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2002 Ford F150 4.2L V6 with P0171 and P0174 Codes: Poor Performance Under Load and in Wet Conditions

Model: 2002 F150 4.2 V6 Fault Code: P0171 Posted: 2007-08-14 06:00

I own a 2002 Ford F150 4.2L V6 with persistent P0171 and P0174 OBD2 diagnostic codes. These have been present for some time, and despite multiple attempts to resolve them, the issue remains unresolved. The truck runs smoothly at idle but exhibits poor performance—jerking and bucking—especially when under load, such as while towing a lawn trailer. Performance degrades significantly in wet or humid conditions; during heavy moisture exposure, the engine becomes unstable, barely running with the service engine light flashing on and off. I've already tried several common fixes: 1. Full tune-up (spark plugs, wires, distributor cap, fuel filter, air filter) — no improvement; codes return after ~20 miles. 2. Replaced the DPFI (Direct Port Fuel Injection) system — no fix; codes reappear within 20 miles. 3. Replaced PCV valve and hoses — improved drivability, but codes return after ~20 miles. 4. Cleaned MAF sensor — performance improved noticeably, though P0171/P0174 persist and are now replaced by a new code: P0113. 5. Cleaned all visible electrical connectors, including those to the four O2 sensors — no improvement; codes return after ~20 miles. A mechanic suggested performing a smoke test to identify vacuum leaks. I'm wondering if this would be effective in diagnosing potential intake manifold gasket issues—commonly reported on this model at 115K miles. Would a smoke test detect such leaks, or should I replace the intake manifold gasket myself first? I have mechanical experience and am considering tackling the repair, but I'd like to know whether a smoke test is necessary before replacing parts. Any advice would be greatly appreciated—this truck is now nearing trade-in status due to its unreliable performance. Additional note: The current code after MAF cleaning is P0113 (IAT Sensor 1 Circuit High Input). Could this be related to wiring disturbance during the MAF cleaning process?

Related fault codes
P0171P0174
Comments (5)
Anonymous 2007-08-14 07:04

Verify the barometric pressure reading from the MAF sensor using an OBD2 scanner. Check EGR valve operation and fuel pressure with a dedicated gauge. A smoke test is recommended for detecting hard-to-find vacuum leaks, especially in older F150s with high mileage.

Anonymous 2007-08-14 09:21

How can I check the barometric reading from the MAF sensor? What tools are needed to measure fuel pressure? Is a smoke test considered a standard diagnostic method? Regarding EGR, does that mean removing it and manually testing its movement?

Anonymous 2007-08-14 10:33

Use an OBD2 scanner to check the MAF baro reading. Measure fuel pressure with a fuel pressure gauge. For EGR operation, use a vacuum pump or scan tool—especially if it's a linear actuator. A smoke test is effective for identifying hidden vacuum leaks that may not be visible during visual inspection.

Anonymous 2007-08-15 10:55

I may have overstepped after further testing—I found that cleaning the MAF sensor actually eliminated the P0171 and P0174 codes. The truck now runs significantly better. However, a new code has appeared: P0113. Does anyone know what this means or how to address it?

Anonymous 2007-08-15 11:22

P0113 indicates the IAT (Intake Air Temperature) Sensor 1 is reporting an abnormally high input. This could be caused by physical disturbance of the wiring harness during MAF cleaning, especially if the sensor was exposed or bent.