2008 Ford F-150 4.6L Engine P0191 Fault: Diagnosis and Fixes After Multiple Repairs

Verify fuel pressure at idle and during acceleration using a mechanical gauge—this is critical for diagnosing P0191 on the 2008 Ford F-150 4.6L engine.

I use a BTCode reader and torque app, but my fuel pressure widget shows no data. Some users report that a vacuum line disconnected from the FRP sensor can temporarily resolve P0191—this may indicate a faulty or miswired sensor. A simple fix could be possible if the issue is related to vacuum signal.

When I replaced the FRP sensor, I accidentally damaged the harness clip and re-wired it incorrectly. Could this have caused a short or misconnection that leads to stalling and P0191? Would incorrect wiring prevent the truck from starting or just cause intermittent issues?

Incorrect wiring is a known cause of P0191. Always double-check harness connections and refer to official schematics—ALLDATA.com provides detailed wiring diagrams for the 2008 F-150 4.6L engine.

I removed the vacuum line from the FRP sensor and the truck ran longer, but eventually stalled again. When I reconnected it, the P0191 code disappeared—but the truck still stalls after about 10–20 seconds under load. This suggests a deeper issue with fuel delivery or sensor function.

Check for actual fuel pressure at startup and idle conditions—this is essential to rule out mechanical fuel system failure before assuming sensor issues.

No fuel pressure reading detected even after using injector cleaner. This points to a potential fuel pump or delivery issue, though the truck starts briefly, indicating intermittent problems.

Use a mechanical fuel pressure gauge to measure pressure at startup, idle, and under load. Auto parts stores often loan out these gauges—this is a reliable way to confirm if the issue lies in the fuel system or sensor readings.

First startup data: coolant temp 19°C, intake pressure 53 kPa, MAF 23 g/s, RPM 726.8, load 90.2%, STFT 0.0%, intake temp 13°C, timing advance 12°, throttle position 23.1%, voltage 13.8V.

Second startup data: coolant temp 19°C, intake pressure 48 kPa, MAF 20.6 g/s, RPM 1251.8, load 50.6%, STFT 0.0%, intake temp 13.0°C, timing advance 5.0°, throttle position 20.4%, voltage 13.3V.

It would be helpful if users could upload screenshots of diagnostic data or sensor readings for easier troubleshooting.

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I removed the fuel filter and had a friend turn on the ignition—fuel pressure was present at the pump. I blew out the filter with a compressor and reinstalled it, but the truck still stalls. No fuel pressure reading appears in the torque app. I suspect the FRP sensor is faulty, as there's suction visible on its vacuum line. I’m going to replace it today.

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I installed a new FRP sensor with no improvement—still no fuel pressure readings. I cleaned the throttle body and disconnected all motor connections, then reconnected them after cleaning. The issue persists. I’m now considering that this truck may have a deeper mechanical failure or faulty wiring.

Use a mechanical fuel pressure gauge to verify actual fuel delivery—this is the most reliable way to diagnose P0191 on a 2008 F-150 4.6L engine.