Bstorey02 Posted February 5, 2010 Share Posted February 5, 2010 i have an 02' wrx. i had a missfire on the number four cylinder during heavy exceleration, i changed the plugs on advice from my mechanic. changed my oil and put new plugs in about 2k miles ago, check engine light stayed off till about a week ago and now says i have number four cylinder missfire again. any ideas? Link to comment Share on other sites More sharing options...
OB99W Posted February 5, 2010 Share Posted February 5, 2010 Heavy acceleration causes higher combustion chamber pressure, among other things. That makes it more difficult for the spark to jump the plug's gap. A new plug will fire more readily, so even if there are other things wrong the problem could go away for a while. How did the #4 plug look compared to #1, 2, 3 when you replaced it? Normally I would suggest changing ignition wires if they hadn't been done recently, using only OEM Subaru for the replacements. However, assuming your WRX has coil-on-plug, it might be that the #4 coil is a bit weak. Of course, things other than ignition can cause misfire. Link to comment Share on other sites More sharing options...
wtdash Posted February 5, 2010 Share Posted February 5, 2010 MR. OB99W knows a heck of a lot more than me, so take this or leave it: Get a compression test. I had a 'missfire on Cylinder 4', did a compression test, and turned out to be no compression (OK...it was 30 vs. 170 on the one next to it). I likely have a burnt valve. That #4 cylinder runs the hottest of them all, I've read. This is on a Legacy 2.5, but a close relative to your 2.0. Good luck, td Link to comment Share on other sites More sharing options...
OB99W Posted February 5, 2010 Share Posted February 5, 2010 MR. OB99W knows a heck of a lot more than me, so take this or leave it: Thanks, but I certainly don't claim to be clairvoyant -- I did say "Of course, things other than ignition can cause misfire." ... Get a compression test. I had a 'missfire on Cylinder 4', did a compression test, and turned out to be no compression (OK...it was 30 vs. 170 on the one next to it). I likely have a burnt valve. That #4 cylinder runs the hottest of them all, I've read. ... and a leaky valve is one of them. Compression/leak-down/vacuum tests could all be revealing. I only started with ignition because the new plug apparently made a significant difference, even if only for a while. The reason I asked how the old plug looked relative to the others was that "reading" plugs can often give insight into what's going on in the cylinder, based on deposits (and their color), oil/gas fouling, wear of electrodes, condition of ceramic insulator, etc. Link to comment Share on other sites More sharing options...
idosubaru Posted February 6, 2010 Share Posted February 6, 2010 i would suspect wires (or coil on plug). i realize there are other causes, but on all the EJ NA's i've worked on cylinder misfire has been spark plugs every single time. Subaru OEM all the way on that one, I've seen brand new plug wires from the store cause not only a cylinder misfire but nearly undrivable vehicle. Link to comment Share on other sites More sharing options...
Bstorey02 Posted February 6, 2010 Author Share Posted February 6, 2010 yesterday when i drove my car the check engine light was on... I get in tonight and its off... I talked to a subaru tech tonight, he said that it could be a programming problem and the ECU needs to be flashed... I tried to turn the check engine light on tonight and it did not happen. the plugs looked pretty much the same, they had a red color to them, no one was burnt more than the other. Link to comment Share on other sites More sharing options...
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