misfiring under a load?

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Feb 15, 2008 | 02:00 AM

12leavu

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Racer

Joined: Feb 2006

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From: Loxley alabama

misfiring under a load?

here is exactly what is going on. the car runs fine at all times idle,WOT,city driving, ect...except in overdrive at low rpms..1200-1600 if i lightly press the gas is starts busting up. sometimes pretty bad, sometimes you can barely notice.(doesnt matter engine temp).. it hasnt thrown a code yet. i first changed the plugs and plug wires with no luck. then i installed new o2 sensors. no luck there either. any suggestions?

Feb 15, 2008 | 09:58 AM

12leavu

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Racer

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From: Loxley alabama

bump

Feb 15, 2008 | 10:30 AM

FASST LN

Drifting

Joined: Jan 2000

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From: Charlotte, NC

Just spitballing here, but maybe it could be one of your coil packs or injectors.

I would try running a bottle of Techron fuel injector cleaner through your gas tank first, since that is easy to do and only costs about $7.

And you buying premium fuel? Curious if someone from the board with a scanner is near you and could check your fuel trims under this low rpm scenario to see what is happening.

Feb 15, 2008 | 12:39 PM

12leavu

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Racer

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From: Loxley alabama

yes to premium fuel. im about to purchase hp tuners , so maybe i can diagnose the problem when i get it. i did the injector cleaner, i will run that tank empty and see if it helps

Feb 15, 2008 | 02:22 PM

~~Todd157k~~

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From: Simi Valley CA

any misfire codes? or codes at all?
did you do anything to the car before this started?

Feb 15, 2008 | 03:00 PM

12leavu

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Racer

Joined: Feb 2006

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From: Loxley alabama

Quote:

Originally Posted by Todd157k

any misfire codes? or codes at all?
did you do anything to the car before this started?

no codes as of now, been a week... actually i cleaned and oiled my k&n , so i was considering it to be a bad MAF. i do beleive however that i let it dry enough. also was running 100 octane the same day it started, (nothing new, i do everytime i go to the track i mix a 100 octane.) i went to the track, made one pass, left and drove around town all day. about 70 miles later it developed the misfire.

Feb 17, 2008 | 05:42 PM

12leavu

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Racer

Joined: Feb 2006

Posts: 366

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From: Loxley alabama

well i replaced the fuel filter/regulator. it was definitly clogged up somewhat. when i installed and cranked the car again i was getting the full 58 psi. instead of the previous 50 psi. also the pressure is still bleeding off to 0 psi, but now it is taking an hour to do so instead of 15 mins. the car is still misfiring under low rpm load. i assume the pump may be bad, a bad injector, or possibly the check valve between the tanks...however i dont believe the bad check valve would cause the misfire/studder.