Effing random misfire

[JDMazdaFamilia]

So my car has been getting random misfires since I turbo'd it (about a year). I'm using an eBay 50 trim with 2.5 piping fmic and an MSP ecu. My car misfires so little often and so random that I can't catch what it is.. I've replaced plugs, I have a wideband it's steady 14-15 all day until it misses ofcourse. My boost gauge reads 20inHg vacuum all day as well. My fuel trims stay in the sweet spot under + or - 10. My MAF gives proper voltage from idle all the way to WOT, my o2 sensor is new and gives proper signals as well. Ive observed fuel curve at the injectors, all checks out fine. I've tightened up all my couplers. I have the mesh screen taken out of the maf so it's not restricting air as I have it relocated. I was wondering if the maf relocation or the screen taken out can cause it, also I don't have the air temp sensor plugged into the intake I just have it vented to atmosphere so not sure if that makes a difference? I don't want to replace coil packs and that not be it, and I'm not convinced its coil packs since it does it so little often but it's very irritating

 

[tweety2300]

Is your afr 14-15 under boost?

 

[CHIQLES]

have you cleaned the coil packs and checked the springs to see if they are making good contact at both points?

 

[JDMazdaFamilia]

Tweety no afrs are only 14-15 at cruising speeds as soon as I go into boost it reads 10-11. And no I haven't tried cleaning the coil packs and checking the springs not sure on how to do that. I forgot to mention that I've done multiple compression tests too all with good results. At first I used to be able to stop making it miss by resetting the PCM, or put in neutral and tap on the gas. I did that for a while until it stopped working then I was able to make it stop by shutting the car off and turning it right back on. When that won't work ill be able to stop it by going wot immediately after I feel a miss and it'll stop right away but lately it's been lasting longer when it does it and it won't go away for a good 10 miles give and take. I also forgot to mention each time it misses its under vacuum, it's never missed in boost. It'll do it under the lightest throttle or at idle.

 

[JDMazdaFamilia]

Anyone else have any input?

 

[Installshield 2]

I know you're saying its 'not the coils'...but your description is nearly exactly what i had last year (started late spring, finally figured it out in the fall)...and in my case, it was the coils...

I had a random misfire maybe once a month at first...cruising on the highway, would feel a very quick hesitation, and it would immediately return to normal...4 out of 5 times it wouldn't throw a code...as it got real hot through the summer, it would go maybe 6 weeks between misses...then as it got colder again, it started showing up more and more...and when it would show up, it wouldn't go away as quickly...but at least would nearly always trip the code...always P0300...never anything else with it...are you getting only that code, or any for that matter?

finally, by fall with temps hanging around 50 degree highs...it would start missing on start up, and simply wouldn't stop unless i just shut the car off for a few minutes...then would be fine for 10 miles...come back...etc...

I chased it around from fuel pump/filter/sending unit, to vacuum lines, to plugs and wires...as my coils both 'checked out' at a local shop, with them even saying 'those won't do that, they'll just stop working altogether'...but that seems to be what a lot of guys have faced; the coils don't simply stop working...that simply isn't true...they do this extremely annoying occasional BS...new coils and not one problem since...and it was $80 to replace them both...

just saying...I wouldn't rule out coils...as you've obviously looked into everything else...you're simply going to run out of stuff it could be, other than a failing ecu...which is highly doubtful...

i guess with what you've already checked...its safe to say this is spark related...so if its not the coils, you're sure the crank sensor and cam sensor are ok?...it seems to me like this is triggering related...have you checked your crank pulley? No missing or bent teeth (other than the purposed gap)?...

 

[JDMazdaFamilia]

Wow man those symptoms you had seem to be the exact same ones I'm having.. In the summer it hardly ever did it at all and it would go away quick just like you said. Once it got colder it started popping up more and more. By now mine is also starting to do it on start up and it will not go away for a while. Well I've had the coils off to do spark tests and I know you can mess up some coils by doing that, can our coils mess up by grounding them out like that? Thanks a lot for the info by the way. I also noticed one time hen I had the car running and misfiring I tried to see if the clips to the coils were on right and upon touching it, it shocked me.. So I guess that indicates I have a bad ground maybe? Not sure what else it could indicate and I don't know where or how to look for that. Also I get no other codes besides the p0300. Good point I should check out the crank pulley I haven't done that. This gives me a little bit of hope before I say F it and go to standalone

 

[Installshield 2]

Mine were very much ambient temp related, it seemed at least...if it was cold out side and cold start the car...it would usually start missing immediately...but if i let the car sit in the sun in the afternoon...it would start up no problem, and i usually had 'less' problems when the engine had finally heat up...and i'd think it was gone...then it would be back that evening after work...i replaced mine before it got really cold, but i did notice some relationship with outside temp...

and yeah dude...if that thing shocked you...thats not right haha...coils internally are pretty dense with wiring, so if their resistance or something gets messed up...they'll start outputting current in all the wrong areas...maybe the connector like you noticed; while some guys have said they opened the hood in complete darkness...with the engine missing at idle...and could actually see an arc from the coil plates to the valve cover...

I'm 99% certain you just have a bad coil, man...its just a matter of when they work...they work fine, test fine, and don't do anything funny...but then out of no where they start flipping out...then start working again...etc...sucks ahah...but, yeah check that connector and see if there are any shorts, corrosion, or bad wiring or anything...maybe a wire slipped out of its pin holder?...could be as simple as that, but i would be surprised if that didn't make the problem always happen...the inconsistency, in my case at least, came from the coils themselves...

oh and not really sure about the different tests for coils...I do know many have said our stock coils are pretty bad design wise to begin with, and since it uses a wasted spark system...they wear out faster than they need to...my local repair shop 'tested' them for me, not sure what they did exactly...but the tech said they were perfectly fine...hence me chasing the problem for another month in other areas...it wasn't until i just said screw it and replaced them, as even the factory manual suggests replacement around 100k miles (i was at 150k)...and it magically disappeared completely...

 

[JDMazdaFamilia]

Yeah true I had the wire not all the way in its pin connecter once after pulling the valve cover but that made it misfire constantly so yeah like you said about being surprised if that made it happen inconsistently. I just was never too experienced with coil packs so that was my bad for ruling it out now knowing that it made random misfires for you. Yeah it definitely shouldn't have shocked me I had my hand somewhere on the coil pack without having anything unbolted so that raised flags for me.. I could see the spark when it shocked me. I probably will just replace the coils soon and see what happens. Hopefully it solves it

 

[Installshield 2]

http://www.partsgeek.com/catalog/2002/mazda/protege5/engine_electrical/ignition_coil.html

I bought the beck/arnley replacements from here...had them in 2 days with free shipping...but it looks like the price went up (mine was $85 after tax iirc) a little...but there are other cheaper options...i figured aftermarket is fine for this stuff, as even the OE units aren't intended to last all that long...

also www.rockauto.com is popular on this site, haven't checked prices there...

 

[JDMazdaFamilia]

I really appreciate all the help man thanks a lot. I'm not too worried for best price just want the best quality.

 

[tweety2300]

Mine also missed here and there before finally dieing. But mine got worse as it got hotter out. I think I went with dura last from autozone, haven't had an issue in 2years

 

[JDMazdaFamilia]

It blew? I'm pretty afraid for the misfires to do some damage since the engine only has 50k

 

[tweety2300]

No one of them just up and quit, car would run but not well enough to drive