• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

99 gtp sluggish after mods.. please help

O

onalky87

New member
looking for some help from some L67 pros:th_biggrin2:

ok so first with a little background, 99 2dr gtp 102k miles stock with intake it went [email protected]

now after speed daddy headers(no cat)and 3.5 pulley and tune it is no faster. using the same tune as all my friends have on there gtps. mine is just as fast as theres but i went 14.3 stock when they went 14.9@94 stock now we all run 14.0 makes no sense

so far ive swapped icm with no difference and put new front o2 sensor in.... i do have some small exhaust leaks but no enough to tick or anything at idle. leaves at crossover pipe and at dp with it meets catback

car knocks anywhere from 2-4.5 on a 2nd gear pull and LTFT's are -1.5 they are 9-10 at idle which seems high

thanks for any help
 
Last edited:


Honestly that car was a freak to go 14.3 with nothing else but an intake. Now what has happened is that when you tuned it you pretty much made it just like every other GP, and without a custom tune youre running what you pretty much should be running. 1 degree of timing can be worth 5hp, so that 2 to 4.5 degrees is where you are losing power. But in the end you are right where you should be. Maybe .2 tenths quicker if you can richen it up to get rid of that KR. What are your narrowband 02 values in that pull? Ive seen it too many times where people have factory freaks and think that they should still run faster than everyone elses after modding. 1+2 does not equal 3 in modding.
 
Narrowband is in the 900 range. Ltft is -1.5 wot and +10idle stft is 0 +-3. It's just frustrating that I picked up maybeeeeeee .2 from headers and a 3.5 when everyone else picked up .8-1.0. I knew it was a freak. But I've seen many cars near by my that went 14.4 stock and now do 13.5 with my mods. Thats y I feel like I'm missing something.


The tune I have is the canned tune that my buddy has on his 98 gtp that went 14.0&98. He has a cat and I don't only difference in our cars. I have stock catback as well

Maybe my exhaust leaks r making it that slow? Ik it leaks at crossover on both ends which is before o2 sensor. Not bad u can't feel it or hear it really. But when seafoaming it smokes under good pretty good bc of it
 
onalky87 said:
Narrowband is in the 900 range. Ltft is -1.5 wot and +10idle stft is 0 +-3. It's just frustrating that I picked up maybeeeeeee .2 from headers and a 3.5 when everyone else picked up .8-1.0. I knew it was a freak. But I've seen many cars near by my that went 14.4 stock and now do 13.5 with my mods. Thats y I feel like I'm missing something.


The tune I have is the canned tune that my buddy has on his 98 gtp that went 14.0&98. He has a cat and I don't only difference in our cars. I have stock catback as well

Maybe my exhaust leaks r making it that slow? Ik it leaks at crossover on both ends which is before o2 sensor. Not bad u can't feel it or hear it really. But when seafoaming it smokes under good pretty good bc of it
Click to expand...
I would start by fixing those leaks. The 02 readings will be wrong with those leaks and the car is probably running too rich because it thinks its too lean. I would fix those leaks and relearn the fuel trims. Then see what happens. You should be a lot faster.
 


Exhaust leaks really screw with the trims.

Fix those like ^^said...and try again.

I'm willing to bet that's what is causing the "sluggish" feeling 110%.
 
How should I seal it up? Take the xover off and put silicone on it? It's not leaking bad at all bc if I never seafoamed it I would have never known it was leaking. Is there a way to test for exhaust leaks?

And nothing but 93 octane. Also my bbv broke so I was only getting 2psi Max. So I took that hose off and plugged it and left bvv venting to air and now I get full boost now (10-11psi). I don't have any vac leaks
 
Seafoam is the only way I really know of or spray a light mist of water in the TB. You can use copper RTV. If you bought a set of ebay headers the clamps they come with are ****. I would buy better ones from the autoparts store. With fuel injection precision makes the difference. You want zero leaks because thats how the PCM knows how to adjust to get the targeted AFR.
 


Those are actually the clamps I'm using. It's leaking at dp where it bolts to stock exhaust right after where the cat should be but I don't think that's an issue
 
Tomorrow I'll get copper rtv and seafoam and see what I can do. If not I'll have to convince my buddy to let me use his comp and dhp so I can email u guys the tune. It makes no sense that it has good ltft and 4kr and be so slow
 
Yea anything after the first 02 doesnt matter. One thing you should think about getting is a wideband. That 900 could be rich or it could be lean. But if youre leaking at the crossover I would put my money on lean. Also you need to get rid of the 4 degrees of KR. 1 degree of KR is worth roughly 5hp. You could be losing up to 20hp due to detonation. Also, your fuel trims should lock in at zero. That -1.5 means that its pulling fuel when you go WOT, which means its leaning the car out, which is probably causing your KR.
 


Seal V-Band with RTV...have the race pipe section and the u-bend delete section that bolts to the catback welded up...I also recommend getting rid of the flange from the catback to the backhalf of the downpipe...that way that is all one piece...you're eliminating three possible leak spots, and can drop the catback with just the v-band clamp.

Not that those will affect fuel trims because they are post o2 sensor...so get the leak on the crossover or the rear header fixed first.
 
It's not.

Like Moore said...seafoam it...figure out where it's leaking from...it'll smoke from every leak.
 
You must log in or register to reply here.
Back
Top