Engine Backfire While Under a Load?
 

Was driving the truck this Thanksgiving weekend on I-75 and I-10 from Gainesville FL to Tallahassee FL. Several times going up hill on the interstate when the engine got under etxreme load I could hear popping and backfiring through the exhaust and from the front of the vehicle. Once it shifted out of over-drive and into 3rd it stopped. Anyone have any idea what may cause this? Had the truck retuned Christmas 2008 and hasn't done it since then until now.

My guess's are, outside air and moisture getting into the exhaust. An O2 sensor fouling, spark plugs needing to be replaced, or something with the plug wires or coil packs. Mods are in my signature.

Do you have a scan tool to check the timing when it acts up? You may have gotten some bad gas, had some KR and timing reverted to the low octane table. Did you feel a lose of power when it was popping/backfiring? How about a lose of power in normal driving?

Yes the engine was hesitating as it back fired/popped. I don't have a scan tool though. But overall no loss of hp or fuel milage, it's still a steady 19.2 on the highway. But under normal driving conditions it drives fine, the butt dyno reads the same, only as it pops/backfires does the engine seem to hesitate and lose a little power.

Anyone have any other idea's?

I hope I don't jinx you by saying that a poorly sealing intake valve will do that.

Is that a common problem on these trucks after a cam swap with stock valve's? I did my cam swap at around 11,000 miles and it has 75,000 on it now. A little off topic but I have a small oil leak now. Pisses me off that I have to pull the front engine cover to replace 2 seals that cost around 25 dollars for both, and it will tak me god knows how many hour's to do. Mine as well swap in a different cam while I am at it.

CHeck all of the plugs. Pick up some NGK TR55's. That'll only set you back ~$14 for a set.
Definitely sounds more like a miss fire than it does O2's.
O2's will definitely make it run shitty tho.

Another thing is if it has an Intake leak.

Sounds like the same problem i had. My issue were wrong o2's. It missfired and ran so rich that i was shooting 2ft flames out the side pipes. Unplugged the front o2's and it ran fine except for the SES light. I got the right o2's in last week. Truck runs 10 times better and no missfires for now

I would venture a couple of guesses:

1. Old, mis-gapped plugs, old wires, intake leak.

2. COT (Cat over temp). The extra fuel dumped to cool the cats when under heavy load could create a combustable mixture in the exhaust pipes.

3. Since you were in OD (and I presume at lower RPMs like 2-3K with the converter locked), you could be in an area of your Ve/MAF that was not tunned optimally. You could be either very lean or very rich in these areas to where your trims cannot compensate for. On the same note, your timing in these high load / low RPM cells could be off as well.

Ok thanks guys. Definately going to change out the spark plugs because I'm sure they need it. Have around 60,000 miles on them and with the tune they could be on their last leg. When I go home for the break I am going to run my buddies EFI Live on it for around 100 miles and possibly tweak a few minor things, I really just want to check the O2's because I have had problems before with the passenger side O2 not reading on the scan tool. Also, going to check for vacum leaks. We have a mechanic that rents our house that knows his stuff so we'll check the every hose, gasket etc. I just don't want it to be detonation or something harmful happening to the engine. I would hate to have go and buy a LQ9 or LQ4 he he he.