misfire, please help!
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Teching In
Joined: Jun 2006
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misfire, please help! I have a misfire problem that only happens at WOT after 4k rpms and on a cold start if i dont let it warm up and just drive it, it backfires and misses. I have no check engine light but it does throw a misfire code (p0300). Everytime it misfires the check guage light blinks along with the misfire. The car has longtubes, no cats, 02sims, weiand intake manifold, and a cam. It is an untuned car, But never misfired before. It has brand new plugs, plugwires, 02 sensers, fuel filter, ect.
Any help at all would be greatly appreciated.
Any help at all would be greatly appreciated.
Banned
Joined: Oct 2006
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My car has the same problem and it is a LT1 1995 Z28. I runs great up till about 3000-3500 rpms and starts cutting out , backfiring,. I have all new opti distributor, plugs , wires,MAF,Fuel pump,Coil pack? I need help too. It keeps going in and out of Open and closed loop mode as well. No codes.
The know it all's know it all
Joined: Oct 2006
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On the ls1 cars i have seen tons of valve spring failures that act like this. the small spring diameter seems to be the reason so many of them fail in street cars. On the lt1 car i would look for vacum leaks etc. In fact i would recomend doing that with both vehicles. at least pulling a valve cover to check valve springs is a piece of cake.
Are you sure you "simulated" the right O2 sensor? Seriously...did you simulate the front O2 or the rear O2?? Check for the simple solution first before you get too frustrated. I took my cats off and my bro-in law unplugged the front O2 on the passenger side instead of the rear. It's so far back on the Y-Pipe, it's easy to miss. If you have no front O2 sensor, the car will misfire as fast as a negro running from the KKK!!
The know it all's know it all
Joined: Oct 2006
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Originally Posted by 98z28m6
i simulated the rear 02s, and collinsautomotive, im pretty sure, not 100%, that the car has new valve springs.
On The Tree
Joined: Apr 2005
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From: S. Philly
Do you still have the air injection system? The air injection system supposed to lean out the mixture the first 2 minutes during warm up. If it doesn't work the car will run rich and caused back fire during open loop. Hope that help. GL\
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Teching In
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update I just put new 02 sensers in it because they're free and now it has an ses light and its throws a misfire code, and bank 1 senser 1 insufficant switching and bank 2 senser 2 insufficant switching. Any help at all again is greatly appreciated!
Last edited by 98z28m6; Nov 7, 2006 at 02:03 PM.
Teching In
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From: brick,n.j.
Hey, i have a 2001 Z28 and i also have a (code 300) random misfire. thing is i dont feel mine at idle. actually, it runs strong when i nail it. i was at work today, and i hooked up a smoke machine to a good vacuum source. preferably, something that goes right to the upper intake manifold. no smoke on the outside, but it may be an internal leak. i didnt figure it out yet, but my suspicions are leaning towrd the intake manifold gaskets. when i replace them, i'll let you know what the results were.
Teching In
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Welcome to my pain. I just had the same problem and even thought it was my coil packs going bad. Then I talked to local GURU and he said it could be a clogged injector. I pulled the fuel rail and injectors and it was nasty, lots of carb cleaner and deep creep and it runs like a champ. Took about a weekend between football games and races. Its not fun but I might be worth a shot for you to check it out.