VALVE 8F8858 - Caterpillar

The engine is equipped with an electronic ignition system. The system provides dependable firing and low maintenance. The system provides precise control of the spark and of the ignition timing for each cylinder. Illustration 1 is a diagram of the main components in the ignition system.
Illustration 1 g00990326
Diagram of the ignition system
Illustration 2 g00909021
(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 in order to create a spark across the spark plug electrode.Initially, the operator determines the ignition timing by using the Caterpillar Electronic Technician (ET) to program the "First Desired Timing" and "Second Desired Timing" parameters. A switch is used to select the appropriate timing. The ECM makes slight adjustments to the actual timing during operation.During operation, the ECM monitors a signal from the engine speed/timing sensor. The sensor monitors the rotation of the timing wheel which has a special tooth pattern. Through monitoring of the sensor's signal, the ECM is able to calculate the crankshaft position. This enables the ECM to properly initiate the timing of each spark.Detonation sensors monitor the engine for detonation. The engine has eight detonation sensors. Each sensor monitors two adjacent cylinders. The sensors generate data on vibration that is processed by the ECM in order to determine detonation levels.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 five seconds and the cylinder is still detonating, the ECM shuts down the engine.The ECM provides extensive diagnostics for 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.
Illustration 3 g00986986
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 32,000 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.