I took my car to the dealer to find a miss. Their trouble tree said that it was my pcm so I purchased a new one. The problem is my old pcm was already tuned when I bought the car so I don't know by who or when. Now my speedometer is about 25 MPH off plus it really did not fix the miss. I am sending my pcm to madwolf but my ? is since they needed my vin # to order the pcm am I still running stock 2:73 gears? I know that their pcm's are refurbished but I felt that it would come set up for my car stock. BTW I found the miss(and i am fixing it).

 

The VIN does not contain encoding for the gear ratio. The F-body cars came with a couple different gear ratios as options. The people who refurbish the PCMs probably calibrate them with the most common gear ratio, which your car may not have.

I know the gear ratio is encoded as one of the GUx RPO codes listed on the RPO tag. I'm sure somebody has posted the gear ratio RPO codes. Of course it is possible the gears have been changed in your car, also.

I'm sure one of us could calculate your gear ratio for you if you told us your rear tire size, and your RPM in overdrive, with the torque converter locked up, at 60 MPH.

(BTW if you still have your old PCM, a PCM tuner could transfer the programming from it, to your new PCM)

 

The most common gear ratio for my car is the 2:73 which the RPO code states I have. As far as calculating the ratio I will have to get back to you with the rpm's.
Thanks

 

Why not get the old PCM back if there was really nothing wrong with it?

 

Get someone next to you at 70, note your RPM's and plug different gear ratios into one of the calculators like www.f-body.org/gears/

 

1) I had to turn in my old pcm to get my core charge back.
2) I have driven by someone at 70. Thanks for the address.

 

the vin does contain the gear ratio data,, i work at a gm dealer and if you have stock gears in the car when you hook the tech 2 to the car then to the pc it gets the factory cal file for that vin which includes speedo settings and gear ratio,,

did you get this done at a gm dealer or at a corner garage, maybe someone put a used pcm in your car??

take it back to the gm dealer if this is where you had it done, when you get a new pcm there is no vin in it and when you hook the tech 2 to the pc you must enter the vin manually and maybe the tech entered in the vin incorrectly which resulted in the wrong cal file programmed to your vehicle

 

Thanks Jay I bought it from a dealer and I installed it myself. I did not know that you had to manually enter the vin. If I get an email tune from madz28 how hard will it be for me to enter the vin #?

 

the vin doesnt really matter unless you are having the tune done at the dealer,

at the dealer we hook the tech 2 to the pc, then enter the vehicle vin # and the computer is hooked up online to the gm database and it gets the correct latest cal file for the pcm(which includes the speedo/gear data), then this is programmed to the new pcm

if you get a mail order tune they may or may not use your vin #, but it doesnt matter, the tune should have your corrected speedo values(they will usually have you fill out a worksheet with all your vehicle data)

i have software to change the vin# in your pcm if you want your mail order tune to match your vehicle vin, do you have a tunercat obd1 cable and laptop

if you just purchased this from the dealer i would drive the vehicle there and ask them to re-program it again and that the speedo is off and was correct before they sold you the pcm,, it only takes 10 min,

 

Thanks jay lt4, I just recieved my mail order tune from madz28.com so I think that I may have the problem solved. I would appreciate it if you did send me the software that you have and btw yes, I do have a laptop and cable. My email address is

jatkins9@midsouth.rr.com

Thanks for all of your help

 

Sorry, what I meant was that there is no direct translation of a VIN character for the rear axle ratio. GM's system works by correlating a VIN with the original build information for the car.

 

file sent to ya