Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Engine Ignition
The electronic ignition (El) system for the 3.9L and the 4.2L engines consists of the following components:
- crankshaft position (CKP) sensor
- ignition coil
- spark plugs
- spark plug wires
The crankshaft position (CKP) sensor:
- is a variable reluctance sensor.
- is mounted on the engine front cover.
- is triggered by a 36-minus-l tooth trigger wheel located on the crankshaft pulley and damper.
- provides base timing and crankshaft speed (RPM) to the powertrain control module (PCM).
For additional information, refer to ELECTRONIC ENGINE CONTROLS . The ignition coil:
- is controlled by the powertrain control module.
- fires 2 spark plugs simultaneously.
The spark plugs:
- ignite the fuel and air mixture.
- are platinum enhanced for long life.
The spark plug wires:
- carry high voltage pulses from the ignition coil to the spark plugs.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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