1. Check the Basics:
* Fuel Pump: Is the fuel pump functioning? Listen for the pump's whine when the ignition is turned on (but the engine isn't cranking). If you don't hear it, check the fuel pump relay and fuse. Low fuel pressure can also manifest as intermittent injector pulse.
* Fuel Pressure: Even if the pump runs, it might not be producing enough pressure. A fuel pressure gauge is necessary to accurately measure this. Low pressure can be due to a weak pump, clogged filter, or problems in the fuel delivery system.
* Battery Voltage: A weak battery or poor connections can affect the engine's ability to provide sufficient power for the ignition system and injectors. Check the battery voltage with a multimeter.
* Ignition System: Problems with the ignition system (distributor cap, rotor, ignition coil, ignition module) can interrupt the signal to the injectors. Inspect these components for cracks, corrosion, or damage.
* Engine Cranking Speed: If the engine cranks slowly, it might not generate enough power to trigger the injectors reliably. Check the battery and starter motor.
2. Focus on the Injector Pulse Signal:
* PCM (Powertrain Control Module): The PCM controls the injector pulse. A faulty PCM is a possibility, but less likely than the issues above. Diagnosing a PCM problem typically requires specialized tools and expertise.
* Wiring and Connectors: Inspect the wiring harness from the PCM to the injectors for broken wires, corrosion, loose connectors, or chafing. Pay close attention to the connectors at both ends.
* Injector Wiring Harness: Check the wiring harness at the injector itself for any signs of damage or poor connection. Sometimes the wire insulation can degrade or the connector pins can become corroded, leading to intermittent signal loss.
* Injector Driver Circuit: Inside the PCM, the injector driver circuit sends signals to the injectors. Issues in this circuit are less common but possible. This is a more advanced diagnostic procedure.
* Cranking Sensor (CKP): The crankshaft position sensor tells the PCM the engine's rotational position. A faulty CKP can prevent the PCM from delivering the injector pulse signal accurately, especially during cranking.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP can cause erratic or absent injector pulse.
3. Diagnostic Tools:
* Multimeter: Use a multimeter to check voltage, continuity, and resistance in the wiring and components.
* Noid Light: A noid light is a simple tool that connects to the injector connector and illuminates when the injector is receiving a pulse. This helps directly confirm if the injector is receiving the signal from the PCM.
* Fuel Pressure Gauge: Essential for verifying fuel system pressure.
* OBD-II Scanner (may not be applicable): While 1995 F-150s didn't have full OBD-II, some might have a rudimentary system. A scanner could help identify any diagnostic trouble codes (DTCs).
Troubleshooting Steps:
1. Start with the basics (fuel pump, battery, etc.).
2. Visually inspect all wiring related to the injectors and ignition system.
3. Use a noid light to verify injector pulse at each injector.
4. If the noid light doesn't illuminate, trace the wiring back towards the PCM, checking for continuity and voltage.
5. If you suspect a problem with the fuel system, use a fuel pressure gauge.
Important Considerations:
* Intermittent Problem: If the problem is intermittent, it will be more challenging to diagnose. The problem might only occur under specific conditions (hot engine, cold engine, specific RPM range). Thoroughly testing everything will be key.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take the truck to a qualified mechanic. A faulty PCM is expensive to replace and should only be suspected as a last resort.
By systematically checking these points, you should be able to pinpoint the cause of your F-150's injector pulse problem. Remember safety first – disconnect the battery's negative terminal before starting any electrical work.
