misfire on cyl 4 (1 Viewer)

[Jetboy]

So I've never had a problem with this vehicle before. It has rained for about a week straight. Two days ago I fired up the 4runner (96 Limited 3.4l auto 4x4) and it was stumbling. It still ran, but there was a clear misfire. So I took it to the grocery store and back. It would run better at higher rpms, but not so well at idle. On the way home the check engine light came on.

So today I fired it up and went to the auto parts store. I don't have a scanner. It ran fine. Smooth as ever. Scan showed 0304 misfire on cyl 4. Not sure what would have caused it. I checked the plug and wire to cyl 4 and they look fine. I didn't replace them because it seems to run just fine.

Has anyone had this problem? If so what caused it? I have two possible culprits that I think may have been the problem. Either water causing a missed signal to the #4 injector somewhere in the engine bay, or water causing a problem with the electricity getting to the spark plug. I don't think it has to do with the MAF or a coil pack as either should cause more than one cyl to misfire, correct?

If anyone has had this problem, what was the problem? And if it was water, where was the water getting that caused the issue?

Thanks,

jetboy

 

[PigHeaded]

Probably just got some water in the distrubutor or the intake. My Tacoma stumbles and runs rough sometimes when I go through high water, but after it dries out it's fine.

 

[Jetboy]

Probably just got some water in the distrubutor or the intake. My Tacoma stumbles and runs rough sometimes when I go through high water, but after it dries out it's fine.

It felt like water in the distrubutor, but alas there is no distrubutor. It uses coil packs, however there are only 3 so each one fires 2 cylinders. I figured if it was malfunctioning it would have missed on both. It definately could have been water compromising the plug wire going to the cylinder.

 

[ToyotaDon]

If you get moisture inside the spark plug tube, either past the coil or plug wire, it will provide a path to ground with a resistance lower than the spark plug. The best thing for this depends on the amount of water/moisture in there. You can blow it out with compressed air, followed by WD-40. If there's only a small amount of moisture, WD-40 by itself should do the trick.
One thing that can help prevent this in the future is using dielectric grease where the boot seals to the plug and where the coil/boot meets the valve cover.

Note: A faulty coil can still cause a misfire on only 1 cylinder, depending on where the problem is. I've seen it happen.