Car runs weird after LT install...

**GottaHaveLS1** · 08-21-2007, 05:26 AM

So I got my LT's installed yesterday by a local shop. they put in P/S LT's and ory and some ngk tr55. When I rev it everything sounds fine, but in WOT when it's under load, the car sort of bucks and doesn't go thru the RPM's very smoothly at all. I know I could use a tune but i didn't think it would run this bad. I double checked that the plug wires all went to the right spark plug. I'll call the guy who installed everything and ask him what he thinks, but other than that i'm clueless.

**35thAnniZ28** · 08-21-2007, 05:47 AM

hmmm well you checked the plugs n wires.....what about o2's?

**0rion** · 08-21-2007, 06:09 AM

your description makes it sound like a spark issue. I see people use those types of descriptions for misfires. Could be a plug wire not on a plug or coil tightly ( should click when you push the wire onto the plug or coil) or they may have cracked the ceramic on a plug if they banged them with the headers.

The O2's like was mentioned above are another option. You can get under there and check to make sure they have them plugged into the correct locations and that there are no wires burned by the headers.

**GottaHaveLS1** · 08-21-2007, 06:37 AM

Originally Posted by 0rion

your description makes it sound like a spark issue. I see people use those types of descriptions for misfires. Could be a plug wire not on a plug or coil tightly ( should click when you push the wire onto the plug or coil) or they may have cracked the ceramic on a plug if they banged them with the headers.

The O2's like was mentioned above are another option. You can get under there and check to make sure they have them plugged into the correct locations and that there are no wires burned by the headers.

the plugs and wires seem fine but I'm gonna have my dad look at it real soon just to double. I'm going under the car right now to check out the 02's. Could this be happening from the computer relearning the exhaust? Would disconnecting the battery help at all?

**Spaz** · 08-21-2007, 06:39 AM

wait untill night or pull in to a dark garage and see if you can see sparks arking from the plug wires to the headers...

**0rion** · 08-21-2007, 08:11 AM

Originally Posted by GottaHaveLS1

the plugs and wires seem fine but I'm gonna have my dad look at it real soon just to double. I'm going under the car right now to check out the 02's. Could this be happening from the computer relearning the exhaust? Would disconnecting the battery help at all?

The hard part of these posts is determining what you're trying to describe. When you say it's "bucking" under a load that really makes me think it's a spark issue. Example. My buddy at work has a 98 heads/cam vette. He described pretty similar the same problem you're having. His came out of nowhere though, it wasn't directly after mods. His ended up being a cracked plug wire boot that had been resting on the header. The first thing I would do is look at your wires and make sure they're on good and tight, it's pretty easy during a header install to not get a wire on all the way. It's a simple thing to do to rule out the obvious first. If that doesn't fix it then I would start looking at the plugs themselves. Do you have a way to log the car? That would tell you immediately which cylinder(s) are misfiring.

**GottaHaveLS1** · 08-21-2007, 02:46 PM

Originally Posted by 0rion

The hard part of these posts is determining what you're trying to describe. When you say it's "bucking" under a load that really makes me think it's a spark issue. Example. My buddy at work has a 98 heads/cam vette. He described pretty similar the same problem you're having. His came out of nowhere though, it wasn't directly after mods. His ended up being a cracked plug wire boot that had been resting on the header. The first thing I would do is look at your wires and make sure they're on good and tight, it's pretty easy during a header install to not get a wire on all the way. It's a simple thing to do to rule out the obvious first. If that doesn't fix it then I would start looking at the plugs themselves. Do you have a way to log the car? That would tell you immediately which cylinder(s) are misfiring.

what do you mean "log the car"? I'll try looking under the hood when its dark out to see if the plug wires arc. I checked the 02's and they're connected and no wires melted on the headers. The car feels slower and doesn't rev up (under load) like it used to. It will accellerate fine from say 3500 rpms to 4000 but the sort of "bog" from 4000 to 4500. That isn't exactly what happens but it's the best way i can explain it. All the plugs and wires we can reach feel like they are fine (no ceramic broken and fully connected). I can't get my hands back to the 2 rear plugs on the passenger side.

**greatwhiteZ28** · 08-21-2007, 03:31 PM

how about the plug gaps?

**GottaHaveLS1** · 08-21-2007, 05:35 PM

Originally Posted by greatwhiteZ28

how about the plug gaps?

I didn't do anything to my spark plugs. It might have been a bad idea to assume they were gapped correctly, but i'm not sure. If they weren't right, then the guy who installed them probably would have corrected it. He seemed to know his shit real good but i'll ask him about it anyways.

I'm going down to a shop in New Haven to have it tuned. It wont get a full dyno tune but hopefully adjusting the A/F ratio and other stuff should fix the problem.

**Rob00Taws6** · 08-21-2007, 06:28 PM

Ha, how bout that, I’m from Connecticut too. Orange as a matter of fact, but there is only two people I trust working on my car. One is on Rt. 34 Rocco from Mild to wild performance, and the other of course is myself. But, I have dynatech LT headers on my trans am with there y-pipe and there high flow catalyst converters. I’m throwing a catalyst deficiency code and decided to change the plugs. I bought the car in Naugatuck with the exhaust already on the car. When I pulled the plugs on the car I found some gaped at .045 and some a .050 and others at .060 and there was a combination of NGK and AC delcos on the car. But, I changed the plugs out with AC Delco’s, iridium, gaped at .060 and the car idles better and I also noticed a big difference at higher RPM’s I know that it’s a big pain to pull plugs, but you should pull a couple, from under the car plug 8 and 7 are not to hard to get to. If your plugs were installed out of the box then there gaped to small. They should be gaped at .060

**GottaHaveLS1** · 08-22-2007, 03:43 PM

Originally Posted by Rob00Taws6

Ha, how bout that, I’m from Connecticut too. Orange as a matter of fact, but there is only two people I trust working on my car. One is on Rt. 34 Rocco from Mild to wild performance, and the other of course is myself. But, I have dynatech LT headers on my trans am with there y-pipe and there high flow catalyst converters. I’m throwing a catalyst deficiency code and decided to change the plugs. I bought the car in Naugatuck with the exhaust already on the car. When I pulled the plugs on the car I found some gaped at .045 and some a .050 and others at .060 and there was a combination of NGK and AC delcos on the car. But, I changed the plugs out with AC Delco’s, iridium, gaped at .060 and the car idles better and I also noticed a big difference at higher RPM’s I know that it’s a big pain to pull plugs, but you should pull a couple, from under the car plug 8 and 7 are not to hard to get to. If your plugs were installed out of the box then there gaped to small. They should be gaped at .060

I called the shop that put them in and they said they gapped the plugs to .060. I'm bringing the car back in tomorrow and we're gonna take it for a ride. the guy who installed it is very experienced in tuning, so he should be able to help me out.
Could a bad a/f ratio cause all this??

**0rion** · 08-22-2007, 04:08 PM

I wouldn't absolutely rule out the tune but I wouldn't think headers would throw your tune off that far. It's definitely not optimum but the car should still run just fine.

**Rob00Taws6** · 08-22-2007, 06:15 PM

Question with the bucking? When you hold the throttle at a constant RPM in neutral under no load lets say at 2000 RPM, 2500 RPM, and 3000 RPM will the RPM oscillate or will in stay steady? I’m thinking quick steady bursts up and down in a small range, when the throttle is held constant. Do you have any problem like that? Or is it only WOT under load?

**408WS6** · 08-22-2007, 07:11 PM

You might check you wiring going to your O2 sensors. Its real easy to get those too close to the headers and burn them, therefore, throwing off your fueling. Also, you really should get it retuned. Going from stock manifolds to longtubes is a pretty major change that will most certainly affect the air-fuel ratio.

**blue02Z** · 08-22-2007, 10:02 PM

when i put mine in it did not do that. are you throwing any codes? did you change your wires or stay factory?

**GottaHaveLS1** · 08-23-2007, 05:27 PM

Originally Posted by Rob00Taws6

Question with the bucking? When you hold the throttle at a constant RPM in neutral under no load lets say at 2000 RPM, 2500 RPM, and 3000 RPM will the RPM oscillate or will in stay steady? I’m thinking quick steady bursts up and down in a small range, when the throttle is held constant. Do you have any problem like that? Or is it only WOT under load?

when the car is in neutral it revs up fine and sounds beautiful. When i hold it at a certain RPM is stays constant in neutral. It is not only under WOT, if i drive the car at a 1/4 throttle to five grand in each gear I can still feel some "jerking" or hesitation but it's more noticeable under WOT. It also revs a lot slower thru the gears. There is no SES light. I checked the 02's and the wires, they are fine. I'm taking it to a shop tomorrow to get tuned up a little. I can't afford a $400 dyno tune but this guy is gonna help me out. I'll let you know how things turn out.

**GottaHaveLS1** · 08-23-2007, 05:29 PM

Originally Posted by blue02Z

when i put mine in it did not do that. are you throwing any codes? did you change your wires or stay factory?

I kept the stock wires cuz i didn't want to spend an extra $60 on MSD wires. The guy that installed everything said that putting in some ngk tr6 could help out. But i'll look into it after it gets tuned tomorrow.

**GottaHaveLS1** · 08-24-2007, 01:36 PM

So i drove 60 miles to a shop in New Haven today to get my car tuned. I paid 200 bucks for him to delete codes and tune the car (not on a dyno). the codes got taken care of but the guy couldn't completely tune the car because he said the motor wasn't getting enough fuel! So i'm going to replace my fuel filter and if that doesn't fix it then i'll have the injectors cleaned. I also noticed that one of my plug wires had a crack in it on the top. I don't think it was there until today or yesterday. I'll probably order some MSD's.

I'm so frustrated right now, everytime I buy something for my car it just leads to another problem. I just want it tuned and done with. I've spent around $1400 and the car is slower and runs pretty crappy. Do you guys have any advice????

**GottaHaveLS1** · 08-24-2007, 01:37 PM

Also, I can order MSD's for $62 plus shipping or should I just get a generic brand from napa for $55?

**0rion** · 08-24-2007, 02:09 PM

I would pay the extra and get msd wires. Right now I think you're learning lessons that'll last you a lifetime and we all have to learn these lessons. If you have the manifolds off putting on headers it's always a good idea to replace plugs and wires. How many miles are on your fuel filter? That's an easy replacement that you can do in the driveway in just a few minutes. It may feel like the car is kicking your butt at the moment but it'll get taken care of and after everything is said and done you'll be glad you did the header swap.
I'll explain why you should get msd wires. I swapped some on my truck several years ago and still had a miss I had been chasing down. I used cheap wires but when I put the wires on to me that pretty much ruled out the wires. I fought that thing for several more days trying to find the miss. One evening just after dark I had the hood up still working on it and something caught my eye. One of my brand new wires had a little tiny "hair" sticking out of the boot that was arcing to the block. I also put some wires on for someone and they bought the cheap wires. Everytime it rained their car would run like crap. I found it was the coil wire, the boot was a little loose on the coil and it was letting moisture in. Just a couple of reasons I would spend the extra $7 for MSD wires.