cylinder #4 Misfire, please help, out of ideas!
 

I've been having some bad misfire problems. I figured the ususal, plugs or wires, and changed both of them out. Problem seemed to be ok for awhile, and then came back. Changed the plugs again, and but the original wires back on, but it was no different. I finally threw a cel, and the code was for a cylinder #4 misfire. I then figured my problem might be the ignition coil thats directly on top of #4, so I swaped the 2 coils, and re-set the code. I threw another code later that night, and it was still cylinder #4. At this point, I'm starting to think it's the fuel injector. But I don't want to fork over the $$ if that's not it. I could use any input from anyone here with some knowledge in this area. One of my mechanic friends says it sounds like a "lazy O2 censor" but he's stumped now that the check engine light is for cylinder number 4 only. Just a couple of key points about the problem: it's virually non-existant during the day, but very noticable during night or when it's less than 50 degrees outside. It's also alot worse when the car's under a slight load (between 2500 and 3500 rpms, while trying to accelerate slowly up a hill or away from a stop sign), but will go away entirely when you downshift or when it's at higher rpm's. I was originally thinking my cat was maybe clogged up, but that should get worse at higher rpms. Any input would help. Thanks guys!

oh and by the way: I've removed all of my mods. I took off the CAI, and re-installed the stock air-box and a brand new filter. I also made sure the plugs were gapped properly, and I changed my PCV valve. Finally, I removed my rear seat and made sure the fuel pump screen filter wasn't clogged up (this was before I knew it was only cylinder #4).

When you pull #4 plug - what does it look like? Fouled? White-coated? Blued?

You can get a bad plug or wire from the factory.

The fuel inj rail is pretty easy to access - i would swap injectors with #1 and see if the problem moves. I assume you ran a bottle of inj cleaner through it and had no result.

Last possible is a sticky lifter or low compression.

(i hope this helps...)

Yeah, I'm thinking fouled plug, which means you might have an oil leak at the valve cover leaking down to the plug....fuel injector also may not be bad, but may be clogged....may want to pull it and clean it

you said you checked the gap, what did you gap them to? I've often seen mechanics gap plugs by hand and then when they go to re-install them they'll bump the electroe and close the gap off. I'd double check the gap again. If you can get us a picture of the plug it'll help.

also, what brand and model plug are you using?

I had this problem a few weeks ago. Check the coil that sits on cyl #4 and look at the plug boot on it. There is a metal spring, stretch it out a bit to make it long so that it make contact with the spark plugs. Now my car runs fine. If it was a "lazy O2" you'll get a different code, u would get a code of system to rich.

Thanks for all of the help guys. The problem is persisting and as for all of your comments and concerns: Yes, I did definately run some cleaner through the tank. I've actaully tried several brands, and concentrations. The plug (or a couple of different ones at this point) have not been fouled or burned. They have looked old once they get pulled out, and even have a little bit of soft carbon-like powder once (almost looked like exhaust build up or something). As far as compression, I checked it in cylinder number 4 and it was 180 psi. That's way more than enough. The tester I used is not a leak down tester, so I can't be sure it's holding all of that compression, but I would think it would be bad at night and during the day if that was the problem. Back to the plug: They are supposedly pre-gapped, and I verified that with a feeler guage when I installed the last ones. They are about .044 currently. These last ones I put in are just $3 bosch's, but the ones before those were $3 NGK's (sorry, don't know the exact models). As far as the coil-spring idea, I've already tried that. I was almost sure that was my problem to start with. I cleaned the crap out of both springs, and the area where it makes contact on the coil. I stretched bot of them out, and the problem continued. Then when I finally threw a check engine light, it was only for cyl. #4 so I swapped the coils and the problem stayed on #4 the next time it threw a light. I like the idea of swapping the injectors and seeing if the problem moves. The only two concerns I have are that since I swapped the coils and reset the light a second time, I haven't tripped another code so it could be awhile before I would know. My other fear/concern is that I'll have a hard time getting the injector to seal good without new seals (isn't there some kind of little o ring or something on them) or that the fuel rail wouldn't seal right against the injectors, and that's the last thing I need is a fuel leak. Any input anyone?

Can a valve spring go bad and allow the valve to float?



Hey this is my 100th post. Only took a year and a half!

i had a lil trouble with my protege like that too

exept with mine it was 2 cylinders just not running..

i took it to mazda and they told me the particular batch of my 99 protege had a service recall... some problem with the injector coils or some coil LOL.... got mine fixed alrite and it was covered by them..

maybe its that??? has ur car done 100 000Ks?? coz das when mazda told me the problem would start arising

hope it helped hehe

I'll have to look into that. I just rolled over 100k a few months ago.

I had that code after a garage installed my cams. they said it was a loose hose clamp somewhere. Unfortunatly I couldn't get a better description cause I was in toronto at the time and my g/f was taking car of it.