Grand Cherokee 2006-2007

Diagnosis & Testing


The 3.7L V6, 4.7L and 5.7L V8 engines use an advanced distributorless ignition system. A dedicated ignition coil is mounted above each spark plug and bolted to the engine. Dedicated ignition coils as well as spark plug cables are employed on 2005 5.7L engines, which utilize 2 spark plugs per cylinder.

The main components of the ignition system are:

Powertrain control module (PCM)
Ignition coils
Spark plug cables
Spark plugs
Crankshaft and camshaft position sensors.

The PCM automatically regulates the spark advance to fire the spark plugs according to input from various engine sensors. The input signals are then used to compute the optimum ignition timing for the lowest exhaust emissions and best driveability. During the crank-start period, ignition timing advance is set to ensure quick and efficient starting.

The amount of electronic spark advance provided is determined by four input factors: coolant temperature, engine rpm, throttle position and available manifold vacuum. On some late model systems, intake manifold temperature is also used. Gear selection may also be a factor.

Battery voltage is supplied to each coil by the Automatic Shutdown (ASD) relay. The PCM opens and closes each coil's ground circuit at a specific time to fire the plug.

By controlling the coil ground circuit, the PCM is able to set the base timing and adjust the ignition timing advance. This is done to meet changing engine conditions.

Base ignition timing is set by the PCM and is not adjustable.

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Fig. Ignition coil components. Primary winding resistance is measured at the electrical connector terminals

Component tests are limited to checks of the spark plugs and coils. Specialized analysis equipment is needed for more in-depth troubleshooting.

Do not run the engine with a coil disconnected. Do not attempt to ground a coil to the engine to check for spark. Sensitive components could be ruined or the extremely high voltage could cause serious injury or death.