* Crankshaft Position Sensor (CKP Sensor): This sensor tells the ECM where the engine is in its rotation cycle. A failing CKP sensor could send intermittent signals, allowing the car to start briefly before the ECM loses track of the engine's position and cuts the fuel/spark. This is a very common cause of a car starting and immediately dying.
* Cam Position Sensor (CMP Sensor): Similar to the CKP, but for the camshaft. A faulty CMP will lead to similar symptoms.
* Fuel Pump Relay: Even though you say you have plenty of fuel, a weak or failing fuel pump relay might provide enough power for a few seconds before failing, causing the engine to die. Try tapping the relay while cranking to see if it changes anything. (Be careful – it's electrically live!)
* Ignition Switch: This might be providing enough power for a short burst but then failing.
* Wiring Harness: Check for any damaged, corroded, or loose wiring, particularly around the sensors, ECM, and ignition components. A short or break in the wiring could interrupt power intermittently.
* Fuel Pressure Regulator: This could be leaking fuel pressure after the initial start, leading to fuel starvation. A pressure gauge test would be needed to diagnose this definitively.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Even though you've replaced components, there might be stored codes offering clues. A code reader (even a cheap OBD-II reader) might reveal relevant information. Remember that your 93 Festiva is likely too old for a standard OBD-II system, so a specific reader for that model year may be necessary.
2. Focus on Sensors: The CKP and CMP sensors are the most likely culprits given your symptoms. Visually inspect them for damage, and consider replacing them as a relatively inexpensive next step.
3. Inspect Wiring: Carefully examine all wiring related to the fuel system, ignition system, and sensors for any signs of damage.
4. Test the Fuel Pressure: Rent or borrow a fuel pressure gauge to check the fuel pressure while cranking and running.
5. Check the Fuel Pump: It may be a good idea to listen near the fuel tank to ensure the pump is running consistently while cranking. A weak pump could be the culprit.
Because you've already replaced so many parts, seeking help from a mechanic familiar with older Fords might be beneficial. They can perform more thorough diagnostics and pinpoint the problem more quickly. A mechanic will have access to tools and expertise that can help determine what's causing the intermittent failure.
