Help! Cylinder 3 mifire on 2001 Protege 2.0 with 170,000 mi. Got it scanned at parts store and had P0301 and another code for O2 sensor. (I'm assuming O2 code is secondary to the misfire problem.) Plug is slightly wet and oily compared to other 3 plugs.Took plug out and and it looked like it was getting good spark, but changed plugs and coil just in case. Still missing on 3. Swapped coil with other coil just to make sure new one wasn't defective...still missing. Took out #3 fuel injector...looked clean. Swapped fuel injector with another one and miss stayed on 3. Checked compression and cyl 3 has about 135 psi while 1, 2, and 4 have about 145...within spec per the shop manual.

Odd thing is that when you start it up sometimes it will intermittently run fine and the miss comes and goes. But then after a short time it misses constantly. Driving it down the road it still has decent power. Could it be a computer problem? Valve? What can I check next?

Not sure if it has anything to do with it but I think the car overheated a few months ago when it lost a belt and the radiator blew...put a new radiator in it and it ran fine for a few months but now has the miss.

Sorry for the long post but wanted to try and explain what I tried so far. Any help is greatly appreciated!

 

I'm right there with you. I've checked and changed plugs, check coil packs and yes I have more miles than you but they all test the same and within specs. Cleaned the TB, MAF. Oh one thing I did do was replace the valve cover gaskets. Not an easy task for someone like me who has never tried the DIY repair option. I am now on the the PCV valve and am on day 2 of disassembling. Taking it slow so I can hopefully reassemble with no parts leftover. I love my Mazdas, but this was the most idiotic placement ever. Inside the intake manifold. Unbelievable!!! I think I may be home free, well sort of. I could not get the little bugger out to save my life only to find a screw type ring locking or holding it in. Yes I broke it. So all that said, if this works, I'll let you know.
Wish me luck.