Backfire at idle and performance issues after cam install
Thread Starter
Teching In
Joined: Nov 2016
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Backfire at idle and performance issues after cam install To start off i wanted to say that i have read about 10 other "backfiring" threads and im still stuck.
Over the winter i swapped somethings on my 99 Trans Am i swapped the cam to a 218/227 .600/.600 112+2 LSA, i replaced the lifters with ls7 lifters and i put on a BBK SSI intake manifold. The car was previously Bolt Ons only and had a mail order tune. Once i put everything back together it started right up idle jumped around a bit until it learned the cam. I thought everything went well until the car started backfiring/afterfire out of the exhaust. it does it about every 10-20 sec and varies in sound from a little pop to a gunshot. As expected the car runs like crap and has a pretty big loss in power. Given the cam specs i thought it could of just needed to be tuned. So i got a tune from a well known tuner via email and the car still backfires and runs poorly. I'm 99% sure i didn't mess up the timing Cyl's #1,6 were TDC and i aligned the timing gears dot to dot. The cars manifold pressure reads 49-50 kpa at idle so i don't think its vacuum related. The spark plugs have about 5,000 miles on them and seemed in good shape when i put them back in. Today i found one of the plug wires was broken and wasn't locking onto the spark plug and i could pull the wire off with little resistance, So i replaced the wires and still no change. The car isn't throwing any codes either. I'm starting to run out of ideas here.
Over the winter i swapped somethings on my 99 Trans Am i swapped the cam to a 218/227 .600/.600 112+2 LSA, i replaced the lifters with ls7 lifters and i put on a BBK SSI intake manifold. The car was previously Bolt Ons only and had a mail order tune. Once i put everything back together it started right up idle jumped around a bit until it learned the cam. I thought everything went well until the car started backfiring/afterfire out of the exhaust. it does it about every 10-20 sec and varies in sound from a little pop to a gunshot. As expected the car runs like crap and has a pretty big loss in power. Given the cam specs i thought it could of just needed to be tuned. So i got a tune from a well known tuner via email and the car still backfires and runs poorly. I'm 99% sure i didn't mess up the timing Cyl's #1,6 were TDC and i aligned the timing gears dot to dot. The cars manifold pressure reads 49-50 kpa at idle so i don't think its vacuum related. The spark plugs have about 5,000 miles on them and seemed in good shape when i put them back in. Today i found one of the plug wires was broken and wasn't locking onto the spark plug and i could pull the wire off with little resistance, So i replaced the wires and still no change. The car isn't throwing any codes either. I'm starting to run out of ideas here.
Air fuel ratio and/or timing could be causing this. Is this a MAF tuned or SD tuned vehicle and have you examined your spark plugs to see if your running too lean or too rich?
Thread Starter
Teching In
Joined: Nov 2016
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Maf tuned. before the car was tuned it was running rich 11.7 at wot. but since its been tuned the plugs dont indicate its running rich
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TECH Addict
Joined: Aug 2005
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From: Monroe,NY
Take an infrared temp gun and check the temp of each header primary they should all be within 50-75 degrees of each other. If one of the cylinders is reading real low that cylinder isn't firing. Are you sure you didn't swap coil pack wiring from driver to passenger side.A lot of people have done that Make sure all your grounds are good and all your sensors are plugged in.
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Verdad Gallardo Thread Starter
Teching In
Joined: Nov 2016
Posts: 7
Likes: 0
It ended up being the coating came off of one spot on the ignition coil wiring and was grounding on either the coil bracket or the valve cover. It was just a little tiny piece on the bottom of wires taped it up with electrical tape and runs fine now. Thanks guys
You would have noticed the arcing if you watched the running motor in the dark! Glad to hear you reported back!