factory pcm or not? I need help

**98GTPPACE** · 05-25-2013

Hey Everyone. I am looking for a little input. I just picked up a 1998 Pontiac Grand Prix GTP. I am trying to figure out if it has an aftermarket computer installed. IS there any way to tell? Car has a zzp 3 inch downpipe U pipe delete and a cold air intake. Any help will be greatly appreciated, Thanks guys.

**coolone** · 05-26-2013

If the fans stay on when you shut the engine off then it's been tuned!

**Iceman6669** · 05-26-2013

My car has been tuned and the fans do not stay on..

**coolone** · 05-26-2013

Originally Posted by Iceman6669

My car has been tuned and the fans do not stay on..

Ooooops, ok, I stand corrected. MOSTLY, but not all tunes will leave fans running a minute or two after ignition shut off for cool down. It may or may not be an indication that there's been a reprogramming of your PCM. You can also try and pay attention as car heats up and temps and see when fans turn on. Stock turn on temps are usually higher. Otherwise the only real way to know is to READ the settings from the PCM itself and see if it is not stock.

**98GTPPACE** · 05-26-2013

Awesome Thanks for the help! Yeah the fans stay on for a minute or two when I shut it down I will check later on and see what temp they come on at though.

**Frosty** · 05-26-2013

Theres a few key signs.... one is being able to drop into 1st above 34-35 mph. Another would be fans coming on at any point below 200 degrees while running (I dont remember stock temps and i have hptuners on my other laptop). Also while our pcms all have the ability to run the fans for a bit after shutting the car down none of our cars came with it enabled so if the fans run at all after shutting the key off you know you have a tuned pcm of sorts as well. There is also the typical removal of the speed limited but unless your in mexico be careful about testing that. You could also try pulling the egr plug off of the egr and see if it throws a check engine light. Most tuned pcms remove all of the emissions checks.

Only way to really really know whats going on is to have someone dump your pcm into a laptop and check it.

**Iceman6669** · 05-26-2013

Let the car get to 110* and whack the oil pan n see if you get any KR.

**txslow6** · 05-26-2013

If you think it might be a shelf tune, then look at the PCM. Every vendor puts a sticker on the PCM with their name on it. Most owners don't pull the sticker off or if they do there is still residue left on the PCM.

**Frosty** · 05-26-2013

My pcm is far from stock and has never been out of the vehical.... No stickers. Also a tuned and stock pcm should both read kr.

**Explicit_Spade** · 05-26-2013

Originally Posted by frosty

My pcm is far from stock and has never been out of the vehical.... No stickers. Also a tuned and stock pcm should both read kr.

So its not a "shelf tune" and what txslow6 said doesn't apply...

If the previous owner was swinging from the short d of ZZP like it sounds like they were, odds are it probably has a zzp pcm.

**Iceman6669** · 05-27-2013

Originally Posted by frosty

My pcm is far from stock and has never been out of the vehical.... No stickers. Also a tuned and stock pcm should both read kr.

I realize both tunes will read KR. That's why I said 110*. Stock tune doesn't turn on the knock sensors till 160* and most tunes turn them on at 100*.