Possible Culprits:
* Wiring Harness Issues (Beyond the Injector Harness): While you checked the injector harness on the right side, problems can exist *elsewhere* in the main harness. Look for:
* Chafing or broken wires: Carefully inspect the entire wiring harness, paying close attention to areas that bend or flex frequently (engine bay, firewall). Look for cracks in the insulation, exposed wires, or broken strands.
* Corrosion: Check connectors for corrosion. Clean them with contact cleaner and a wire brush if necessary.
* Poor connections: Make sure all connectors are securely seated.
* Fuel Pump/Pressure Regulator: The "sporadic fuel" suggests a problem here.
* Fuel Pressure Test: This is crucial. You need a fuel pressure gauge to measure the fuel pressure at the fuel rail. The specifications should be in your repair manual or online. Low pressure, inconsistent pressure, or pressure that drops off quickly points to a failing fuel pump or regulator.
* Fuel Pump Relay: A failing relay could intermittently power the pump.
* Fuel Filter: A clogged fuel filter can restrict fuel flow.
* Ignition System (Beyond the Module): Even though you replaced the ignition module, other components could be at fault:
* Distributor Cap and Rotor: Cracks or worn contacts can cause misfires and poor starting. Inspect closely.
* Ignition Coil: A weak or failing coil can lead to intermittent misfires.
* Pick-up Coil (in distributor): This provides the signal for the ignition module, a faulty one can cause intermittent operation.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A faulty CKP can cause hard starting, misfires, and poor running.
* Mass Airflow Sensor (MAF): A bad MAF sensor will cause erratic fuel delivery.
* Throttle Position Sensor (TPS): A faulty TPS can result in improper fuel delivery and idle issues.
* Vacuum Leaks: Small vacuum leaks can significantly impact engine performance. Check all vacuum lines for cracks, leaks, and proper connections. Pay attention to the intake manifold gasket and PCV system.
Troubleshooting Steps:
1. Fuel Pressure Test: This is the most important next step.
2. Thorough Wiring Inspection: Don't just focus on the injector harness. Examine the entire harness.
3. Visual Inspection of Ignition Components: Check the distributor cap, rotor, and coil for signs of wear or damage.
4. Vacuum Leak Test: Use a vacuum gauge or smoke test to detect leaks.
5. Check for Diagnostic Trouble Codes (DTCs): Your truck likely has a diagnostic port. A code reader can provide valuable information about what the computer has detected.
Important Note: Working on fuel systems involves flammable liquids. Always take appropriate safety precautions. If you're not comfortable performing these checks, take your truck to a qualified mechanic. The intermittent nature of the problem makes diagnosis difficult without the proper tools and experience.
