1. Ignition System:
* Ignition Coil: A faulty ignition coil won't provide the necessary high voltage to the spark plugs, even with new plugs. Test the coil's output with a spark tester or a multimeter (check your vehicle's repair manual for specifics). A weak or no spark indicates a problem with the coil.
* Ignition Module (Distributor): On a 4.9L, the ignition module is often integrated into the distributor. A failing module can prevent a consistent or strong spark. Testing this requires specialized tools or an understanding of distributor testing procedures. A visual inspection for cracks or obvious damage is a good starting point.
* Distributor Cap and Rotor: Check these for cracks, carbon tracking, or wear. A worn or damaged cap and rotor can prevent proper spark distribution to the cylinders. Replace if necessary.
* Ignition Switch: A faulty ignition switch won't send power to the necessary components. Try wiggling the key while in the "start" position to see if that affects anything. This is less likely, but possible.
* Wiring: Inspect all wiring related to the ignition system for corrosion, breaks, or loose connections. Pay close attention to the wiring leading to the coil, distributor, and spark plugs.
2. Engine Control System (ECM/PCM):
* Crankshaft Position Sensor (CKP): This sensor tells the ECM where the crankshaft is in its rotation. A faulty CKP sensor prevents the ECM from sending the signal to fire the spark plugs at the right time.
* Cam Position Sensor (CMP): (Less common on the 4.9L but worth a check) Similar to the CKP, the CMP sensor tells the ECM the camshaft's position. A faulty CMP will also prevent proper timing.
* ECM/PCM itself: Although less likely, a faulty ECM/PCM can cause numerous starting problems. This requires advanced diagnostic tools to test.
3. Other Considerations:
* Fuel Pressure: While you say the fuel pump is working, verify *actual* fuel pressure using a fuel pressure gauge. The pump might be working, but the pressure might be too low.
* Air Intake: Make sure there are no obstructions in the air intake system. A clogged air filter or other restrictions can prevent the engine from starting.
* Battery and Cables: A weak battery or corroded battery cables can prevent enough current from reaching the starter motor. Test the battery voltage.
* Starter Motor: While less likely given the spark plug issue, a failing starter could prevent cranking.
Troubleshooting Steps:
1. Visual Inspection: Thoroughly inspect all components mentioned above for obvious damage or corrosion.
2. Spark Test: A basic spark test on a spark plug wire connected to a grounded plug will help determine if you are getting spark.
3. Fuel Pressure Test: Check fuel pressure to eliminate any fuel delivery issues.
4. Consult a Repair Manual: A repair manual specific to your 1994 Ford F-150 4.9L will provide detailed diagrams, testing procedures, and specifications for all the components mentioned above. This is crucial for accurate testing and diagnosis.
If you are not comfortable performing these checks yourself, take the vehicle to a qualified mechanic. They have the tools and expertise to properly diagnose the problem. Remember safety first when working on your vehicle.
