I just ls swapped a 68 Camaro got it professionally tuned and ran fine for months and all of a sudden it backfired on startup and smoke rolled up out of the left of the hood by the windshield. It started up and will drive but the tune seems all out of wack it stays idling at 2300 rpm and won’t come down. Anybody have any ideas on what caused this and how to fix it prevent it? Looked under the hood and nothing looks abnormal. I’m running the terminator x ecm. Like I said it ran perfect for months and now all of a sudden it backfired on startup. Thanks in advance for the help.

 

whats your battery voltage?

 

I’ll check it and see. It ran fine for months and I drove it to the store and went to leave started it and backfired and smoke rolled out of the hood. Now the tune is all out of wack and idles way high. I don’t know if it messed up the o2 sensor or what.

 

If it backfired you might want to check for vacuum leaks. Sometimes when you have a backfire through the intake it will blow off lines/blow out gaskets and so on.

 

I had popping and poor idle when 2 spark plug wires burned thru to header causing a short….

2500rpm idle sounds like stuck open tb or massive vac leak.

might also reload tune w laptop.. and of log to troubleshoot.

 

I bet he blew the MAP sensor out...

 

I found out was making idle so high it blew the cap I had covering the port on the intake off now it runs fine. Still don’t know why it backfired been driving it and it has t don’t it since. Not sure what caused it. Anybody have any ideas everything looks normal.

 

I wouldn't worry about it, Mine will do it on occasion when it's sat for a few weeks or if I try to give it throttle to soon on start up. I think my issue is that it's a little lean on startup but it runs great otherwise so I just haven't messed with it. I just fire it up and let it idle for a couple minutes before I give it any throttle input.

 

Not sure how you can tell that without looking at data log[s].