Backfiring at low rpms(idle)
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You will need a tune, and probably new spark plugs now*. Get the car tuned ASAP... and I mean before you drive it again.
11 is rich at idle and cruise- your getting close to washing the cylinder walls (may already be doing it some). So change your oil also.
*I also put about 5000 miles a year on my supercharged coupe... you do not need to change the plugs after 10,000 miles (2 years). You should begin to think about it, though... probably would need to be changed in the next year anyway. But because you've been running so rich all the time carbon has probably built up quite a bit and now they do need changing. Have the mechanic save the plugs, check the electrodes for anything abnormal, if you see anything take a pic and post it here. It can tell you a lot about how your engines been doing the last 2 years.
11 is rich at idle and cruise- your getting close to washing the cylinder walls (may already be doing it some). So change your oil also.
*I also put about 5000 miles a year on my supercharged coupe... you do not need to change the plugs after 10,000 miles (2 years). You should begin to think about it, though... probably would need to be changed in the next year anyway. But because you've been running so rich all the time carbon has probably built up quite a bit and now they do need changing. Have the mechanic save the plugs, check the electrodes for anything abnormal, if you see anything take a pic and post it here. It can tell you a lot about how your engines been doing the last 2 years.
Last edited by AmateuRN; Feb 21, 2010 at 03:56 AM.
Joined: Jan 2008
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From: KY tri state area/FL keys
thanks homieg35 for the info. the car has been only running the 11 range since yesterday when the injectors,exhaust and headers were added and was not driven on the roadways. before those were added i was running in the 14.2-14.3 range which im pretty sure is normal,none the less car needs to have a tune and mostlikely ill take ur word for it, plugs changed
thanks for the help guys
thanks for the help guys
Joined: Jan 2008
Posts: 3,369
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From: KY tri state area/FL keys
how can i get it tuned w/o driving it somewhere? should i trailer it? also changed injectors back to stock,still backfiring,only ran for a few seconds
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Joined: Feb 2010
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From: DFW, Texas
Around 11.5:1 and under you really need to be concerned about bore wash. If it were my car, and I just did all those mods, I would definitely get it trailer it to the dyno. Those are significant changes, and will definitely need to be reflected in the tune.
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Joined: Feb 2010
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From: DFW, Texas
Popping on decel is a little more normal. During decel your ecu will cut the fuel, and can result in lean misfires if you've loaded up with fuel right before the decel. If it's popping at idle, but not under load, that's one thing (usually a lean idle).. If it's doing it under load, that's not good period.. Regardless, if your application is FI, you want the fueling to be spot on at all times.. If you've made changes that are going to require more fuel, or have changed injectors, get it on a dyno before you put it under any kind of load. Not having a proper tune can quickly cost you a new motor. My 2 cents.
Are the 550s smaller or bigger than the ones you are replacing? I assume bigger. If so, I don't really see how it's backfiring perse. A backfire is usually a lean condition.
It's too bad you can get it to at least idle so you can check for exhaust leaks that might make the 02s read odd.
It's too bad you can get it to at least idle so you can check for exhaust leaks that might make the 02s read odd.
Joined: Jan 2008
Posts: 3,369
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From: KY tri state area/FL keys
i added larger injectors,ive since put the stock ones back in and reset the ecu.im hoping this will work at least until i can get it to a local shop and have it tuned,i havent tried to start it yet since ive reset the ecu,as for exhaust leaks,its possible but unlikely,everything has brand new gastkets and is securely bolted.
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Joined: Feb 2010
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From: DFW, Texas
An exhaust leak will cause a rich condition, not a lean one. The o2 sensor looks for oxygen and unburnt fuel. If it senses unburnt fuel, it assumes that motor is running too rich and tells the ecu to take out fuel to compensate. If it senses unburnt oxygen, it adds fuel to compensate. An exhaust leak will cause the o2 to see unburnt oxygen, and it will add fuel even though the engine is actually probably running stoich. Here's a good read about it. Wikipedia on o2 sensors
its been a while, but are you using one step colder plugs? and did you ever figure the problem out?
I have the stillen with the 255 fuel pump and stock injectors but it backfires 1st to second and i smell faint fuel in the cab.
Im also only running 4 psi instead of 8 at WOT for some unkown reason.... i think im phuked
I have the stillen with the 255 fuel pump and stock injectors but it backfires 1st to second and i smell faint fuel in the cab.
Im also only running 4 psi instead of 8 at WOT for some unkown reason.... i think im phuked
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