* Worn or Damaged Distributor Cap/Rotor: Even new parts can be defective. Inspect the cap and rotor *very carefully* for cracks, carbon tracking (blackened areas), or any other damage. A microscopic crack can significantly reduce spark strength.
* Wires Misrouted or Damaged: Double-check that all spark plug wires are properly seated on both the distributor cap and spark plugs. Make sure they're not pinched, frayed, or touching each other. Even a slight gap in the insulation can cause a short or weak spark.
* Worn or Damaged Pickup Coil: While you replaced the pickup coil, it's possible the replacement is faulty or the old one damaged something else (like the distributor shaft) during its removal/installation. This component is crucial for triggering the ignition coil.
* Ignition Control Module (ICM): The ICM is a common point of failure in these trucks. It's responsible for controlling the timing and duration of the spark. A failing ICM can result in a weak or intermittent spark.
* Coil Issues (despite strong initial spark): While you see a strong spark at the coil, it might be weakening significantly by the time it reaches the plugs. The coil itself might be nearing the end of its life, or there's a problem with its internal resistance.
* Distributor Shaft/Gear Wear: Excessive wear on the distributor shaft or gear can lead to poor timing or prevent proper signal transfer to the coil, weakening the spark.
* High Resistance in Wiring: Even with new wires, there might be a high resistance somewhere in the circuit. Check the resistance of each wire individually using an ohmmeter.
Troubleshooting Steps:
1. Visually Re-Inspect EVERYTHING: Carefully examine the distributor cap, rotor, and spark plug wires *again*. Look for any imperfections, however small.
2. Check Spark Plug Gap: Ensure the spark plug gap is correct according to the manufacturer's specifications. An incorrect gap can severely weaken the spark.
3. Test the ICM: This often requires a multimeter and some knowledge of automotive electrical systems. A failing ICM often exhibits inconsistent or weak spark output. A mechanic's test light or a dedicated automotive diagnostic tool can also help.
4. Use a Spark Tester: A spark tester (inline or clamp-on) connected directly to the spark plug wires will give a clearer indication of the spark strength at each cylinder, revealing if the problem is consistent across all cylinders or isolated to one or more.
5. Check for Ignition System Codes: If your truck has a diagnostic port (OBD I or OBD II, depending on the year and exact model), you might be able to retrieve diagnostic trouble codes (DTCs) that will pinpoint the issue more precisely. An OBD reader is needed.
If you're not comfortable working on the ignition system yourself, it's best to take your truck to a qualified mechanic. Working on the ignition system can be dangerous if not handled correctly.
