92 Firebird...A serious problem? ECM/PROM

The PROM means "programmable read only memory." It's a chip that's in your ECM that gives the ECM the program to run your engine. You can get a new one at the dealer. I think it'd be less than $100. Make sure you bring your VIN number so they can give you the right prom. I'd check the codes one more time and make yourself more certain that that's the code. It's relatively easy to change, you need to remove the kick panel above the passenger's feet and the ECM will be up there. It's an aluminum box about

1.5"x6"x4". On the ECM will be two hex screws that hold a plate, the Prom is underneath that.

-Bruce

Think of the PROM (Program Read Only Memory) as the "software" that the vehicle needs to run. It's the "instructions" that make the silver box (the ECM) do its thing.

In turn, that silver "box" can also be used on other vehicles, but the PROM is the specific set of instructions programmed for only a few vehicles.

A PROM should run you about $55 or so through any GM dealer. I would bet that GM updated that PROM a few times since '92, so it certainly wouldn't hurt to upgrade.

You can usually bring the PROM with you and the vehicle information and the dealer should be able to order the right one. The letter/number suffix codes and the part #s on the unit usually appear in the Service Parts catalogs and can easily be crossed over/superseded up to the current part for the application.

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Beautiful...Why can't Haynes be as simple and yet provide the info you need like that? Does my problem sound like something that would/could be a PROM. THe simple fact that it appears to be something that is controlling EVERYTHING with some sort of relay(a/c, fan, injectors, etc) has me believing that it could be. Quite frustrating indeed!!

The prom or the ecm could be at fault, but either way start with the prom. I bought an updated prom once and it ran just the same. What do you think they update on it? All aboard the Yankee express, next stop October.....

Fuel trim, timing, correct emission and performance problems, part is from a different vendor than the original, etc, etc, etc, etc, etc, etc, etc, etc, etc, etc, etc.

GM service bulletins usually key you into why the change is being made. Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

You can take your ECM to any parts store and their electronics supplier can have it tested for you. That would rule out a bad computer (ECM) for starters.

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

make sure to disconnect the battery before messing with the ecm

PROM = (P)rogramable (R)ead (O)nly (M)emory. It is the software (firmware actually) in the chip(s). Basically, it means probably that there is a catastrophic failure to access or make sense of the computer code stored on the chip(s) in your module(s) or that a chip fails a checksum value. You may have an "insane" module (like the ECM perhaps). Bear in mind I am a computer tech with a light to moderate (that's probably being kind to myself) grasp of the technical workings of modern cars.

It might be the place to start looking at. Don't know how you "test" a module without swapping it out for a known good one though. Probably the others here will offer better advice.

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That sounds really intriguing but... it seems almost too good to be true that general purpose parts stores could test so many specific type of ECMs and PROMS out there. Plus I read in this forum a lot that at least for ignition modules, some of these parts store tests are to be kind shall we say, less than reliable. Is it okay to test them at the parts store or is something else needed in order to get reliable results?

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Can you dump the code, hack it, and reflash it? Would be interesting to see what sort of innerds it's got...

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The answer is maybe. There are 3 basic issues:

1. Of course you would need to have the proper equipment to read the PROMs and then maybe program some other PROM, EPROM or EEPROM which could be substituted.

1. If the PROMs used in the cars are somehow encrypted, this would have to somehow be defeated or otherwise re accomplished in the new chip.

2. Assuming obstacles 1 and 2 are overcome, a person would need to know what code to put where. Some of the code might be object code (actually executed by a processor) or it might be data. In this domain, you pretty much would be limited to modifying simple data values. Wanting to change the object code would likely require a herculean effort to reverse engineer the original, or gain access to the programmer's source code which it was assembled from in the 1st place.

Essentially, without published >Can you dump the code, hack it, and reflash it?

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Part of the problem with places like Auto-Zone testing stuff is the people. The people who are smart enough to do it properly are rare. Out of those very few are even shown how to opperate the equpiment properly.

The other part of the problem is the equpiment. Not allof it works as it is supposed to, and at times the charts and manuials are wrong for specific applications.

Maybe Joe has some better input on this. Charles

Again...

The parts store will send it out to their ELECTRONICS SUPPLIER for testing :).

They can and do have the equipment to test computers and other electronic components :). Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Again, the parts are sent by the store TO their electronics supplier/rebuilder for testing.

They have the proper equipment to determine if the ECM is indeed bad internally or not. Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Well....I pulled a used ECM from the junkyard for $50 and it worked like a champ. Problem soved! Thanks for all the input.