Help me fix my car!

[AZ3.8Camaro]

Hey guys, this is a mostly drag racing related problem, but also a little technical.

Keep in mind I run at 3000ft elevation, and 100 temps w/humidity, so the times here are already a little slower.

Stock times for my car NA were about 15.9ish. Street tires, 2.2 60' etc. around 85 mph.

After all of my mods so far, cam, headers etc (still on stock 3.23 gears). I ran a 15.7 at also about 85 mph, same 60'. I replaced the cat, after suspecting it for some time, and ran it down to a 15.2 @ 90 mph. 2.1 60'. Much better but still slow IMO, even for the altitude.

I decided to replace the gears to better match the cam. I went with 3.73s. Went back to the track, and pulled a 2.2 60' but with an amazing 15.9 timeslip, at 80 MPH. Down 10 mph. It was hotter outside, but not that much.

I can't figure out why. I am running almost a second slower and 10 mph less with the gears? Something has to be wrong with the car here. I Dunno. THe gears whine a bit in 3rd and 4th gears, I was thinking that maybe they are too tight? I didn't notice any SOTP gain with the gears either.

Any ideas?

Also, I keep getting this weird problem where the car will kind of stutter and acelerate and slow by itself in surges. Its really wierd. It triggers the Throttle Position Sensor code, but I have replaced it 3 times already. Any ideas on this?

[Jerriko]

You did verify that they were 3.73s?

[AZ3.8Camaro]

Yup.

[Nachius]

Do you have Autotap?

If it isn't throwing codes I don't think its a misfire, but something is definitely wrong.

Other than the gears nothing at all is different with the car? Weight, Mods?

[RallyRed 98]

okay so... the stuttering and stuff, i always practice KISS... keep it simple, stupid!

fuel filter
plugs/wires
coils
ICM (my big issue, seems to go out a lot on my car at least)

i think for the TPS to be the issue i would have to look at whether or not it's going into speed density mode where it barely runs.
that's about all i can think of other than O2 or injector weirdess. does it only happen under load, or at a constant throttle position, or both?

with your gears, noise seems to just be part and parcel of the 7.5" 10 bolt. losing trap speed is a little strange though, especially to see that it was 10 mph give or take.

your density altitude and engine temps will have a lot to do with that. sometimes the low thermostats won't let the car get up to its proper operating temperature so to save a couple bucks and not have as drastic an effect, some guys just drill their stock ones. seems to work pretty well. an a/f gauge might help out here as long as you can get an accurate reading.

the thing that is most startling though are your 60s; i would figure you'd be looking at something around 2 flat or 2.1. what's your suspension/tire setup? you didn't mention anything special but i know i forget what all i have done to my car all the time.

i would personally like ot see the entire timeslip after gears, cam, etc. to perform a better diagnosis.

[AZ3.8Camaro]

I can't find any full timeslips right now.. Dunno where they all went.

My suspension is tubular LCAs, no front sway bar. Thats it.
I ran nittos on the bottle, and spun like crazy to an awful 13.8 @104 with a sweet 2.4 60', before gears. [img]smile.gif[/img] I have et streets now, so those 60's will drop.

It only seems to stutter at a constant cruising speed. I bought some used injectors that I am going to have tested and cleaned to see if it helps. How can I test my coils and ICM?

[RallyRed 98]

they are tough to test because of the nature of the circuit... it only breaks down under load so a simple resistance test won't do the trick.

this is a good question that i would like to have answered myself: how WOULD a person test that circuit, under load, without killing themselves?

will get back to you about the stutter.

[justforfun]

Originally posted by AZ3.8Camaro:
It only seems to stutter at a constant cruising speed. I bought some used injectors that I am going to have tested and cleaned to see if it helps. How can I test my coils and ICM?

Check your plugs and wires. And do a resistence test on the wires. Because they can look fine, but be broken internally.

Other than that I would look into the TPS issue.

[WickEdSix9838]

there should have been a huge SOTP difference w/the 3.73's....mine was...i'd do the KISS thing someone said...

[Camarorulz]

Your cat went bad once: maybe the new one is bad, a bad cat will do that to your car. Do the kiss thing. Chances are you're badly needing some basic maintenance. How long has it been since you ran 15.2 @ 90?

[AZ3.8Camaro]

Originally posted by Camarorulz:
Your cat went bad once: maybe the new one is bad, a bad cat will do that to your car. Do the kiss thing. Chances are you're badly needing some basic maintenance. How long has it been since you ran 15.2 @ 90?

Cat has since been gutted, no difference.

Basic maintence?!?! I am WAY beyond that. Almost eveything on the engine is new except the coils, ICM, and injectors. I am very good with cars and fixing problems, this problem is just WAY beyond anything I have seen.

I baby this car more than anything else I own.

As for plug wires and plugs.... Plugs have less than 3K on them, wires work fine. I know what a problem with the wires feels like, and this isn't it. Getting NO MISFIRE codes, just TPS...

[AZv6camaro]

Are you still running the tr6's? I would check them to make sure there not fouled since they are cold plugs. You might have some nasty deposits on them from running n/a for a while.

[AZ3.8Camaro]

Nope, I only run the tr6s when I spray.
Plugs are less than 3K miles old too.