Car's dying after header install....
 

OK, this is not my first post on the subject, but here goes.... after I got my Pacesetter LTs, ORY, rear O2 sims installed my car ran like crap. Backfired and stumbled. I checked all the wires and identified a cracked plug. Replaced all the plugs anyway and the car still misfires, backfires, and stumbles, almost worse than it did with the cracked plug. What the hell is going on??? I'm getting really pissed since this is my daily driver. Any ideas?

stupid question... did you check the plug gap? did you put the sims on the REAR O2's?

i have read its common for the car to act like crap after this kind of install.. have you tried letting it sit at idle and run around the block a few times.. then shut the car off.. then on a few times? i have read guys said that it needed to be cycled a few times for the computer re-learn its tables..

To be totally honest I was told that the NGK tr55s didn't need to be gapped. I had the dealer install them. I do know that they found a cracked plug, replaced all the new plugs, and they saw that one of my O2 sims (rear) was hanging down, so they zip-tied it up for clearance. The car is still missing at idle and it falls flat on it's face when I step on the gas. Runs horrible and I have no idea where to start. Plug wires and/or coil packs? :bang:

:guns: My car :bigun2:

Make sure you chaeck the gaps of the plugs, also check the wires are on good, one click for the plugs 2 for the coils (ie you should hear/feel 1 click when the wire is on the plug right, and 2 clicks on the coil) pay special attention to the back plugs, they can be a real PITA
No codes, right?
FWIW it does take some time for the PCM to learn the new configuration (seems to be about 200 miles) mine ran rich, would stumble and sputter, and reeked of gas fumes, after I did mine (seriously though about going back to stock manifolds) but after a week, it runs much better, and the gas smell is significantly less.
An old trick to find out if your plugs are firing, take a spray bottle, fill it with water, and mist some on the primary tubes, the plug that isn't firing, the water will either not evaporate, or will evaporate slower than the rest (depending if it's a completely dead cyl, or if it just fires occasionally)

It almost acts like it has a vacuum leak... does that happen often and if so, where should I start? I'm just trying to get ideas. I am going to drive it about 200miles throughout the week. I'm keeping my fingers crossed.

Get your car retuned. After installing headers you always need to get your car retuned. Like 2K2WS6TA said his car was running rich, and so is yours. It sounds odd but after doing long tubes especially cars like ours always run really rich and can cause the computer to dump so much fuel in your car that it breaks up under throttle(you won't even see any power gains,maybe 5rwhp until you get the car retuned, the car will have better response and people think they have gained power because of the better response, louder exhaust sound, and the car seems to pull to redline a hair faster do to less backpressure in the exhaust system, but that is not so). Get your car retuned and post the results( after a tune you should pick up between 20-30rwhp).

mine did the same thing. check to see if you got a good seal where the egr tube goes into the intake manifold. right behind the throttle body. if there is not a goos seal you will hear a loud hissing sound.

hope that helps

Dang, my car ran right from the git-go after new LTs and cats were installed.

How much does a tune cost typically?

Me too.

My thinking is that it is gonna be a problem with an 02 sensor over a gap issue.

A tune for a naturally aspirated car is usually between $300-$400 depending on the shop.

check the egr, with where it comes in the manifold...sounds like a vacum leak from there. It's really easy to strip the bolt that holds it in

are the front o2 sensors plugged it? That would probally make the car run like crap

i heard guys on this board say they switched the front O2 camaro sensors for rear O2 corvette sensors since they run hotter. and it seems to work..


anyone else know this trick?

Try running the car through a drive cycle: http://www.obdii.com/drivecycle.html
I had the same problem, and camaroextra suggested this. https://ls1tech.com/forums/generation-iii-external-engine/442986-wtf-car-runs-like-ass-after-lt-td-install.html
It will show any codes being thrown. Mine showed a misfire in the #5 cylinder, so I replaced the plug, which was brand new but apparently defective. Changed it and everything's fine. Just because it is new, doesn't mean it's good. Mine looked fine; no cracks or anything. Go figure.

Well, after countless hours of ripping everythign electrical off the car I located a cracked spark plug on the number 6 cylinder. Went ahead and replaced all 8 with NGK TR55s. Started the car up and it ran worse! After more searching I tested the plug wires and found that two of them were dead. Put the new wires on and the car runs like a dream. Thanks to everyone who responded. Glad I could get some help.

Thanks for coming back and telling us what the problem was.
Alot of times the OP doesn't come back and tell what the resolution to the problem was. So no one knows if they helped or not