slowmofo

iTrader: (6)

I have a 98 Trans-Am I feel likes setting on fire. It has a huge backfire issue, im not talking a few here or there, I mean like constant. So loud my neighbor came over just to chew my head off. The car has sat for three years due to a cracked block, I put another long block in it, with the same exact set up it had before. I changed nothing, and other then a oil leak the car ran strong.

I drove it up to the parts store just to scan the codes and I think my neighbors thought a gang war had broke out. My car has never received so many looks. Only code was a coolant temp sensor, which I found to be smashed and broke off Installed a brand new one, cleared the codes and now the car backfires worse then ever. It does it cold, and gets worse as it warms up, close and open loop. I can hold down the gas around 2-2500 rpms and it won't back fire.

Had it on the part store scanner real quick and my fuel trims are pegged at 25%. i need to get it on a real scanner and see what's what, but seriously my HOA is going to murder me.

I have checked and checked for vacuum leaks, and can't find anything. Not saying im missing it, just i can't find it. I was thinking of pulling the intake and reinstalling it just to be sure.

Other then a vacuum leak, what could be causing the massive fuel dump creating these shotgun backfires?

Bigbee

Check your AIR system if you still have it on there. I've heard that when the check valves on the AIR go bad it causes bad backfiring.

tsench

iTrader: (15)

backfire ehh......check your timing & tuning

89 formula350

iTrader: (8)

so it sat...... whats your fuel pressure doing? old gas still or was it driving and this just started?

redbird555

iTrader: (14)

well if it ran fine with the old engine I wouldnt look to much into the tune. Did your verify the timing chain and set were installed correctly before you dropped the motor in?

slowmofo

iTrader: (6)

Thanks for the replies guys,

I was thinking tune at first because nothing seemed to be wrong mechanically, but im lost at this point. The tune was nothing really to the engine, mostly trans stuff, but it had the air, rear o2 ect tuned out. Cams just a LS6 cam, so the stock tune was left in place.

yes the car sat for almost 3 years, only thing i did was toss a new long block in, same cam and everything. I have checked just about everything I can and its still backfiring like crazy. The cam was lined up perfectly, I checked it at least 5-6 times. prior to buttoning up the front. No Air pump, no rear o2's, no egr (ls6 intake) It does have a breather where the oil cap normally goes.

gas in the car was drained, and its all new and fresh 93. I have checked and re-check for exhaust leaks, and i pulled the intake to make sure that was not the issue. I pulled the spark plugs and 2,4,6 and 8 where a real dark sooty color. 1,3 looked perfect 5,7 were coated in fuel but were firing. I swapped injectors and it did nothing. Fuel pressure is around 58ish

I haven't really had the ability to find out what the cars doing scan wise. But I have a mechanic friend of mine driving up here today to take a look at it.

This is the 2nd engine in this car, and the first time I did this it went flawlessly. I think im sorta car savvy, but this problem is kicking my ***..

thanks for any help you guys can provide at this point.