G3520B Industrial Engine Caterpillar

The ignition transformers initiate combustion by providing high voltage to the spark plugs. The positive output from the secondary circuit of the transformer is at the connection for the terminal of the transformer and the terminal of the spark plug. The transformers are located underneath the valve covers. Each transformer is grounded to a valve cover via a ground spring.

The secondary circuit of the transformer provides an initial 8,000 to 37,000 volts to the spark plug. This voltage ionizes the spark plug gap. This voltage is then reduced to about 1000 volts. The total duration of the spark is approximately 400 microseconds.

Each Electronic Control Module (ECM) can diagnose the primary circuit of the ignition transformers for open circuits and/or for short circuits. Secondary open circuits and short circuits will not directly shut down the engine. However, these conditions may lead to misfire which can cause lugging of the engine. Lugging of the engine can cause a shutdown.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

Note: Ignition transformers from Electronic Ignition Systems (EIS) are not interchangeable with the transformers in this engine.

Caterpillar spark plugs are high voltage devices with internal resistors. The spark plugs operate at a voltage that is greater than 5,000 volts.

Most ignition systems are not affected by resistance in the secondary circuit. If a measurement of the resistance is desired, a megohmmeter must be used. A low voltage multimeter will not provide a reliable reading of the resistance because oxidation of the spark plug's internal components will affect the readings of those meters.

Test Step 1. Check the Status Screen of Cat ET for the Output of the Secondary Circuits of the Transformers

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Connect Cat ET to the service tool connector.

3. Restore the electrical power to the engine. Set the engine control to the STOP mode.

4. Set up two status screens for Cat ET. Use eight of the following labels for parameters on each Status screen:
   Show/hide table

   Table 1

   Parameters for the Status Screens on Cat ET
   Screen 1 Group 8	Screen 2 Group 9
   "Cylinder #1 Transformer Secondary Output Voltage Percentage"	"Cylinder #2 Transformer Secondary Output Voltage Percentage"
   "Cylinder #3 Transformer Secondary Output Voltage Percentage"	"Cylinder #4 Transformer Secondary Output Voltage Percentage"
   "Cylinder #5 Transformer Secondary Output Voltage Percentage"	"Cylinder #6 Transformer Secondary Output Voltage Percentage"
   "Cylinder #7 Transformer Secondary Output Voltage Percentage"	"Cylinder #8 Transformer Secondary Output Voltage Percentage"
   "Cylinder #9 Transformer Secondary Output Voltage Percentage"	"Cylinder #10 Transformer Secondary Output Voltage Percentage"
   "Cylinder #11 Transformer Secondary Output Voltage Percentage"	"Cylinder #12 Transformer Secondary Output Voltage Percentage"
   "Cylinder #13 Transformer Secondary Output Voltage Percentage"	"Cylinder #14 Transformer Secondary Output Voltage Percentage"
   "Cylinder #15 Transformer Secondary Output Voltage Percentage"	"Cylinder #16 Transformer Secondary Output Voltage Percentage"
   "Cylinder #17 Transformer Secondary Output Voltage Percentage"	"Cylinder #18 Transformer Secondary Output Voltage Percentage"
   "Cylinder #19 Transformer Secondary Output Voltage Percentage"	"Cylinder #20 Transformer Secondary Output Voltage Percentage"

5. Start the engine. Apply the normal load at rated speed. Allow the engine to warm up to normal operating temperature.

6. Observe the value of the output for the secondary circuit of each transformer.

Expected Result:

The displayed value of the output for the secondary circuit of each transformer is between 1 and 90 percent.

Results:

• OK - The displayed value of the output for the secondary circuit of each transformer is between 1 and 90 percent. The ignition system components are operating properly.

  Repair: Investigate other possible root causes of the problem. Troubleshoot the symptom. Refer to Troubleshooting, "Troubleshooting Without A Diagnostic Code".

  Stop.

• Not OK - At least one of the outputs displayed a value of 0 percent or a value that is greater than 90 percent. The ignition system components require maintenance. Proceed to Test Step 2.

Test Step 2. Inspect the Transformer

Show/hide table

Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

Show/hide table



Illustration 1	g01091169
Section view of the side of a cylinder head (1) Valve cover (2) 2-pin connector (3) Transformer

2. Remove valve cover (1) of the suspect cylinder.

Show/hide table

NOTICE
Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.

3. Disconnect 2-pin connector (2). Remove transformer (3) from the engine.

Show/hide table



Illustration 2	g01091835
Ignition transformer and extension (3) Transformer (4) Screws for the ground spring (5) Ground spring (6) Spacer (7) Secondary terminal for the spark plug (8) Extension (9) O-ring seal

4. Inspect the body of transformer (3) and ground spring (5). Verify that there is no corrosion nor damage. Verify that the screws for ground spring (4) are secure.

5. Inspect secondary terminal (7) for corrosion and/or for damage.

6. Inspect O-ring seal (9) inside extension (8) for damage.

7. Check for a secure connection between the transformer and the spark plug.

Note: Punch through is caused by misfire in the engine that does not generate a diagnostic code.

8. Check extension (8) near spacer (6) for signs of punch through (pin holes) and/or of arcing.

Show/hide table

NOTICE
The extension can be scratched and damaged with a wire brush. Do not use a wire brush on the extension.

9. Clean any deposits from the inside of the extension. Use a 6V-7093 Brush with isopropyl alcohol.

Expected Result:

The transformer is in good condition.

Results:

• OK - The transformer is in good condition. Proceed to Test Step 3.

• Not OK - An inspection found a problem with the transformer.

  Repair: Repair the transformer, when possible. Replace the transformer, if necessary. Be sure to use the correct transformer for the G3500B Engine.Reset the control system. Restart the engine. Clear the logged codes.

  Stop.

Test Step 3. Check the Primary Circuit and the Secondary Circuit

Show/hide table



Illustration 3	g01091176
Schematic for the primary circuit and for the secondary circuit (10) 2-pin connector for the transformer (11) + Terminal (12) - Terminal (13) Flyback diode (14) Blocking diode (15) Primary coil of the transformer (16) Secondary coil of the transformer (17) Resistor (18) Spark plug gap

1. Measure the primary circuit by checking the voltage of blocking diode (14) .
   Show/hide table
   
   

   Illustration 4	g01091178
   Ignition transformer and extension (11) + Terminal (12) - Terminal (4) Screw for the ground spring (7) Secondary terminal for the spark plug

   1. Set the multimeter to the diode scale. Connect the multimeter leads to terminals (11) and (12) of the 2-pin connector. The polarity of the leads is not important. Measure the voltage between the terminals. Record the measurement.

   2. Reverse the multimeter leads. Measure the voltage between the terminals again. Record the measurement.

2. Measure the resistance of the secondary circuit.

   Note: The resistance of the secondary coil will vary with the temperature. Illustration 5 demonstrates the relationship between the secondary coil's resistance and the temperature. A reading that is within 1000 Ohms is acceptable. For example, if the transformer's temperature is 60 °C (140 °F), the correct resistance is between 21,000 and 23,000 Ohms.

   Show/hide table
   
   

   Illustration 5	g00863850
   Resistance versus temperature (Y) Resistance in Ohms (X) Temperature in degrees celsius (degrees fahrenheit)

   1. Set the multimeter to the 40,000 Ohm scale. Measure the resistance between the screw for the ground spring (4) and the secondary terminal for the spark plug (7) .

Expected Result:

For the primary circuit, one of the voltage measurements is approximately 0.450 VDC. The other voltage measurement indicates an open circuit.

For the secondary circuit, the resistance between the screw for the ground spring and the secondary terminal for the spark plug is within the acceptable tolerance.

Results:

• OK - All three of the measurements are correct. Proceed to Test Step 4.

• Not OK - At least one of the measurements is incorrect.

  Repair: Make sure that the engine control switch to the OFF/RESET position and the electrical power is removed from the engine. Replace the ignition transformer. Make sure that you use the correct transformer for the G3500B Engine.

  Stop.

Test Step 4. Check the Spark Plug

1. Remove the electrical power from the engine.

2. Perform the following procedures according to the instructions in the engine's Operation and Maintenance Manual.

   1. Remove the spark plug from the cylinder head.

   2. Inspect the spark plug.

   3. Clean the spark plug.

3. Measure the spark plug's resistance after the spark plug has been cleaned.

   Note: A standard Ohmmeter cannot be used for measuring the resistance of a used spark plug.

   1. Use the 142-5055 Insulation Testing Gp (Electrical) to measure the resistance of the spark plug. Follow the warnings and instructions that are provided with the tool.

   2. Connect the red lead of the tester to the terminal post. Because the ground strap is close to the center electrode, you will need to connect a smaller lead to the center electrode. Then connect the black lead of the tester to the smaller lead.

   3. Use the tester's "20 KOhms" scale.

Expected Result:

The spark plug is in good condition.

The resistance is less than 10,000 Ohms.

Results:

• OK - The spark plug is in good condition. The resistance is less than 10,000 Ohms. Proceed to Test Step 5.

• Not OK - The spark plug is not in good condition and/or the resistance is not within the specification.

  Repair: Discard the spark plug. Install a new spark plug according to Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace - Spark Plugs with Adjustable Electrode Gaps".Reset the control system. Restart the engine. Clear the logged codes.

  Stop.

Test Step 5. Operate the Engine

1. Install the spark plug according to the instructions in the engine's Operation and Maintenance Manual.

2. Install the transformer and the valve cover.

3. Reset the control system. Clear any logged diagnostic codes.

4. Start the engine and operate the engine in order to generate the diagnostic code again.

Expected Result:

A diagnostic code is not generated.

Results:

• OK - A diagnostic code is not generated. Proceed with normal operation. Stop.

• Not OK - A diagnostic code is generated. Proceed to Test Step 6.

Test Step 6. Isolate the Spark Plug and the Transformer

1. Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.

2. Reset the control system. Clear any logged diagnostic codes.

3. Start the engine and operate the engine in order to generate the diagnostic code again.

Expected Result:

The diagnostic code is generated for the suspect transformer.

Results:

• Yes - The diagnostic code is generated for the suspect transformer.

  Repair: Make sure that the engine control is in the OFF/RESET mode and that the electrical power is removed from the engine. Replace the faulty transformer. Make sure that you use the correct transformer for the G3500B Engine. Reset the control system. Clear any logged diagnostic codes.

  Stop.

• No - The diagnostic code is generated for the original cylinder.

  Repair: Make sure that the engine control is in the OFF/RESET mode and that the electrical power is removed from the engine. Install a new spark plug according to the instructions in Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace - Spark Plugs with Adjustable Electrode Gaps". Reset the control system. Clear any logged diagnostic codes.

  Stop.