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2001 Ford F150 4.6L Engine Misfire with P0305 and P0174 - Diagnosis and Fix

Model: 2001 Ford F150 4.6l Fault Code: P0174 Posted: 2011-02-20 19:46

I own a 2001 Ford F150 Super Crew equipped with a 4.6L V8 engine. Recently, the vehicle began exhibiting engine misfires, and the check engine light activated. Using an OBD-II scanner, I retrieved two diagnostic trouble codes: P0305 (Cylinder 5 Misfire) and P0174 (Rich Fuel Trim Bank 2). I replaced the spark plug and coil pack for cylinder 5, cleaned the Mass Air Flow (MAF) sensor, and reset the system. However, the engine continues to misfire, and both codes persist. The OBDwiz software freeze frame data shows: - DTC: P0305 - Fuel System Status: Closed Loop, using O2 Sensors - Calculated Load Value: 29.49% - Engine Coolant Temperature: 163.4°F - Short Term Fuel % Trim - Bank 1: +3.2% - Long Term Fuel % Trim - Bank 1: -3.9% - Short Term Fuel % Trim - Bank 2: -0.78% - Long Term Fuel % Trim - Bank 2: +28.91% - Engine RPM: 717.5 The unusually high long-term fuel trim on bank 2 suggests a potential vacuum leak or intake manifold issue. I'm seeking advice on possible root causes and next steps for diagnosis, especially given the persistent misfire despite component replacement.

Related fault codes
P0174P0305
Comments (3)
Anonymous 2011-02-20 21:08

Perform a compression test and use noid lights to verify fuel injector pulse — this can help identify if the issue is mechanical or electrical.

Anonymous 2011-02-21 07:58

Given that the long-term fuel trim for bank 2 is significantly elevated, it's likely indicating a vacuum leak or intake gasket failure. These issues cause the engine to run rich in that cylinder and should be investigated promptly.

Anonymous 2011-02-21 15:01

Thanks to everyone for the input! I diagnosed the issue using noid lights — the fuel injector connection for cylinder 5 was loose and had come detached during coil pack replacement. After securing the connector, the misfire stopped and long-term fuel trim on bank 2 returned to normal. This confirms that mechanical connection issues can mimic OBD-II codes even after replacing components.