P300 Random Misfire
 

Car: 1997 Eclipse GST Spyder

I recently been having a cel (reads p300) random misfire and everytime when I go WOT the car will misfire and studder. I first bought new wires and the car no longer misfire; a week or so after the car acts up again. Now I replaced the plugs with ngk iridum gapped at .28 with the new plugs and everything runs great but the cel keeps on coming back and forth --what could be the problem? I ve been searching and been reading all these possible problem; im stuck.

MODS - B16g - 550cc -- evo 3 o2 housing -- custom exhaust -- safc --injen intake -- blitz bov -- hallman mbc -- boost gauge -- air/fuel --walbro 255 -- this all i can remember but will update this as when i get home.

Thanks.

Re: P300 Random Misfire
 

I had this problem on my 97 but never really figured it out. Similar setup. Do you have a 6-bolt swap? I did.

I think dsmlink would fix it, but not sure. That is what I was going to try, but ended up selling the car first.

Re: P300 Random Misfire
 

Im still running a 7bolt. Ill look over everything again and do the basic and work my way around. I hate this stupid cell; DSMLINK will be my next step.

Re: P300 Random Misfire
 

is your bov recirculated? does this only happen when you're in boost? when it the cel comes on and off, when does it usually happen? I know that sometimes my cel would come on at times and go off when I'm cruising, which I speculate could be a faulty tps.

Just googling the the code, it seemed like it's an ignition issue. might be the coil pack.

Re: P300 Random Misfire
 

I would guess you ment a P0300 code? If so here is the Diagnostic Trouble Code Tests and Associated Procedures for that code: http://www.dsmstyle.com/photopost/data/649/78767538.JPG

Or:
http://www.dsmstyle.com/photopost/data/649/78767538.JPG

Re: P300 Random Misfire
 

Read the cel again and one of the code came back as a faulty/clogged catalytic converter; now I have been reading and this may be a cause to the p0300. I remmember having the faulty/clogged catalytic converter before the random misfire p0300. Should I replace it?

Re: P300 Random Misfire
 

Generaly a p0300 wont be caused by a plugged cat, its usually ignition or fuel related. Although it can be timing. An engine missfire can definatly will definatly plug your cat though. Cats are very delicate and anything causing your engine to run poorly can and will plug your cat. Unfortunatly a 97's computer is very primative as far as engine data is concerned. They are even harder to diagnose once you start modding them.

Re: P300 Random Misfire
 

The cel is on but I havent feeel any hesitation or misfire while in driving mode even when going WOT reaching 18psi. Ill check the car when I get home and see whats going on. No idle problem even on cold start (500-600 rpm)

Re: P300 Random Misfire
 

Interesting it says -10°C and higher, its probably colder than that here lately. Not sure what that means, but I think mine did it more often when it was cold.

Re: P300 Random Misfire
 

1st things 1st get rid of those iridium plugs. I had the same issues with those plugs.

Run the correct NGK coppers that Mitsu recomends

Re: P300 Random Misfire
 

Parked the car in the garage, checked for any vacuum leak; all intact no leak. Checked wires. Shut off the car and restart; cel went away. I don't know how but for now I'm keeping the finger crossed. Ill change back to copper if the cel comes back and recheck everything.

Re: P300 Random Misfire
 

Ok guys this stupid CEL is not going away. Checked injectors and if I remember right the third one was leaking and I replaced all injectors with 10k Evo 9 injectors; 2 days after the CEL lightens up again. It comes at any given time, at 70mph, idle, etc. Re-replaced all plugs with the coppers; gapped at 28. I just got the timing belt job done and I dont really feel any misfiring. Its driving me stupid seeing that CEL.

Re: P300 Random Misfire
 

FixeD. Injectors wasnt tight. Thanks.