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Daryl
Daryl, Shop Owner, Master Mechanic
Category: Ford
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Experience:  28 years experience, Master Mechanic
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I put new fuel pump and fuel rail sensor in 2006 Ford Expedition

Resolved Question:

I put new fuel pump and fuel rail sensor in 2006 Ford Expedition and still have problems when I scan the Expedition, the codes are P0171,P0174,P0190,P0191,P1237
Submitted: 7 years ago.
Category: Ford
Expert:  Daryl replied 7 years ago.

 

The most common cause of these codes is the fuel pump driver module, below is a test that can be done to be sure it is the problem.

 

1. Monitor the voltage across the fuel pump wires while the problem is occurring. The Pink/Black wire is the power to the pump, and the Brown/Orange wire is the fuel pump variable ground. If the voltage across these wires remains above 8 volts while the problem is occurring, replace the fuel pump.

2. If the voltage across the fuel pump wires is dropping when the pressure drops, check the circuits of the Fuel Pump Driver Module (FPDM) to narrow down the cause of the problem. The FPDM is located at the rear of the vehicle on the driver's side of the vehicle, above the spare tire.

3. The White wire at FPDM pin 5 should show battery voltage whenever the ignition key is on, from the fuel pump relay, through the inertia switch.

4. The Black wire at FPDM pin 3 is a dedicated ground for the FPDM, grounding to the frame at G403, near the FPDM.

5. The Pink/Black wire at FPDM pin 4 is power out of the FPDM feeding the fuel pump. This circuit should show battery voltage whenever the key is in the run position.

7. The Brown/Orange wire at FPDM pin 2 is the fuel pump ground circuit. This circuit is duty cycled with a ground signal from the FPDM based on the command from the Powertrain Control Module (PCM). Backprobing this circuit with a jumper wire and grounding it should result in 70+ PSI of fuel pressure if there is power to the fuel pump and the pump is good.

8. The Light Blue/Orange wire at FPDM pin 6 is the command signal sent from the PCM to the FPDM. This is a duty-cycled signal, with the PCM supplying a duty-cycle between 5% and 50% when it is commanding the FPDM to run the pump, and a 75% duty-cycle when it is commanding the FPDM to shut the pump off. If the duty-cycle is commanded between 5% and 50%, there should be exactly double that amount of ground to the fuel pump on the Brown/Orange wire. For instance, if the duty cycle on the Light Blue/Orange wire is 20%, this would be a command for the FPDM to supply a 40% ground to the pump, and if the duty cycle on the Light Blue/Orange wire is 50%, this would be a command for the FPDM to supply a 100% ground to the pump.

9. The Light Blue/Red wire at FPDM pin 1 is a feedback signal sent from the FPDM back to the PCM. This is also a duty cycle signal, with the duty cycled at 50% when everything is OK, and changing to a 25% or 75% duty cycle if the FPDM is seeing a problem.

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Expert:  Daryl replied 7 years ago.
If you do not have a way to do the testing you might remove the fuel pump driver module connectors to see if they are corroded, this is a common problem.