Backfire

[taguru]

2001 TA. Just installed edelbock ported by lingenfelter heads, comp cams 230/234 600/601 cam, comp cams gold rockers, 3000 stall converter, headers, magnaflow exhaust. Downloaded repository tune, broke in the cam, adjusted idle. Everything seemed fine. Drove from Gainesville, Florida to Sebring Florida for work. No problems. Started tuning the ve and maf and developed a backfire. It started out just at idle and seemed to have no effect on acceleration. Over a period of an hour or so it seemed to backfire more and more at idle and acceleration did not feel as smooth. Pulled it in to the garage and noticed a small fuel leak at quick connect to fuel rail. Put on new quick connect, road tested, still backfiring. Did a smoke test, no leaks. New to tuning and unable to read the scan log well enough to determine problem. Any suggestions? I haven't pulled valve covers yet. Not hearing any valvetrain noise but I did use comp cams pushrod length checker to order correct pushrods and have not double checked clearance and torque since initial install.

[taguru]

One other thing that I should probably mention is that i did install the previous tune that was installed prior to the backfire and it still backfired. Just noticed rear main seal leak from the rear main seal I just replaced during stall converter install. Yaaay!

[blownbluez06]

Before reading your second post, I was going to say don't make the mistake of assuming the problem's in your tune. Putting your old tune in proved it. To identify what cylinder is causing the problem, disconnect one injector at a time and discover which cylinder is your problem cylinder. Then take a good look at your rockers because it sounds like you've got something holding a valve open. If they're adjustable, make sure you're on the base circle of the cam and readjust them if needed. If it's backfiring out the exhaust, focus on the exhaust rocker. If backfiring in the intake........

[Scotty7751]

That cam is decent sized. Stock bottom end? Oversized valves in the head? Did you notch pistons for valve clearance when you pulled the heads? Might do a leakdown or compression test. Could have tapped a valve or if the rockers were a little tight you could have burnt a valve or the rare chance a lifter roller hung it could have messed up a lobe on the cam.

[taguru]

Turned out when I was checking for zero lash I was just outside of the base circle. Rechecked them correctly this time, ordered new pushrods, problem solved. Runs great now.