So I was looking up parts on O'reillys website and I found something pecuilar. I was bored so I looked up part interchange for the computer. They have the 2.5 tbi, 2.3 Mpi Dohc, 2.0 Sohc, and 4.3 tbi all listed as interchangeable with the computer. That can't be right, they would all need different programming except for maybe the 2.5 right? Just found it interesting. I know on our racecar last year we had the 2.3 DoHC engine and it had the SOHC computer in it and it ran like that. Changed to the correct computer and didn't seem to make a huge difference. Do the older computers have multiple programs on them?

The computer itself doesn't have any programming. The PROM has it all. The actual computer might be the same for all those engines, but the PROM is different.
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But isn't the prom inside the computer. So they wouldn't really be interchangeable unless you switched the proms right?

Right.
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and now from the guy who doesn't know much of anything...

Would it really matter to get the CORRECT PROM?

My thinking is this:

PROM is PROGRAMMABLE Read Only Memory, meaning that it is programmed but unchangeable? Sounds like it would be set at the factory and you would in-fact need the correct PROM in any silver box, but...On my old Skyhawk, the computer took a crap on me (ewww...) and being a geek, I looked into replacing it myself before I thought (yeah, right) and took it to the garage.

If my crazy-photographic-remember-everything-useless-but-nothing-important memory serves me well, I thought there was something I read (about 20+ years ago) about when installing the new computer, the PROM would have to be set (or maybe reset). If that little tidbit is correct, then wouldn't it be possible to use any ECM (as long as it is for a J, since it wouldn't know what to do when installed in a Honda) and when the part of the process for setting/resetting the PROM comes, it would set itself to the car it happens to be installed in?

Hope my thoughts there make sense, and I'm sure you'll set me straight...

No. The PROM has absolutely no idea what car it's installed in or what engine it's trying to run.

It is possible to replace the PROM with an EEPROM which can erased and reprogrammed. The ECM will interchange between specific years of specific cars because the harness connectors are all the same, but the program used to run those drivetrains is different.

If it's the same drivetrain in a different car, then the PROM does not need to be replaced/reprogrammed.


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Mike

Just to make sure I've got this...

If you are replacing the ECM on a 2.0 Sunbird, you can't take an ECM from a 3.1 Sunbird, put it in the car and reset the PROM that is in the ECM from the 3.1? You would still need to use the PROM from the 2.0's ECM?

You can't reprogram PROMs at all. You can only reprogram EEPROMs. Although I've never done it, if its the standard GM socket shape, you can physically put the 2.0 PROM in the 3.1 ECM, but thats it. No reprogramming (resetting as you're calling it) at all. But, no, you can't just put a 3.1 ECM with a 2.0 and expect it to "reset" itself. The PROM is a chip that doesn't change. I don't even know if the 3.1 ECM will run the 2.0 ignition, even if you put the 2.0 PROM in there to do it.......

PROM- chip with specific program (not changeable) for specific engine
EEPROM- chip with base program (changeable) with variables changed to match specific engine (fuel maps, EGR function, etc)
ECM- circuit board to provide complete circuits for the PROM/EEPROM to operate through for specific engine(s)

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And I've just read what I wrote, and I'm tired, so i don't even know if it makes sense.
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I think the V6 ECMs are physically different from the L4 ECMs anyway. I remember when I did my swap, they looked different.

Pretty much, if the ECM fits and hooks up to the harness, and you have a PROM for the engine the ECM is hooked up to, pop in the PROM and you're good to go.


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Mike

James--

if it makes sense to you or not, you made it make sense to me!

Mike--and that answers the original question of the thread perfectly.

are u able to buy aftermarket EEproms for more perforance?

yup jetchip.com sells them i had a 94 2.2 with one in it worked great used to work there too lol

michael, i am looking for a chip on jetchip for a 94 cav 2.2 but all i can find is a listing for the 3.1?

I believe only the 3.1 will see any gains from a new chip, Ive never heard of getting a new chip burned for a 2.2

I'm almost 100% sure there was never a Jetchip for the 2.2. I would have seen it before, or at least heard of it by now.
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ya, i;ve never seen anything either.. but micheal koldus apprently use to have one in his,, and he worked there? so i donno

i'd pm micheal but apprently he hasn;t been on since 2004 anyone else have any ideas?

His last update was from 2004, but he just posted in January. If you want to make power with the 2.2, you'll need more than a chip, and would see alot more gains with other mods.