Step 71. Check the Secondary Connections for the Ignition Transformers and Check the Extensions.

Remove the ignition transformers and the extensions.

Inspect the secondary connections of the ignition transformers for corrosion and buildup of deposits.

Set the multimeter to the 400 ohm scale and measure the resistance of each extension.

Inspect the connections of the extensions for corrosion and buildup of deposits. Look for pin holes that are caused by arcing.

Expected Result:

The resistance of each extension is less than 2 ohms. The secondary connections of the transformers and the extensions are in good, clean condition.

Results:

OK - The connections and the components are good. Proceed to test step 72.
Not OK - The secondary connections of the transformers and/or the extensions are dirty, corroded, or damaged.
Repair: Clean the components that are affected or replace the components, if necessary.
Proceed to test step 72.

Test Step 72. Check the Spark Plugs

Remove the spark plugs.

Set the multimeter to the 40,000 ohm scale and measure the resistance from the terminal of the spark plug to the center electrode. To ensure an accurate measurement, clean off deposits, if necessary.

Note: For inspection of spark plugs, see the engine's Operation and Maintenance Manual.

Verify that the ground electrode is not shorted to the center electrode. Verify that the spark plug gap is correct. Visually inspect the insulator of the spark plug for cracks.

Expected Result:

The resistance of each spark plug is less than 20,000 ohms. The spark plug gaps are within specifications. The spark plugs are in good, clean condition.

Results:

OK - The spark plugs are good. Proceed to test step 73.
Not OK - The resistance of the spark plugs is too high. The spark plugs are dirty and/or damaged. The spark plug gap is incorrect.
Repair: Clean the spark plugs or replace the spark plugs, if necessary. Set the spark plug gap to the correct specification.
Proceed to test step 73.

Test Step 73. Check for Detonation