RoidedSS

Background:
Recently, my ls1 #6 cylinder cracked and water basically mixed with the oil and got everywhere. Upon removing the engine, the water-oil mix came out of the intake manifold and exhaust manifolds along with the y pipe. I dropped in a new lq9 and swapped everything over to the new block. We got the car running a few days ago and there are no lights on, everything sounds good, no missfires etc.

Issue:
After breaking it in for 2 or 3 days I decided to get on it in first gear and the car backfired hard, there was a loud pop and then the car itself stalled. I pulled over checked under to make sure there was no oil etc and say the y-pipe popped loose. So I started it back up and drove it home with open headers, reattached it and it has driven fine for the past 2 days. However, I just got on it again and the same thing happened, backfire, pop then stall. Started it back up and drove home.

Question:
Would going up the extra .3 liters affect the original tune done by Speed Inc., and need to get retuned, or could that oil-water mix have been blown into the muffler where it is now trapped and causes too much back pressure which would mean I would need to get a new muffler. The muffler is a flowmaster 40 series. Or does anyone else see any other issues. The car runs great driving around etc, but has this issue once it sees 6k RPM's

Gray Ghost Silverado

iTrader: (1)

You have cats? Plugged cats will do that. Essentially you should re-tune it. A lot has changed.

Also make sure all of your intake plumbing is tight. That will also cause similar issues.

RoidedSS

Cats are gone along with all the emissions stuff (egr and air). I just checked the intake plumbing and everything seems to check out. I'll just baby the car until I can get it into Speed Inc. again. I gotta ask though, why would the intake plumbing cause backfire issues and popping?

Gray Ghost Silverado

iTrader: (1)

I assume that the car is running on a MAF tune, therefore if you have an air leak after the MAF, that can skew fueling coefficients all over the place because the amount of air entering the engine is different than what the MAF is reading.

Good that you don't have cats.

It almost sounds as if the car is lean popping. If there's any way you can send me a log whenever you get the car to re-tuned, I'd like to have a look at it.

Stock cam and springs? Springs could cause that as well, and so could the intake if it isn't sitting correctly on the cylinder heads which would create an air leak around the intake gaskets. It's highly improbable, but just stuff to check.

RoidedSS

thank you for the info, that was really helpful. I have to call Speed Inc. to try and schedule a re-tune, however, it's probably going to be a bit of time before I can get it there since they are usually extremely busy. the lq9 received 243 heads and a 2004 zo6 cam, so the lift on it is .551/.549 I believe. The springs are good to .575

I will actually try another set of injectors and while i'm there, make sure there isn't any noticeable leaks around the intake while the car is running

Gray Ghost Silverado

iTrader: (1)

Smoke test the intake. And yank the valve covers if you haven't found the problem in one of the other things to inspect springs. That's what I'd do.

EricYJ-TA

iTrader: (10)

Smoke test? Explain?

Gray Ghost Silverado

iTrader: (1)

With a smoke machine, ram the hose down the throat of the intake and tape it for a seal, look for smoke coming out the bottom or top of the intake.

litle88

iTrader: (20)

You still need a tune bud, stop getting on it. Your timing is going to be different so just take it to them. Then see what's up. Just my .2

RoidedSS

i stopped driving it so i don't hurt anything. It's just a precaution, but I'm hoping I can get a retune without pulling out $500 again. Tomorrow I'm going to put the other injectors in and then plug in my programmer to read the timing etc. I'm no tuning expert so I won't mess with it, I just want to see if it will be where it should be, or if it's off at all.