1998 Chevy Prizm 1.8L Misfire Codes P0300 P0302 P0141 - Fuel Pressure & O2 Sensor Diagnosis
My 1998 Chevrolet Prizm 1.8L is showing fault codes P0300, P0302, and P0141. The engine misfires during acceleration but not at full throttle, resulting in increased fuel consumption due to a rich air/fuel mixture. I've already replaced the spark plugs and performed a thorough spark system test. Injector cleaning was done using seafoam, and the engine has been treated multiple times. Fuel pressure tests show approximately 15 lbs when pulsed—within normal range. Despite these efforts, the misfire and codes persist. I'm seeking help identifying the root cause. Could it be ignition, fuel delivery, or mechanical issues? Any guidance on further diagnostics would be greatly appreciated.
Please confirm the exact fuel pressure in psi. Then, with the key off and engine off (KOEO), observe if the fuel pressure drops significantly—check for a drop of X psi within 5 minutes. A misfire can stem from ignition, fuel delivery, or mechanical issues. For P0141 (B1S2), inspect the post-cat O2 sensor heater circuit. At KOEO, verify that there is 12 volts present on the black and pink wires connected to the sensor.