Hello I'm new to this site and a new owner of an F-body, I'm a previous owner of a 97 GT Mustang. My question is that I was wondering if there was a way for me to find out whether or not I have a custom or non factory tune on my Z. My mods are in my sig and I bought the camaro with all the mods as they are. Thanks for the help.

 

The only way to tell if your tune is stock or custom would be to download the file from the PCM and let someone look at it. You would need LT1_Edit (OBD-II) or the version of Tuner-Cat OBD-II that is now sold by JET.

Or, you could send the PCM to one of the mail-order tuners, like MadZ28 or pcmforless and let them look at it.

 

Is your speedometer way off? Unless someone tuned of corrected it it will not read right. If its off, then almost for sure you have no tune or need one for it.

 

Well my speedometer seems correct but I'm not really sure and have been wondering if the odometer could be off as well. Do our f-bodies need to have the speedo corrected after a rearend gear swap? If it is not corrected should my speedometer be showing a higher MPH than I'm actually going or would I be driving at a higher MPH than the speedometer shows? Maybe what I need to do is send off for a tune cause it seems that the car could be running a little better than it is for what it has in it. I know for sure that I have a leak at the drivers side header gasket but could that affect performance? I'm gonna start to do a thorough maintanance tune up in any case and then maybe order a custom tune. BTW what is the best gasket to use for the header, I've found a copper mr. gasket and another by felpro but it's not mettalic (I don't think). Thanks for the help.

 

Yes. The vehicle speed sensor (VSS) on the tailshaft of the tranny send a pulse signal to the PCM. The PCM drives the speedo, and can not do it correctly unless it knows the rear axle ratio and the tire diameter.
Depends what gears are in the rear and what gears the PCM is programmed for. If you had a PCM programmed for the stock M6 3.42's, and the gears were actually 3.73's, the speedo would read almost 10% higher than your actual speed.
Yes. Exhaust leaks before the O2 sensors cause a "false" lean condition, and the PCM pours in extra fuel that bank of the engine doesn't really need, causing it to run rich and lose power.
Both the Mr. Gasket coppers and the Felpros will work fine. I run the Mr. Gasket coppers.

 

Have someone drive a car with everything stock and see if you both get the same readings while cruising at the same speed. If you go 60 see what theres is reading.

 

Well since you know you have 4.10's you could also get on the highway and cruise at 70mph in 3rd gear... if it was reprogrammed for the gears your RPMs should be right at/around 4100.

 

If you have a hand-held GPS, that is the best way to check your speedo.

WD

 

well I tried cruising at 70 in 3rd but my rpm's were at 4700. So now I'm not sure if I even have the 4.10's or they may be 4.11?

 

Then either you have 4.70's, or the car came with 3.23's and you have 3.73's... something like that. Just have someone look at your tune.


Here is another way you can figure out what gears you have. Jack the rear of the car off the ground, and put the car in Neutral. Then mark a straight line from the drive shaft yoke on to the rear housing. Then turn the rear tires (or rather have someone else do it) and count how many rotations the drive shaft make to one full turn of the tires. That is your rear gear ratio.

 

I think you are right I should get the tune looked at. It's makes it difficult when you purchase a performance vehicle with performance mods and you really don't know exactly what you have cause you didn't do the mods yourself. The guy I got the Z from had bought the car from his brother who was actually the one who did the mods. The guy I bought it from didn't even know how to fix the power seat harness that was unplugged. I guess he didnt want the car so that's how I got it. Although I'm kind of happy that it came with some decent mods I would rather have been the one to do the mods cause then at least I would know whats what. Thanks for the help. I'm continuing looking through the search functions to answer some other questions I have but I'll post up anything I can't get an answer to or need help with.

 

My T56 calculator shows that at 70MPH in 3rd gear (1.30:1), with stock tire diameter (25.65" on the Z-rated 245/50-16's) you would see the following:

3.42 = 4,086 rpm
3.73 = 4,457 rpm
3.90 = 4,660 rpm
4.10 = 4,900 rpm

 

With a T56 you use 4th gear.

4.10 = 4100rpm
3.90 = 3900rpm
3.73 = 3730rpm
3.42 = 3420rpm

 

Well given the correct tire size is in the tune and what not.

 

My tires are yokohama z rated 275 40 17 front and back. So if my rpms are about 4700-4800 at 70 mph in 3rd and I believe that I have 4.10 rearend would it be safe to say that the speedo and/or the odo have been corrected from the gear swap? My ABS inop light stays on constantly as well I guess from the gear swap. Later today I'll drive in say 4th gear also at 70 and check out my rpms.