2002 Chevy S-10 4x4 (S-14) P0300/P0302/P0303/P0314 Misfire Diagnosis at High Speeds Over 50mph
Hello, I'm experiencing recurring misfires in my 2002 Chevrolet S-10 4x4 (also known as the S-14), which only occur when driving above 50 mph. The check engine light flashes shortly after exceeding this speed and then pauses for about 70 seconds before flashing again—this cycle repeats with a brief 1 to 3 second pause between flashes. I visited an auto parts store (O'Reilly) and they retrieved the following OBD-II diagnostic codes: - P0300: Multiple cylinder misfire detected - P0302: Misfire detected in cylinder #2 - P0303: Misfire detected in cylinder #3 - P-than 50 mph, with no noticeable stalling or jerking. I have an OBD-II scanner and performed three separate checks over the past week. In each instance, cylinders #4, #6, and #7 showed a single misfire event—but no corresponding fault code was stored for those cylinders. The P0302 and P0303 codes did not appear during these tests. This leads me to suspect that the Powertrain Control Module (PCM) may have incorrectly logged the misfires—possibly mistaking cylinder #4, #6, or #7 as #2 or #3 due to a software glitch or sensor interference. The truck has over 230,000 miles on it and consistently idles roughly with noticeable vibration. I've replaced every component except the engine itself—including ignition coils, spark plugs, fuel injectors, and wiring harnesses—while maintaining stock configuration. A new PCM was recently installed due to intermittent stalling issues when accelerating or while driving at high speeds. The replacement unit is a certified GM part directly sourced from the original dealer. The engine runs smoothly under load and maintains decent fuel efficiency. No stuttering occurs during the misfire flash, and the catalytic converter remains intact—no red glow, no clogging, and all wiring and sensor connections are in good condition. Given that the PCM was recently replaced and the fault codes only appear at high speeds, I suspect a potential internal fault within the new PCM. Despite not showing P0506 or related fuel system errors, the misfire pattern is consistent with faulty cylinder detection logic. Any insights or suggestions on how to diagnose or resolve this issue would be greatly appreciated—especially for a 2002 S-10 V6 Vortec engine with over 230k miles?
I incorrectly stated the cylinders involved in misfiring. The PCM appears to be logging misfires in cylinder #4, #6, and #7—however, based on my testing, it was actually cylinders #2 and #3 that were experiencing the misfire events. This suggests a possible misdiagnosis by the PCM or a software glitch in its cylinder identification logic.