I have missfire until i make 20 miles. after 20 miles its starts to clear and leave the missfire. i have new greddy spark plugs, but same thing was before. the car has only 45k miles, 2003 evo 8.

any idea?

 

i know you mentioned that you had the misfire before the greddy plugs but have you gapped the plugs? have you checked for any loose hoses? is the car throwing any cel lights?

 

i checked the gaps on the new plugs of corse. i had flash cell light before, but i changed the bov and that is fixed. the funny thing is, why runs perfect after 20 miles? the coils looks ok.

 

Make sure the car is completely up to temp before you romp on it. The ECU doesn't use the front 02 sensor to control the fuel maps until your engine reaches a certain temperature. So until then, it pretty much guesses, and runs pig rich.

 

is you car tuned? perhaps it has something to do with the timing down low?

have you taken a look at the MAF sensor to see if its dirty or something? perhaps a boost leak somewhere?

 

Than the issue should be constant instead of resolving it's self after 20 min. I think it's either an ECU or cold spark plug issue.

 

the car now ecuflashed to 1,5 bar peak and 1,3bar at redline, but did the same thing, when it was full stock. i have aem uego in my car. it shows rich, (10.0afr) when do missfire. same afr, when its cleared. i loged with ecuflash. its dont shows anything. no knock, only 1 or 2 knock sum.

 

Maybe the coil is starting to fail?

I just had one go bad at 67k. In my case it worked fine unless you were in full boost. It is easy enough to check if you have a friend with an evo by swapping out coils.

 

have you tried anything?

 

yes. i will try the coils next week.

 

So what you are saying is your car holds 10.0 AFR at full throttle even after it stops misfiring?

 

the aem shows 10.0 afr when its missfiring and the same thing, when dont.

 

3"downpipe back, walbro 255 pump, lower ic pipe, greddy sparkplugs., k&n air filter.
maped 1,5bar

same thing was, before the mods.

 

problem resolved. i installed my standalone ecu.

thanks guys the helps, but maybe some sensor was bad.

 

Sounds like the tune, IMO... But glad it's fixed!