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2000 S-10 4-Cylinder Misfire: P0304 Code - Diagnosis and Solutions

Model: 2000 s-10 Fault Code: P0304 Posted: 2006-12-03 14:31

My 2000 S-10 with a 4-cylinder engine is throwing a P0304 diagnostic code indicating a misfire in cylinder 4. I've already replaced the spark plugs, ignition wires, the 1/4 (cylinder) coil pack, and the ignition control module — all without resolving the issue. I performed a compression test, which showed no problems; there's no sign of head gasket failure (no oil contamination or smoke). The MAF sensor has been checked and is functioning correctly. I've also ruled out issues with the catalytic converter or oxygen sensors, as they are not triggering any related codes. No injector fault code is present, so I don't believe a faulty injector is the root cause. However, I noticed that when I let the engine sit for several hours overnight, it would run fine — but after restarting and driving about half a mile, the misfire returned. The issue has persisted for approximately one week. I've tried starting and stopping the engine multiple times, and while it runs smoothly during those cycles, it consistently fails once I begin driving. I'm at a loss as to what could be causing this intermittent cylinder 4 misfire. Any insights or troubleshooting steps would be greatly appreciated.

Related fault codes
P0304
Comments (5)
Anonymous 2006-12-03 20:00

Could a failing injector still cause a P0304 code? How do you confirm the injector is working properly? Do you have spark at cylinder #4 during misfire events? What's your fuel pressure reading? Verify that cylinder #4 is being commanded on and off by the ECU.

Anonymous 2007-04-29 22:48

Try swapping injectors to see if the misfire follows the injector. Before doing so, check the fuel rail pressure — ensure it's within normal range. A fuel pressure gauge can be found for around $40 new.

Anonymous 2007-04-30 10:35

I’d almost bet my life on a faulty injector being the cause. The 2.2L injectors in older models are known to have design flaws, including external leakage and occasional sticking issues.

Anonymous 2007-04-30 15:59

@OP: Before swapping injectors or making major repairs, try simpler diagnostics first. Bad injectors typically don't cause intermittent misfires — wiring faults might. Perform a visual inspection of all injector harnesses and connections. Check fuel pressure, but note that this is a cylinder-specific issue rather than a system-wide one. Be aware the EGR valve on late 1990s 2.2L engines is located near cylinder 4 — could this be relevant for your 2000 model? (Hint, hint.) I definitely wouldn’t bet my life on an injector being the culprit. Monitor fuel trims (STFT and LTFT) during misfire events — are they enriching or leaning? Misfires can stem from various causes: too much fuel, too little fuel, exhaust gases entering the cylinder, or wiring issues. FIRST: Always gather measurable data before making decisions.

Anonymous 2007-04-30 21:10

^ That's exactly right. I apologize — I should have emphasized that a definitive diagnosis requires actual data. You need hard numbers like fuel trims and pressure readings before jumping to conclusions.