backfiring
backfiring i've got a 2000 z28 a4 mac mids cat'd y slp and a lid....i'm sprayin a 125 wet shot and it has some serious spark knock at about 40mph which is right at 3000rpm (TR-6 gapped at 35) what could that be from......also when i keep on the spray ecspecially through second and a good bit into 3rd when i let off the gas and it's decelerating it backfires somethin crazy.....were talkin flames spittin outta the exhaust......is somethin wrong or is that just unburnt fuel or what i'm lost.......thanks
i try to keep my bottle pressure anywhere from 1000 to 1100 nothin more than that tho.......would timing be making it backfire like that tho? when i spray it i usually either pull it down into second or just floor and wait for it to downshift it's self but i leave it in drive and thats when it seems to backfire the most.......if i throw it in OD after i spray it its not that bad.....
Teching In
Joined: Jan 2005
Posts: 7
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the spark knock lets ya know that you need to pull some, try pulling 1 1/2 to 2 degrees and see if it helps on the knocking/backfire issue. what type fuel ru running?
Last edited by trump; Dec 21, 2006 at 10:01 PM. Reason: left out something
It is my contention that the timing issue as Robert suggested is the culpret and here is why. First, if you are picking up spark knock then you must keep in mind that the PCM is going to pull LOTSA timing out to compensate and possibly causing a rich condition that is leaving lots of unburnt fuel in the cylinders and it is passing through the exhaust and igniting while passing through and causing backfires and the light show. Second, you may want to heed their warnings and get some timing out or get some octane in the motor to see if it helps as a rich condition can tear up a motor just as well as a lean condition. Last, you didn't state what kind of kit you are using so we are unable to tell you how much timing because some kits rate the shot at the wheels while others rate it at the flywheel. Hope this helps and Merry Christmas. 
Jim C.
Jim C.
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Originally Posted by Big Geek
It is my contention that the timing issue as Robert suggested is the culpret and here is why. First, if you are picking up spark knock then you must keep in mind that the PCM is going to pull LOTSA timing out to compensate and possibly causing a rich condition that is leaving lots of unburnt fuel in the cylinders and it is passing through the exhaust and igniting while passing through and causing backfires and the light show. .....
If it were MY car, I wouldn't spray at all with KR, ESPECIALLY on a stock bottom end. If this is knock that you are HEARING, it's well past what the PCM can adjust for. If you are seeing it in software like HPT, why not fix it?
I pulled a couple of my plugs today and they all had a blue (rainbow) look to the tips of them....one was completely white, and one was even yellow near the bend of the plug, but from what i can tell it definetly needs some timing back outta it and possibly run a bigger fuel jet......any other suggestions?