Q: p0305 Misfire in Cylinder 5

asked by on January 08, 2018

I currently have an error code of P0305. I have already replaced the spark plugs and the one coil on cylinder 5, the misfire is still there. Many people have told that they can smell gas when the car is running. I replaced all in the intake gaskets in hope that there was some kind of leak. I have done a compression test and also have the freeze frame data and it will both be below.

Freeze Frame Fuel System 1 Status: Closed Loop Fuel System 2 Status: Closed Loop Calculated LOAD Value: 32.94% Engine Coolant Temp :174.20 F Short Term Fuel Trim - Bank 1: 14.84% Long Term Fuel Trim - Bank 1: 0.00% Short Term Fuel Trim - Bank 2: 3.13% Long Term Fuel Trim - Bank 2: 0.00% Engine RPM: 700.00 RPM Vehicle Speed Sensor: 0.00 MPH Absolute Throttle Position: 4.31%

Compression Test Piston 1: Dry 160 - Wet 170+ PSI Piston 2: Dry 153 - Wet 170+ PSI Piston 3: Dry 160 - Wet 170+ PSI Piston 4: Dry 155 - Wet 170+ PSI Piston 5: Dry 157 - Wet 170+ PSI Piston 6: Dry 155 - Wet 170+ PSI

My car has 100912 miles.
My car has an automatic transmission.

The fuel injector could be faulty and/or plugged and that would explain the high short term fuel trim on Bank 1 which contains cylinder No. 5. Another possibility is a vacuum leak around the intake to that one cylinder. If so, that can cause a random misfire. If the lobes on the camshaft are worn, that can cause a misfire and other inefficiencies as well. I would first check for a vacuum leak. If no leak, secondary firing patterns on the misfiring cylinder should be examined on an oscilloscope. The waveform will help narrow the potential causes to fuel versus ignition. Another possibility is the random misfire is due to intermittent faults in the injector and/or ignition components so although these components appear to be in spec during static testing, in fact they are not reliable and are later, in service, operating intermittently. Finally, the ignition and fuel driver circuits in the PCM for the misfiring cylinder could be faulty; that is the absolute last thing to test though unless you happen to have handy a known good PCM that you can substitute. If none of these possibilities pan out, you can request a misfiring diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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