* Crankshaft Position Sensor (CKP): This sensor is critical. It tells the computer the engine's rotational position, which is essential for proper ignition timing and fuel injection. A faulty CKP sensor will cause random misfires across all cylinders because the computer is receiving inaccurate information. This is a very common cause of this type of problem.
* Camshaft Position Sensor (CMP): Similar to the CKP sensor, a malfunctioning CMP sensor disrupts the timing of the valves and ignition, leading to widespread misfires.
* Ignition Control Module (ICM): The ICM controls the ignition system. If it's failing, it can cause erratic or weak spark delivery to multiple or all cylinders.
* Distributor (if equipped): While less likely given you've changed the coil and wires, a problem within the distributor itself (worn cap, rotor, or internal issues) could affect multiple cylinders. (The 318 in a '96 might or might not have a distributor, depending on the specific engine configuration. This is less likely if you have individual coil packs.)
* Fuel Delivery Problems: A clogged fuel filter, a failing fuel pump, or low fuel pressure can cause a lean condition, leading to misfires across the board. Check fuel pressure.
* Vacuum Leaks: Significant vacuum leaks can disrupt the air/fuel mixture, leading to erratic combustion and misfires.
* PCM (Powertrain Control Module) Issues: While less common, a failing PCM can cause a variety of problems, including random misfires. This is usually a more involved diagnosis.
* Wiring Harness Issues: A damaged or corroded wire in the main harness can cause intermittent or widespread problems.
Troubleshooting Steps:
1. Check Fuel Pressure: This is a quick and easy check that can rule out a fuel delivery problem.
2. Inspect Vacuum Lines: Look for cracks, leaks, or loose connections in all vacuum lines.
3. Check for Diagnostic Trouble Codes (DTCs): Your OBD reader should provide more specific codes beyond the "random misfire" code. These codes can pinpoint the problem area more accurately.
4. Test the CKP and CMP Sensors: These sensors are relatively inexpensive and easy to test with a multimeter or a dedicated scanner. Many auto parts stores will test them for free.
5. Inspect the ICM (if applicable): Visual inspection for obvious damage and testing with a multimeter might be possible.
6. Check the distributor (if applicable): Look for wear and tear on the cap and rotor.
7. Professional Diagnosis: If you're not comfortable with electrical diagnostics, take your truck to a reputable mechanic for a proper diagnosis.
Don't just throw parts at the problem. Systematic troubleshooting based on the OBD codes and these potential causes will save you time and money. The random nature across all cylinders strongly suggests a common component or system failure affecting ignition or fuel delivery.
