99' GA STOCK PCM question... [Archive] - GrandAmGT.com Forum


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07-30-2008, 12:47 PM
correct me if im wrong, but it changes as you drive and adjust to how you drive? so if i disconnect battery it should reset? because i notice if im driving to school, 90 mph the whole way there, and i gun it at a stopsign or something, it dont wanna move really, but if i drive through city for awhile, i gun it, it has a lot of bottom end.

07-30-2008, 01:21 PM
You are correct, but it takes days maybe weeks for it to adjust, it learns when to downshift, etc. Not hours, or minutes. after going 90, and gunning it from a stop it doesn't feel so fast, well cuz you're not going 90 anymore.

but stop-and-go city traffic and then you gun it, of course it'll feel faster.

if you want to test your theory, I've seen something like an in-car-g force meter, attaches to your windshield. I don't know how accurate they are, but it's something to check out if you want to test your theory. These things can estimate your quarter mile times, etc.

07-30-2008, 06:37 PM
Actually things like when it downshifts are set in the pcm and do not move. The only thing the pcm changes based on your driving habits is line pressure and delay on shifts, and some torque reduction in the engine on shifts. That is the transmission adaptive learn feature, and is solely to compensate for transmission wear based on your driving. Disconnecting the battery will not reset that either. You have to reflash the pcm.

The pcm also learns fuel trims, but those are based on O2 sensor readings and not driving habits, and they only take about a half hour to learn. You can reset those in real time with a tuner, or by disconnecting the battery for about an hour. There isn't much point though, because unless you've changed the O2 sensor or something else that affects fueling, the fuel trims will go right back to where they were before.

07-30-2008, 08:28 PM
^^ that's about what i meant, but said it wrong. all i know is after i drive a car, it downshifts sooner then later after i've had a few days on it. at first I have to floor it to downshift, and over time i don't have to press on the pedal as hard.

07-31-2008, 05:35 PM
Yeah, the actual point at which it downshifts is based strictly on throttle position and rpm and doesn't change. Only the line pressure and possibly the shift time change over time, so that could contribute to what would seem like a delay or "lag" in the shifts.

It should work opposite of how you are saying though. If you reprogram it and reset the learning in the pcm it should shift harder and faster when you first drive the car, but if you've increased the HP and torque over stock the pcm will detect that and should attempt to soften and slow your shifts over time in an attempt to save the transmission. That's why for people who have beefed up the tranny with raybestos clutches and such, it might help to occasionally flash the pcm to reset it and keep the shifts hard. iirc you have to do a full write to reset it too. I don't think a partial flash will do that. I could be wrong though, been a while since I read about that.