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Old 07-14-2012, 04:36 PM
Join Date: Jul 2012
Posts: 1
Default 1988 GMC 1500 computer

Hi, I'm new here so if this has been addressed before, I apologize.

Recently my truck began acting strange, flooding out, engine speed running up and down when it was sitting parked and running, the engine would die when you tried to give it gas, etc. I went by an auto parts store and had them check it with their tester, and it was throwing all sorts of codes saying everything was bad, even things the truck doesn't have, like a turbo charger. My cousin is a mechanic and he was there looking at the readout, they both agreed that what I need is a new computer.

Went in to look the part up, they have the computer, but it requires me to take the PROM (?) out of the old one and put in the new one. Both agreed that I should get a new PROM, and that I'd have to get that from a Chevy dealer. No problem there either - but I wanted to get the opinions of you gentlemen who know a lot more than we do first. So here's my question:

Is there a computer/PROM setup that's a performance improvement over the OEM one that I should consider? If so, where could I get it. Or should I just stick with the stock one?

My truck is a 1988 GMC Sierra 1500 4X4 standard duty long bed 350 automatic throttle body.

All advice and help will be greatly appreciated.
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Old 07-14-2012, 06:45 PM
NullHead's Avatar
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Join Date: Apr 2011
Location: Detroit, MI
Posts: 1,063

I personally don't know much about this subject, but I do know where to get you a chip.

I'd call up the guy here: TBI CHIPS Tell him your situation and what kind of truck you have and all that, and I'm sure he can hook you up. I have never used his products before, but I have heard good things (Mainly from thirdgen.org). He can probably delete your EGR, change fuel trims for you. I'm thinking one of his chips can improve performance.

The prom lives under a little cover on the ECM itself. So no big deal to swap the prom.
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Old 07-15-2012, 11:07 PM
Junior Member
Join Date: Nov 2011
Location: Mukilteo, WA
Posts: 74
Default It might not be the computer...

The uneven idle, wierd codes and performance issues could be a bad intake manifold gasket...mine was sucked in between 2 & 4 just enough to cause problems. Once I changed that it ran like a whole new engine. Cost: $12 for a good set of thick gaskets and $5 for Permtex type 1 ('a' or 'b', that just refers to the tube size). I don't use silicone sealers in my engine, but what you use is up to you. if your intake manifold isn't perfect, nothing else will work right. That goes for the seal between your TBI unit and the manifold. Have you put a vacum guage on it yet?

While ya got it off....it's an '88? Is it now pollution-check exempt? Mine is now, at 25 years.
I didn't take the smog pump off for now, as I needed the roller for the belt. However, I gutted it and now it is just a spool. I took off all of the associated hardware, plugging off the nipple in the TBI. I took the tubes off the exhaust manifolds, cut them down and flat-rolled them like a toothpaste tube. I took off the EGR and cut out a metal patch to seal off the manifold. I removed the cat and replaced it with a straight 3 inch pipe to the single 3 inch Flowmaster exhast. I set the ignition at 6 degrees, but be sure to disconnect the knock detector first or you will have headaches.

The truck runs so much better now that you just wouldn't believe it. Total cost is the gasket, Permatex, and less than $50 for the exhaust. tubing.
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Last edited by Mukilteo; 07-15-2012 at 11:13 PM.
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Old 07-15-2012, 11:07 PM

1500, 1988, 88, aftermarket, body, chevy, computer, forum, gmc, parts, pollution, problems, remove, shold, sierra, silverado, throttle, truck

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