Cylinder #3 misfire

[explicit.muscle]

I got back from a 4 day road trip, got in my car, drove it for about 25 miles, and now its giving me a cyl#3 misfire. I put my diagnostic tool on it and it gave me a P0303 code. Any ideas? We Just had a tropical storm come in last night here in south texas, so im thinking that something may have gotten wet under the hood.

[MTZI30]

Probably a bad ignition coil. Pretty common on quite a few cars. Repair isnt too hard.

[tigersharkdude]

IMHO its probably a coil

[loystock]

You are lucky to get a cylinder-specific trouble code. Most of the time, you just get a generic misfire code. To verify if it's the Ignition Coil #3, you can swap coils 1 and 3 and see if the problem moves to cylinder 1. You might as well check the condition of the spark plugs.

[explicit.muscle]

well so far i only had the problem that one time. im guessing the connection to the coil may have gotten wet, but then dried up. it did rain like 6" in 2 hrs, and i was driving in the middle of the storm. what i thought was wierd was the check engine light was flashing, then would go away, and then it would come on steady.

[loystock]

Flashing CEL indicates possible damage to 3-way Catalytic Converter.

[tigersharkdude]

not down right disagreeing with you loystick but my buddy who works at nissan told me that the flashing CEL was multiple cylinder misfire.

If it does actually stand for the cat, I think I am going to replace mine. Mine has flashed at me on several occasions, but by the time I get to a parts store it has turned off. and when I check it there is nothing there

[loystock]

not down right disagreeing with you loystick but my buddy who works at nissan told me that the flashing CEL was multiple cylinder misfire.

If it does actually stand for the cat, I think I am going to replace mine. Mine has flashed at me on several occasions, but by the time I get to a parts store it has turned off. and when I check it there is nothing there

There is nothing to disagree about, “Tiger.” You are right that a flashing CEL indicates multiple cylinder misfire. And in behalf of NICO, we appreciate the help you give to club members. You are a great contributor to this forum.

Maybe I am not clear enough on what I said about possible damage to 3-Way Cat. It does not mean that the ‘cat’ had been damaged.

When the CEL is flashing, it is warning you that there is a possibility of 3-Way Cat damage due to multiple cylinder misfire. During misfire condition, unburned fuel goes to the O2 sensors and ‘cats.’ So if the problem persisted, O2 sensors performance may be impaired and fuel can accumulate in the cats and eventually ignite, melting the precious metals inside. Depending on the damage sustained by the cat(s), you can have code P0420/0430 (3-Way Cat Efficiency due to inability to store O2) or even choking the engine or backfiring and other cat-related problems.

The ECM normally uses Two-Trip detection logic to turn on the CEL (the abnormality has to occur twice before the CEL comes ON). However, in case of multiple cylinder misfire, the ECM uses Single-Trip logic and flashes the CEL to indicate possibility of damage to the ‘cat.’ If the level of misfire goes down (less possibility of damage to ‘cat’), then the ECM switches the CEL to STEADY ON. And if the misfire eventually goes away after numerous ECM sampling, then the CEL turns OFF and the fault is cleared.

This was what probably happened to the OP’s car. Water ingestion in the engine compartment caused the multiple cylinder misfire so the ECM blinked the CEL. The misfire level then went down so the CEL switched to STEADY ON. The water eventually dried up and the ECM, after several sampling, turned off the CEL and cleared the fault.

To the OP, I recommend that you check the condition of the bottom engine cover and splash guards.