2001 Mitsubishi Mirage Check Engine Code P304 - Cylinder 4 Misfire Diagnosis

A misfire can stem from three main areas: 1) Spark: Check if the spark plug is firing properly — inspect its appearance (wet, dry, black, tan). Swapping coil packs helps isolate this issue. 2) Fuel delivery: Use a noid light to verify injector pulse. Note: swapping injector wires is incorrect; you should swap injectors themselves. 3) Mechanical factors: Perform compression and vacuum tests to rule out mechanical problems.

When I swapped the injector wire from cylinder 1 to cylinder 4, the misfire moved to cylinder 2. This suggests that the injector for cylinder 4 is likely functional — otherwise, the misfire would remain in cylinder 4. It's also worth noting that a 'too hot' catalytic converter code was present prior to the misfire issue, which may be related.

What exactly is a 'hot cat' code? Misfires can cause catalytic converter overheating, especially if the Check Engine Light (CEL) flashes. The catalytic converter temperature exceeds normal operating range due to unburned fuel or excessive misfiring. Again: 1) Spark: Confirm plug firing — check color and condition (e.g., blue spark). 2) Fuel: Use a noid light to verify injector pulse; do not swap wires — swap injectors instead. 3) Mechanical: Check compression and vacuum levels for cylinder 4.

The spark plug is in excellent condition with a bright blue spark. After swapping the injector wire from cylinder 1 to 4, the misfire ceased on cylinder 4 and now appears in cylinder 2. The 'too hot' catalytic converter code existed before the misfire started — I don’t recall the exact code. What other diagnostics should I perform? Any advice would be much appreciated.

I believe this is a 1.8L engine. Spark plug condition appears good — is it producing a strong blue spark? Do not swap wires; instead, swap injectors to test functionality. What is the compression reading for cylinder 4? Let’s confirm: which side is cylinder #4 on? Driver's or passenger's side? I’m unclear about what a 'hot cat' code actually means.

A 'hot cat' code refers to the catalytic converter temperature being outside of normal operating range — typically due to excessive misfires. If swapping wires causes the misfire to shift from cylinder 4 to cylinder 2, and the original wire on cylinder 1 is working properly, this suggests that the injector for cylinder 4 may be functioning correctly. The movement of the misfire indicates a possible wiring or sensor issue rather than a faulty injector. Cylinder #4 is located on the driver's side.

All spark plugs are working properly and show excellent blue sparks. No signs of fouling or damage.