LS Backfiring issue
 

Hi guys, here's what I have: Stock bottom end 6.0, 241 heads, new ls7 lifters, new trays, stock rocker arms, custom comp cam. New Crank and cam gear, and new timing chain. I have stock pushrods (I know I need different ones with the cam-more on that in a second) ls6 intake, base tune by Mike Noris motor sports.
So, after starting with the new cam, ran great for 1:30 and I shut it off. Went to start it up after 30 minutes or so, and it started backfiring through the exhaust. Never did it in startup or while running, all the pushrods were straight, all valves checked out (applied air into the cylinders to check for leakage through intake or exhaust valves) Prior to this, the car started and ran fine.

I'll post both the old and new cam specs in comments. Thanks all!

New Cam specs
http://i240.photobucket.com/albums/f...E108629509.png

Old cam specs
http://i240.photobucket.com/albums/f...757695D3AA.jpg

Too much lifter preload. It can be off by a smidge, and cause this.

If everything mechanical with the valvetrain checked out ok my first guess would be the cam pulse is missing from either the sensor being bad or the wiring has a problem but they will usually eventually start if this is the case if you keep cranking.

So I found the issue.. the wires were crossed in an coil extension harness I got to relocate the coils. I never thought to look there since it ran fine on initial setup.

Thanks for the follow up. All too often, threads like this die off with no explanations.

Yeah I was completely dumbfounded by it. I don't get how it ran for a minute and half, and then the next time I started it, it was popping and backfiring. Would've saved me hours if I'd have started there...lol