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2002 Pontiac Sunfire Cylinder 1 Misfire: From Specific to Random, Diagnosis & Fixes

Model: 2002 Pontiac Sunfire Fault Code: P0301 Posted: 2014-09-08 01:40

Hi everyone, I'm looking for help diagnosing a persistent misfire issue on my 2002 Pontiac Sunfire. The engine appears to have been replaced by a previous owner with a Cavalier-style engine (same displacement), which may affect the diagnosis. The problem occurs primarily when the car is cold — I can hear a distinct 'puff-puff-puff' sound, evenly spaced, which seems to originate from cylinder 1. The issue diminishes at normal operating temperature but returns under cold conditions. I took it to a local garage last week. They diagnosed a misfire on cylinder 1 and replaced the spark plugs (AC Delco, installed by me). Afterward, the OBD2 code changed to 'random multiple misfires'. They then installed a used coil pack for cylinders 1 and 4, but the random misfire persists. The garage now recommends replacing both the Ignition Control Module (ICM) and the coil packs. I'm hesitant to proceed with further expensive repairs due to my fixed income and recent forced medical retirement — I have very limited emergency funds left. I recently watched a YouTube video suggesting that 'random multiple misfires' might actually indicate one cylinder that is intermittently misfiring, rather than true random failures. This makes me wonder: could the issue still be isolated to cylinder 1, now improved slightly by new plugs? Any suggestions or diagnostic steps would be greatly appreciated. As a follow-up step, I recently ordered an OBD2 code reader on eBay so I can monitor codes independently in the future and avoid relying solely on garage diagnostics.

Related fault codes
P0301
Comments (2)
Anonymous 2014-09-08 10:47

If the misfire transitioned from specific to random, verify that AC DELCO spark plugs were used — BOSCH or discount brand plugs can cause inconsistent performance. Additionally, perform a fuel pressure test and a pressure leak-down check to rule out fuel delivery issues.

Anonymous 2014-09-08 12:19

Thanks for the reply. I confirmed that AC Delco plugs were used — I even installed them myself. A friend suggested checking the injectors, which appear to be clicking normally. I then inspected the spark plug wires and noticed that the wire connected to cylinder 1 felt loose. After removing it and giving the contact point a firm squeeze, it reseated with a clear 'click'. Since then, I don't hear the misfire during normal operation. The real test will be cold starts tomorrow. I'm cautiously hopeful this was simply a loose wire connection. Edit: The wire in question was connected to cylinder 4 (the front coil pack), so it appears that cylinder -1 and -4 wires may have been swapped incorrectly. Could the engine run with these wires reversed? This would explain why the misfire seems to shift or behave inconsistently.