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.
| |
| Illustration 1 | g01075050 |
|
Ignition transformer and spark plug (1) Ground spring (2) 2-pin connector (3) secondary spark plug terminal (4) Extension (5) O-ring seal (6) Hole in the spark plug's precombustion chamber | |
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.
The 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 an 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
- Set the engine control to the OFF/RESET mode. Switch 16 amp circuit breaker (1) to the OFF position.
- Connect Cat ET to the service tool connector on the terminal box.
- Set the engine control to the STOP mode. Switch the 16 amp circuit breaker ON.
- 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 8Screen 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" - Start the engine. Apply the normal load at rated speed. Allow the engine to warm up to normal operating temperature.
- Observe the value of the output for the secondary circuit of each transformer.
| |
| Illustration 2 | g01077040 |
|
Terminal box (1) 16 amp circuit breaker | |
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
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
Show/hide table
Illustration 3 g01075051 Section view of a valve cover and ignition transformer
(1) Valve cover
(2) 2-pin connector - Remove valve cover (1) for the suspect cylinder.
Show/hide table
NOTICE Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.
- Disconnect the ignition harness from the ignition transformer. Remove the transformer from the engine.
Show/hide table
Illustration 4 g01075053 Ignition transformer and extension
(1) Screw
(2) Ground spring
(3) Spacer
(4) Secondary terminal for the spark plug
(5) Extension
(6) O-ring seal - Inspect the body of the transformer and the ground spring for corrosion and/or for damage. Verify that the screws (1) for ground spring (2) are secure.
- Inspect secondary terminal (4) for the spark plug inside the extension for corrosion and/or damage.
- Inspect O-ring seal (6) inside the extension for damage.
- 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.
- Check the extension near the spacer for signs of punch through (pin holes) and/or 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.
- Clean any deposits from the inside of the extension. Use a 6V-7093 Brush with isopropyl alcohol.
 |
|
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. |
Expected Result:
The transformer is in good condition.
Results:
- OK - The transformer appears to be 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
- Check the primary circuit and check the secondary circuit according to Systems Operation, Testing and Adjusting, RENR2268, "Ignition Transformer".
Expected Result:
The ignition transformer is within the specifications that are outlined in Systems Operation, Testing and Adjusting, RENR2268, "Ignition Transformer".
Results:
- OK - All 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 is in the OFF/RESET mode and that the 16 amp circuit breaker is OFF. Replace the ignition transformer. Make sure that you use the correct transformer for the G3500B Engine.
STOP
Test Step 4. Check the Spark Plug
- Switch the 16 amp circuit breaker OFF.
Show/hide table
Illustration 5 g00837850 Spark plug that has a precombustion chamber - Perform the following procedures according to the instructions in the engine's Operation and Maintenance Manual.
- Remove the spark plug from the cylinder head.
- Inspect the spark plug.
- Clean the spark plug.
Note: For a spark plug with a precombustion chamber, the resistance cannot be measured. The minimum service life of a spark plug with a precombustion chamber is approximately 3000 service hours. The spark plug may be good for a considerable period beyond 3000 service hours. Experience at the particular site will help to determine the proper interval for replacement of the spark plug.
Expected Result:
The spark plug is in good condition.
Results:
- OK - The spark plug is in good condition. Proceed to Test Step 5.
- Not OK - The spark plug is not in good condition.
Repair: Discard the spark plug. Install a new spark plug according to the instructions in the engine's Operation and Maintenance Manual.
Reset the control system. Restart the engine. Clear the logged codes.
STOP
Test Step 5. Operate the Engine
- Install the spark plug according to the instructions in the engine's Operation and Maintenance Manual.
- Install the transformer and the valve cover.
- Reset the control system. Clear any logged diagnostic codes.
- 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
- Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.
- Reset the control system. Clear any logged diagnostic codes.
- 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 16 amp circuit breaker is OFF. 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 16 amp circuit breaker is OFF. Install a new spark plug according to the instructions in Operation and Maintenance Manual, "Ignition System Spark Plugs - Check/Adjust/Replace". Reset the control system. Clear any logged diagnostic codes.
STOP