* Coil itself: The most obvious possibility is a faulty coil. These can fail internally, causing a lack of spark. A visual inspection for cracks or obvious damage is a good starting point, but testing with a multimeter (to check resistance) is necessary for confirmation.
* Ignition Control Module (ICM): The ICM controls the firing order of the coils. A faulty ICM can prevent a specific coil from firing, or cause erratic firing across all coils. This is a common point of failure in these cars. Testing is crucial, usually involving a back-probing method to check for pulses.
* Wiring: A break or short in the wiring leading to the middle coil will prevent it from receiving power or the necessary trigger signal. Visually inspect the wiring harness for damage, corrosion, or loose connections. A continuity test with a multimeter is needed to fully rule out wiring problems.
* Crankshaft Position Sensor (CKP): The CKP tells the ICM when to fire the coils. A faulty CKP will result in inconsistent or no firing across all cylinders, including the middle coil's cylinders.
* Cam Position Sensor (CMP): Similar to the CKP, a failing CMP can disrupt the ignition timing, possibly leading to a lack of spark in one or more cylinders.
* Power Supply: Make sure the coil is receiving the correct voltage. A low voltage supply to the coil could prevent it from firing. Check fuses and relays related to the ignition system.
* Grounds: Poor grounding can interrupt the electrical flow, causing intermittent or complete failure of the ignition system. Clean and check all grounds related to the ignition system.
Troubleshooting Steps:
1. Visual Inspection: Check for any obvious damage to the coil, wiring, and connectors.
2. Testing: Use a multimeter to test the coil's resistance (compare to specifications found in a repair manual), check the wiring for continuity, and test the ICM (this requires a more specialized approach and often a factory service manual).
3. Check for Codes: If the car has diagnostic capabilities (check engine light), read the trouble codes using an OBD-I scanner (or consult a mechanic). These codes can pinpoint the problem more accurately.
4. Process of Elimination: Start with the simplest and most likely culprits (coil and wiring), then move to the more complex components (ICM, sensors).
Without proper diagnostic tools and knowledge of automotive electrical systems, attempting repairs can be risky. If you're not comfortable performing these tests, it's best to consult a qualified mechanic specializing in older vehicles. They'll have the necessary tools and expertise to diagnose and repair the problem efficiently.
