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2004 Ford F150 P0174 and P0306 Diagnosis: Lean Bank 2 Misfire and Ignition Issues

Model: 04 f150 Fault Code: P0174 Posted: 2016-02-10 09:06

I recently replaced the ignition coil on my 2004 Ford F150 with a 5.4L 3V engine, which improved rough idling significantly—though I still experience occasional sputtering at idle. Today, while driving home from work, I received diagnostic codes P0174 (Lean Bank 2) and P0306 (Misfire Detected in Cylinder 6). I cleaned my MAF sensor approximately two months ago, but the issue started last week when a misfire appeared on cylinder 6. I swapped the coil from cylinder 1 to cylinder 6, which eliminated the initial misfire code, but the vehicle now shows ignition coil A primary/secondary circuit faults. After driving for several days to complete a drive cycle, both P0174 and P0306 reappeared. Any insights or troubleshooting steps would be greatly appreciated.

Related fault codes

P0174P0306

Comments (9)

Anonymous 2016-02-11 08:45

Is there spark at cylinder 6? What does the plug look like visually? Also, check for vacuum leaks—especially around cylinder 6.

Anonymous 2016-02-11 13:13

I inspected the spark plug today. It was very black, indicating rich combustion or fuel delivery issues. I replaced all plugs about six months ago. The misfire began last week on cylinder 6. After swapping the coil from cylinder 1 to cylinder 6, the P0306 code disappeared, but a new ignition coil A primary/secondary circuit fault appeared. I drove for several days to complete a drive cycle, which triggered both P0174 and P0306.

Anonymous 2016-02-12 07:46

WP_20160212_07_43_38_Pro.jpg (470.65 KiB) Viewed 3288 times Attached is the spark plug from cylinder 6—shows heavy soot buildup, consistent with a lean condition or poor combustion.

Anonymous 2016-02-12 07:47

The spark plug was only about 7–8 months old. The black appearance suggests it's not the root cause of the misfire but may indicate underlying fuel or air delivery problems.

Anonymous 2016-02-12 09:30

Have you tested for spark at cylinder 6? Check for vacuum leaks—particularly near cylinder 6. Also verify fuel pressure and perform a leak-down test. Ensure you're using OEM-quality spark plugs, as aftermarket types can cause misfires or poor combustion.

Anonymous 2016-02-13 10:05

Parameter Description Diagnostic data from my OBD2 scanner: - DTC Stored: P0174 (Fuel System Bank 2 - Lean) - Fuel System 1 Status: Closed Loop - Fuel System 2 Status: Not Supported - Calculated Load: 78.82% - Engine Coolant Temp: 170.60°F - Short Term Fuel Trim - Bank 1: +3.91% - Long Term Fuel Trim - Bank 1: +14.84% - Short Term Fuel Trim - Bank 2: +8.59% - Long Term Fuel Trim - Bank 2: +26.56% - Engine RPM: 1,941.50 rpm - Vehicle Speed Sensor: 45.98 mph - Ignition Timing Advance #1 Cylinder: 27.00° - Intake Air Temp: 21.20°F - Mass Air Flow Rate: 6.99 lb/min - Throttle Position: 24.71% - O2 Sensor (B1-S1): 0.11 V, Short Term Trim: +3.13% - O2 Sensor (B1-S2): 0.58 V, Short Term Trim: +99.22% - O2 Sensor (B2-S1): 0.76 V, Short Term Trim: +10.16% - O2 Sensor (B2-S2): 0.74 V, Short Term Trim: +99.22%

Anonymous 2016-02-13 11:28

The freeze frame data confirms a lean condition in Bank 2 (P0174). Do you still have the P0306 misfire code? Please share results from your spark, vacuum leak, fuel pressure, and plug inspection tests. This will help determine whether the issue is ignition-related or due to fuel delivery/air intake problems.

Anonymous 2016-02-14 12:48

I've checked for vacuum leaks and found no visible signs—however, the P0306 misfire code persists.

Anonymous 2019-12-19 15:59

Hello, Did you ever find a solution to this issue? My 2004 Ford F150 is also showing P0174 and P0306 codes. Any advice on how to diagnose or fix it would be helpful.