TECH TIP
F-150 Lacks Power, Rough Idle, Black Smoke from Exhaust
May. 04 2021
May. 04 2021

Vehicle: 2007 Ford F-150, 4WD, V8-5.4L, VIN 5, Automatic Transmission/Transaxle

Mileage: 242,302

Problem: This F150 was brought in for a rough idle and lack of power concern. The owner also noticed black smoke coming from the exhaust and it smelled like fuel.

Case Details: The technician was surprised that the malfunction indicator (MIL) light was off and there were no diagnostic trouble codes (DTCs) in any modules.

The owner also mentioned that the fuel rail pressure (FRP) sensor, fuel pump, fuel pump driver module (FPDM), and powertrain control module (PCM) had been already replaced. None of the new parts had fixed the issue.
 

F-150 Wiring Diagram

 

The technician connected a scan tool and noticed that the FRP sensor PID showed 20psi, but a mechanical pressure gauge showed 100psi. He unplugged the FRP sensor, and the pressure dropped to 50psi. At this point, he called ALLDATA Tech‑Assist.

The Tech-Assist consultant recommended that the technician verify that there was a 5v reference signal and a ground at the FRP sensor. If the 5v reference was low or missing, he advised unplugging any other sensor(s) in the circuit that share the 5v reference with the FRP sensor. If 5v reference was restored, then he would suspect the sensor that was just unplugged was shorted.

The technician tested the 5v reference circuit as advised and found only 0.6v on the 5v reference circuit at the FRP sensor. He started unplugging other sensors in the circuit. When he unplugged the power steering pressure sensor, the full 5v reference signal was restored to the FRP sensor. That quick test confirmed that the power steering pressure sensor was shorted internally.

Confirmed Repair: The technician replaced the power steering pressure sensor. After that, he confirmed the FRP sensor matched the actual fuel pressure and there was no more smoke and unburnt fuel coming from the exhaust. A lengthy road test confirmed that full power was restored and the idle was smooth. Fixed!

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