Did Mods Now Running Terrible

Sikness

Sikness

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03 LS8 did full intake a while back and car ran fine, recently did full exhaust, 2.5" ORH, 2.5" pipe back to 2 race bullets and 2 flowmaster 40s (had to put the bullets in cause it was WAY to raspy and loud without em. when i first did exhaust the car start running crappy when u try and accelerate. if the car is under like 2500rpm and you press the gas more than about 25% it sputters and barely lurches along. but if you get it up high in rpm band (3500-4000+) u can floor it and it runs and pulls fine. i got a sct tuner with preloaded tunes (from the main guy everyone uses on here, cant remember his name off hand) and tried all three and it did nothing to help either, even tried messing with the timing and fuel with no result. sometimes when its idling it does a single little sputter every once and a while too, its weird. wondering who else has had this happen and what i need to do to fix it, its made me HATE driving the car now. please help.. if i cant figure it out im gonna sell the newly rebuilt transmission and this tuner, and put a HCI 5.0 and 8.8 in it and just be done with it :cool:
 
Could just be a coincidence, when's the last time you changed your coils/plugs? Could also be that you have an intake leak or air leak somewhere under the hood. Any codes?
 
One more question, did you also replace the catalytic converters? If not, could have clogged cats causing your issues.
 
i should have specified its been running this way for a while now, like a couple months probably, i been driving the other vehicles because of it but miss this comfortable/nice ride. ive done plugs but its been a couple years, i dont drive a whole lot of miles though. never did coils. im sure we would have put the 02s back on and there is NO cats or resonators. i been wanting to upgrade the coils, and could do plugs also. it just seemed to me it would be in the tune since is just in low rpms, but like i said i played with the tune and couldnt get any results with what i changed. think coils/plugs to start??
 
Sikness said:
think coils/plugs to start??
Click to expand...

Yes. Motorcraft only - don't use the cheap autozone brand or offbrand coils. NGK/Motorcraft plugs are fine.

Also check to see if you have a decent amount of oil in your wells, if so you'll need to do the valve cover gaskets as well (VGCs). Fel pro or motorcraft are both good options.
 
hey thanks alot for the ideas. it would have to be coincidence that i need the packs bc it started right when we did exhaust but been wanting to do plugs/packs anyway so im gonna give that a try. any other ideas anyone??
 
The only things I can think of - and this is just me are Coils/plugs or a Vacuum leak.

I don't think anything exhaust related would cause that besides clogged cats and you have no cats, eliminating that possibility. If you're going to check for vacuum leaks it might also be a good idea to clean your mass air flow sensor (MAF).
 
it could be plenty of other things, but with no codes I'd start there.... your positive you CEL bulb is working (comes on with key cycle?)
 
i clean MAF every once and a while. i had CEL before tune from the exhaust so im 95% sure the bulb works, i will look when i get home tonight to make sure tho. what about "hotter" coils? i see people say Motorcraft, but im sure there are some other brands that are still good but a little more "aggressive", still stick with MC?
 
Sikness said:
.........what about "hotter" coils? i see people say Motorcraft, but im sure there are some other brands that are still good but a little more "aggressive", still stick with MC?
Click to expand...

SEARCH my friend..... This has been discussed before, ad nauseam.....
 
well im very sorry for inconveniencing you LS4ME, half the time search doesnt help but thanks for your input guy..
 
Just stick with Motorcraft, unless you want to replace them again soon because you used crappy ones from autozone.
 
Sikness said:
well im very sorry for inconveniencing you LS4ME, half the time search doesnt help but thanks for your input guy..
Click to expand...

You didn't. I do my own searching. That way we don't end up with 100+ threads on subjects like wheels. Oh wait! We already do.
 
That's interesting you were talking about how it sputtered and runs poorly. I ran my car for about a week without cats on it. I had the front O2 sensors installed but didn't run the back O2 sensors. It would sometimes sputter on start up and felt like it had no low end torque. Also sounded pretty bad under heavy throttle (just my personal preference. I don't like raspy sounding exhausts). I did how ever have a check engine light on and a bunch of codes popped up when I didn't have the back O2 sensors installed. After getting my new cats installed it seems to run much smoother and better. Hope you get it figured out.
 
op: you probably need to find one of the basic maintenance threads as mentioned.
here is my fav one:
are you running the correct octane of gasoline all day everyday?
 
running 93 and i have all 4 O2s in their exact placement and no CEL, checked and CEL lights up on start up
 
even my mechanic thinks its really weird, thinks its electrical/computer, we scanned it at my house one day with my sct and nothing hes gonna come get it from my work today and put it on his REAL scanner and just see if anything shows up, highly unlikely but i told him to check it out and change my oil anyway LOL.
 
I'd say you have some failed/marginal coils. Misfiring is much more noticeable at lower RPM range rather than higher, or at least in my experience. And yea, Motorcraft only. Prepare to drop $400, if not more.
 
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