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Misfire in 5 out of 6 Cylinders with P0301-P0305 and P0174 on 2000 Mercury Mystique

Model: 2000 Mercury Mystique Fault Code: P0300 Posted: 2016-05-02 11:38

I was driving home and noticed the vehicle running roughly, especially during acceleration. The roughness eased when RPMs were steady. Upon arriving home, I checked the diagnostic codes and found P0301, P0302, P0303, P0304, P0305 (misfire in cylinders 1-5), along with P0430 and P0340 (CMP sensor circuit fault). I replaced the Cam Position Sensor (CMP) and inspected its electrical connector. After clearing the codes, I took a test drive—the misfiring persisted, though less severe than before. Upon returning home, the only remaining code was P0174, indicating a lean condition in Bank 1. The engine still runs rough and I can hear misfires clearly. Despite replacing the CMP sensor, the issue remains unresolved. I'm seeking advice on potential root causes—such as fuel delivery issues, vacuum leaks, or MAF sensor problems—and whether live data (like fuel trims, ECT, or O2 voltages) would help diagnose this further.

Related fault codes
P0300P0301P0302P0303P0304P0305
Comments (2)
Anonymous 2016-05-02 12:43

After replacing the CMP sensor—does the P0340 code still appear? What are all the current diagnostic codes now? If only P0174 (lean bank 1) is present, consider performing a fuel pressure test, checking for vacuum leaks, and cleaning the MAF sensor. Does your OBD2 scanner display live data such as fuel trims, ECT, or oxygen sensor voltages?

Anonymous 2016-05-02 16:13

After replacing the CMP, only P0174 remains. I plan to check for vacuum leaks and clean the MAF sensor. However, how do I perform a fuel pressure test? Is special equipment required? Also, my scanner does not support live data display.