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| Illustration 1 | g00909021 |
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(1) Valve cover
(2) Transformer (3) Camshaft cover (4) Ignition harness | |
Each cylinder has an ignition transformer that is located under the valve cover. To initiate combustion, the Electronic Control Module (ECM) sends a pulse of approximately 100 volts to the primary coil of each ignition transformer at the appropriate time and for the appropriate duration. The transformers increase the voltage to create a spark across the spark plug electrode.
The operator determines the base ignition timing by using the Caterpillar Electronic Technician (ET) to program the "First Desired Timing" parameter. The ECM makes adjustments to the actual timing during operation.
There are three engine speed timing sensors for the engine:
- One is on the crankshaft flywheel housing.
- One is on the front housing at the left camshaft.
- One is on the front housing at the right camshaft.
The crankshaft sensor detects a hole in the face of the flywheel, to determine crankshaft position.
Timing wheels are mounted to the front of both camshafts.
The timing wheels have a special tooth pattern and are monitored by the cam sensors.
The engine performs a timing calibration automatically, during every startup, based on the speed/timing signals from the crankshaft and the camshafts.
The ECM utilizes all three sensors to determine the crankshaft position and engine speed to calculate the next desired ignition signal.
If any one of the three sensor signals are lost the ignition will be disabled.
Detonation sensors monitor the engine for detonation. Each sensor monitors two adjacent cylinders. The sensors generate data on vibration that is processed by the ISM to determine detonation levels. The ISM monitors detonation from 0-30 deg ATDC for each cylinder.
If detonation occurs, the ECM retards the ignition timing of the affected cylinder or cylinders up to six degrees. If a cylinder has been fully retarded for 16 combustion cycles and the cylinder is still detonating, the ECM shuts down the engine. During a detonation shutdown request, the ECM retards the detonating cylinder an additional six degrees, not to exceed ten degrees total.
The ECM provides diagnostics for the ignition system. Refer to the engine Troubleshooting manual for more information on the diagnostics of the ignition system.
Ignition Transformers and Spark Plugs
Note: Ignition transformers from Electronic Ignition Systems (EIS) are not interchangeable with the transformers in this engine.
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| Illustration 2 | g06267929 |
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Ignition transformer and spark plug (1) Ground spring (2) Primary connection (3) Secondary connection (4) Extension (5) O-ring seal (6) Spark plug | |
Each transformer is grounded to a valve cover via ground spring (1). The ignition harness is connected to primary connection (2) which receives the pulse of approximately 100 volts. The output from the secondary circuit of the transformer is sent to the spark plug through secondary connection (3). The transformer's secondary circuit provides an initial 8,000 to 39,000 V to the spark plug in order to create a spark which ignites the air/fuel mixture in the cylinder.
Generator set applications use a spark plug with a precombustion chamber.
Industrial applications use the standard style of spark plug.