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Dont replace, upgrade
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Discussion Starter #1
So my check engine light was on for a while and i finally decided to get it read and it was P0304 (Missfire No. 4) and the primary O2. I did all new plugs and coils and new O2 and the light stayed off for about a week until i raced some guy then the light was back on when i started my car later that day. It keeps staying off for a few days at a time but then it turns back on for about a day then back off. Yesterday it turned back on after doing a 1st gear pull so the next day I got it read and it was the P0304 again but it shut off after turning my car back on later on the same day i got it read. The exhaust pops when at idle but the rpms dont jump or anything and kinda gargles when I down shift (i also have a header, 3in exhaust, and SRI). My next move is to move the coil from 4 to 2 and see if the missfire jumps and if it doesn't jump then I'm gonna get a compression with downdraft test done. I was just wondering if anyone knows what might be causing this or knows a fix. Thanks for any help.
 

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Your current ideas are good. Intermittent can be a problem to diagnose. I'd still consider fuel delivery as you addressed many ignition issues.
 

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Dont replace, upgrade
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33 Posts
Discussion Starter #4
Your current ideas are good. Intermittent can be a problem to diagnose. I'd still consider fuel delivery as you addressed many ignition issues.
So your saying it might be a bad injector? I was talking to a guy about replacing the injectors since the car has 150k on it and I've never replaced them and he said the ECU is picky when it comes to the injectors and it might make it run ruff. Idk why it would if i replace them with OEM but has anyone else ever heard of that?
 

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Not with stock. Did you reset the ECU as well. Does it idle well? How did the plugs look when you took them out? I'd get the compression checked to rule out valve issues.
 

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Dont replace, upgrade
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Discussion Starter #6 (Edited)
Not with stock. Did you reset the ECU as well. Does it idle well? How did the plugs look when you took them out? I'd get the compression checked to rule out valve issues.
Yes, after I did the plugs, coils, and O2 I unplugged the battery for a few minutes and reset the ECU. At idle the exhaust pops a decent amount but the rpms dont drop or spike. And I just switched the #4 coil into #2 and checked the spark plug on each and they both looked fine and they've been in there for about a month now. I'll attach a pic of the #4 plug. Also what brand is the stock injector?
 

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