Ignition System: Description and Operation

3.7L







The ignition system is controlled by the Powertrain Control Module (PCM) on all engines.

This engine shares an ignition coil (2) and an ignition cable (1) between the two cylinders. The three coils fit into machined holes in the cylinder head for cylinders 1, 3, and 5. Rubber boots seal the secondary terminal ends of the coils to the top of the spark plugs. The spring is used for a mechanical contact between the coil and the top of the spark plug. These rubber boots and springs are a permanent part of the coil and are not serviced separately. An O-ring is used to seal the coil at the opening into the cylinder head. A separate electrical connector is used for each coil.

The 3.7L engine uses a distributorless waste spark system. In a wasted spark system, the spark plugs fire in pairs even though one is on its compression stroke and one is on its exhaust stroke. The extra spark on the exhaust stroke has no effect and is thus "wasted". This design halves the number of components in a typical ignition system

Two knock sensors (one for each cylinder bank) are used to help control spark knock.

The Auto Shutdown (ASD) relay provides battery voltage to each ignition coil.

The ignition system consists of:

- 6 Spark Plugs
- 3 Separate Ignition Coils
- 3 Separate Ignition Cables
- 2 Knock Sensors
- Powertrain Control Module (PCM)
- Also to be considered part of the ignition system are certain inputs from the Crankshaft Position, Camshaft Position, 2 knock and MAP Sensors