* Fuel Pump itself: The pump may be failing internally. While it might pump fuel adequately once it's spinning at operating speed, it may struggle to initially overcome inertia or internal wear when first energized. This is a common cause of intermittent pump issues. Testing the pump's output pressure directly at the fuel rail (with a gauge) would be beneficial.
* Inertia Switch: Some vehicles have an inertia switch (a safety device that cuts power to the fuel pump in a collision) that can sometimes stick or fail intermittently. Locate the inertia switch (often under the dash or in the engine bay) and check it for proper operation. Try resetting it (usually involves a button to push or a switch to flip).
* Fuel Pump Pressure Sensor (or Sender): A faulty pressure sensor might send incorrect signals to the PCM (Powertrain Control Module), causing it to temporarily deny power to the pump. This is less likely given the successful operation once the engine is running, but possible. A scan tool could help reveal any sensor faults.
* PCM (Powertrain Control Module) issue: Though less likely after checking the relay and wiring, a problem within the PCM could be intermittently cutting power to the fuel pump during the initial startup sequence. A scan tool check for diagnostic trouble codes (DTCs) is essential to rule this out.
* Connectors and Grounds: Even with new wiring, check all connectors between the fuel pump, relay, and PCM. Corrosion or loose connections can cause intermittent problems. Pay particular attention to the ground connections – a poor ground can cause inconsistent power delivery.
* Low Fuel Level: Though seemingly obvious, a very low fuel level can sometimes prevent the pump from priming effectively, leading to starting issues.
Troubleshooting Steps:
1. Fuel Pressure Test: This is the most critical test. Measure the fuel pressure at the fuel rail during cranking and once the engine is running. A significant difference (or no pressure during cranking) points strongly to a failing fuel pump.
2. Inertia Switch Check: Locate and check/reset the inertia switch.
3. Visual Inspection: Thoroughly inspect all wiring, connectors, and grounds for any signs of damage, corrosion, or looseness.
4. OBD-II Scan: Use a scan tool to read any diagnostic trouble codes (DTCs) from the PCM. This can pinpoint potential electrical or sensor problems.
5. Fuel Pump Relay (again): Even though you've replaced it, make sure the new relay is properly seated and functioning correctly. Try a known-good relay to rule out a faulty replacement.
6. PCM Inspection (Advanced): If other tests are inconclusive, a professional diagnosis of the PCM itself might be necessary. This usually requires specialized equipment and knowledge.
If you're not comfortable performing these tests yourself, it's best to take your Windstar to a qualified mechanic for proper diagnosis and repair. Ignoring a faulty fuel pump can lead to engine damage.
