Suspect PCM tune - can I override?

**Jglisson** · 10-06-2007, 04:15 AM

I have a 1999 Trans Am that I just bought a few weeks ago. The car has a few modifications. The transmission shifts hard from 1 -2 and 2 - 3 and my speedometer is off by 10 MPH, but I verified that I do have stock gearing.

I suspect I have a PCM tune, but hooking to a Hypertech earlier this week revealed that I DID NOT have a HP tune otherwise it would have rejected it. (I think).

My question is...with an aftermarket tuner (HP, DiabloSport, etc.) alow me to fully write over the existing tune? The only other way I can think of checking to see for sure if I have an aftermarket tune is to purchase a stock ECU/PCM off of Ebay.

**2001NBMZ28** · 10-06-2007, 10:54 AM

Just sent you an email on your other post about EGR - didn't realize you were the same person - something else to ask them about. I'm thinking the HPP3 just stores whatever tune is in the car as the "stock" tune before you upload theirs. It uploading the "stock" tune probably just means the HPP3 wasn't VIN locked. Could be wrong, been a few years since I had one.

**edcmat-l1** · 10-06-2007, 02:13 PM

The hypertech will work after a pcm has been tuned by either hpt of efilive.
You can take your car to a tuner, and he should be able to tell you if its been tuned by looking at the tables. You may just have a shift kit installed.

**Jglisson** · 10-06-2007, 03:18 PM

I guess that makes more sense than buying a stock ECU off of Ebay.

**Jglisson** · 10-06-2007, 03:19 PM

If I install a Hypertech and set my gearing to stock and my shifts to stock it may or may not override the existing settings depending on what tuning application was used.

**mrr23** · 10-07-2007, 05:47 PM

whatever changes you program it for, it will overwrite those areas.

**SStriker** · 10-08-2007, 01:28 PM

a Dealer can most likely reset your Computer to a factory tune.

**eautocad** · 10-08-2007, 03:50 PM

when i bought my car it was off by 7 mph, and shifted the same way your describing.... Does your car after 45mph tug when decelerating (coasting) without braking? If so, you neeeeeeeeeeeeeeeeeeeeeeed to fix your speedo before something bad happens.

I bought a hypertech max energy and it fixed my problem, plus gave me some tuning options I didn't have before.