If an ignition transformer is suspect, use the following procedure to check the transformer:
- Turn the engine control switch to the OFF/RESET position. Switch the circuit breaker for the engine OFF.
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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. |
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- Remove the valve cover of the suspect cylinder.
- Disconnect the ignition harness from the transformer. Remove the transformer from the engine.
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Pulling on the wiring harness may break the wires. Do not pull on the wiring harness. |
- Inspect the body of the transformer and ground spring (2) for corrosion and/or damage. Verify that screws (1) for the ground spring are secure.
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| Illustration 1 | g01457623 |
(1) Screw for the ground spring (2) Ground spring (3) Adapter (4) Terminal for the spark plug (5) Insulator (6) O-ring seal | |
- Check the insulator near adapter (3) for signs of punch through (pin holes) and/or arcing.
Note: Punch through is caused by misfire in the engine that does not generate a diagnostic code.
- Inspect O-ring seal (6) inside the insulator for damage.
- Remove O-ring seal (6). Inspect terminal (4) inside the insulator for looseness, corrosion, and/or damage. Insert an extra spark plug into the transformer and check for spring pressure of terminal (4) .
- Clean any deposits from the inside of the insulator. Use a 6V-7093 Brush with isopropyl alcohol.
| NOTICE |
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The insulator can be scratched and damaged with a wire brush. Do not use a wire brush on the insulator. |
- Measure the primary circuit by checking the voltage of the diode.
- Set the multimeter to the diode scale. Connect the multimeter leads to the terminals of the 2-pin connector. The polarity of the leads is not important. Measure the voltage between the terminals. Record the measurement.
- Reverse the multimeter leads. Measure the voltage between the terminals again. Record the measurement.
One of the voltage measurements is approximately 0.450 VDC. The other measurement indicates an open circuit.
- Measure the resistance of the secondary circuit.
- Set the multimeter to the 40,000 Ohm scale. Measure the resistance between screw (1) for the ground spring and terminal (4) for the spark plug.
Note: The resistance of the secondary coil will vary with the temperature. Illustration 2 demonstrates the relationship between the secondary coil's resistance and the temperature. A reading that is within ± 1000 ohms is acceptable.
- Set the multimeter to the 40,000 Ohm scale. Measure the resistance between screw (1) for the ground spring and terminal (4) for the spark plug.
- Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.
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| Illustration 2 | g01170387 |
- 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 a diagnostic code.
If the problem follows the transformer, replace the transformer. Make sure that you use the correct transformer for the engine. Reset the control system. Clear any logged diagnostic codes.
If the problem stays with the cylinder, there is a problem with the spark plug or the electrical circuit for the transformer.
For troubleshooting of the electrical circuit, refer to the Troubleshooting Manual.
Spark Plug
If a diagnostic code is generated for the ignition transformer's secondary circuit, the spark plug may need to be replaced. Misfire and a cold cylinder are other indications of a worn spark plug. Use Cat ET to monitor the exhaust port temperatures in order to locate a cold cylinder.
The service life of the spark plugs is affected by fouling due to deposits from the oil and by peak voltage. Maintenance of the ignition system is also affected by voltage. Higher voltage is required by higher inlet manifold air pressure, a higher compression ratio, or retardation of the timing. Higher voltage reduces the service life of components such as spark plugs, wires, and transformers.
To help predict the spark plug's service life, use Cat ET to monitor the parameter. The value of this parameter will increase as the spark plug gap wears over time. Maintaining a log of this parameter at a particular site will help to determine the proper interval for replacement of the spark plugs.
For instructions on inspection and replacement of the spark plug, refer to the engine's Operation and Maintenance Manual. For more information on the spark plug, refer to the engine's Specifications manual.