My PCM has a short term memory
 

After the car sits for a few hours and I start it up, all the gauges on the dash flash to there max reading, then back to a 0 rating, then go to the correct setting. For example. Tach with go to 7K, then down to 0, then up to 900 rpm. The trip meter also resets to 0. Also seems the car has to relearn how to idle. If I go on a trip and shut the car off for a short period, say to get gas or run into the store it will retain it's memory... any idea what would cause this?

Dan
99 T/A MTI programming.

It sounds like a short or improper contact. I know for a fact that when my car would do that, it was due to the battery being low. I have noticed some vehicles had either a bad contact behind the dash for the gauge cluster or the battery terminals were loose.

You either have a battery or alternator on it's way out, or a bad connection.

And since you have a 99 you will get the trip reset ...... Mine does the same when my lightweight battery gets low.

http://www.ls1camaro.net/freehosting/aug99tsb.jpg

Hmmm funny I have the same problem. I thought it was because I moved the battery to the back but I checked all my connections 100 times and used 0 gauge wire to try to fix it and it still did it. It didn't seem to have any other effect on my car other than it reseting the OD so I just ignored it. This is saying it's the gauge cluster itself? So I will have to replace the gauge cluster to correct this problem?

UltraZ,

As far as function I don't see the gauge replacement being a must. It will just reset the trip.....

It might not like the battery relocation but as long as it starts fine and you can live with the trip reset....I wouldn't bother. Mine works fine with a regular battery but it resets sometimes with the lightweight one. I've gotten used to it during "race season". After that the stocker goes back in.

I'm running a lightweight battery in the stock battery location as well. Maybe this is the source. The alternator did just go out, but I replaced it and I have the same problem. The car doesn't have any problems starting and it has been doing this for about a year.

I have seen this in my 99 camaro....usually when the battery is low.... chck all the ground wires again...

Yeah honestly it never really bothered me much. After instaling my th400 I haven't hooked up the speedo yet and the car starts fine so hell with it.

I have a '99 Z28 as well.

If I'm showing good voltage when the car is running could it still be my alternator or battery? There is no hesitation on startups at all and even when it resets there is no issue with idling(although its a little low at 500rpm)

You might want to double check that your battery terminals are tight.

Question on this, Would this mess up a tune????

Low voltage will cause this... but the early 99 pcm software had a fault that caused it to reset some of the memory values and act exactly as you describe. You can have the software updated at a dealer or find someone that can reflash the computer with a newer version.
Hope this helps,

Maggie

What lightweight battery are u guys using??

no... the trip meter is part of the gauge cluster, not stored in the PCM so this issue won't mess up a tune

Once a car is tuned, it's stored in the PCMs flash memory, so simply losing power won't cause it to be lost (the tune) ... even losing power momentarily isn't enough to clear the learned info in the PCM (such as fuel trims)

What new software is there? So I can tell my tuner. I am having this problem and mine is a 99. Thanks Art

Most dealerships usually charge $75 to $100 or so for an update.

Your tuner will probably have the latest stock version.

PM me if he doesn't.