Does anyone know if there is still a source for PROMS. Don't know if mine is good or bad but I'd like to have a backup plan. Is there anyway to tell if your PROM is good or bad or is it usually the computer board that goes bad?
Source for PROMS
- Thread starter justacruzr2
- Start date
Only sources are used or NOS. They do not make the type of PROM chips our ECMs use. If you have a Chevy style CCC system there is a member here called bitflipper who burns clones of ZZ4 PROM chips but they require installing an 87 or 88 ECM.
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dont know if ecm bad? ok here's how ya tell... it;ll run & drive but it will run as if you pushin a full dumpster on foot. nothin registers on the anyalisis plug in for code.... i had to drive 2 miles or so to get to a dealer and expect something bout like this for the ride....
not sure this wil help but......
not sure this wil help but......
Do you have a chassis service manual for your car? It goes through entire test procedures to determine if your computer or your prom or your sensors are at fault. OBD1 is the simplest computer system out there for our cars. 99% of supposed ECM problems are bad or misadjusted sensors/wiring, not the box itself. Do ECMs go bad? Yes, but rarely. It's unfortunate though, that there's no aftermarket support for PROMs.
In many instances, you should get a check engine light when the ECM acts up. This is not guaranteed as previous "genius" owners may have removed the CEL bulb, or disabled the lamp somehow. When that happens, it's simply moronic, IMO. You either need to keep your ECM system in tip top condition or it does no good, might as well rip it all out than let it languish. Also, depending on the fault, it could send the system into "Limp Home" mode where your timing is locked and you can drive it, but it's very much compromised. No timing advance or anything, and you know there's something needing attention.
PROMs are normally NEVER a problem, unless you start swapping them, and electrostatically zap them because you're messing around where you may not have to and accidently ruin them. Not saying they won't ever fail, but I've never had a PROM failure ever. And I don't know of anyone who has. I'm not blind to the fact that it's another part, thus another fail point, so I'm sure someone has had one or more fail, but they're pretty robust, generally.
The issue with PROMs is that GM coded them for different years even if they had the same exact programming (84 H/O and 85 442 are exactly the same PROM, although federal mandates say they must have different codes, thus different part numbers). We know this because the carb, distributor, sensors, engine and driveline components are exactly the same with date codes the only real difference.
86-up used a different ECM box altogether than the 85 and older due to differences in things it controlled and the way it controlled. So you have to watch out for that as well. I know this to be true for Oldsmobiles, maybe not others, I don't know. Mixing and matching without knowing what you're doing COULD give you a mistaken ECM or PROM failure which is likely in the previous example of a GP 86 ECM in an 85. Might be the same, may not be. I don't know.
99% of the time, you can swap in a similar year, similar engine, complete ECM with its prom from another car if your ECM is in disrepair. Like an 84 305 4bbl wagon should be similar to your car and would likely work fine. Or steal the PROM out of it if your PROM is verified to be bad. I would go that route unless you're building that ZZ4 specs. No real need for that if you're going to run stock. Keep in minde the systems were made for economy and emissions considerations. The biggest issue is that we DON'T know what exact calibrations are inside of each PROM.
They have rebuild ECM boxes for your GP at places like RockAuto should you need one, you would just need to swap in your PROM if it's still good.
But first- do the checks to ensure you rule out the ECM and/or PROM before you go shooting a parts cannon at it.
In many instances, you should get a check engine light when the ECM acts up. This is not guaranteed as previous "genius" owners may have removed the CEL bulb, or disabled the lamp somehow. When that happens, it's simply moronic, IMO. You either need to keep your ECM system in tip top condition or it does no good, might as well rip it all out than let it languish. Also, depending on the fault, it could send the system into "Limp Home" mode where your timing is locked and you can drive it, but it's very much compromised. No timing advance or anything, and you know there's something needing attention.
PROMs are normally NEVER a problem, unless you start swapping them, and electrostatically zap them because you're messing around where you may not have to and accidently ruin them. Not saying they won't ever fail, but I've never had a PROM failure ever. And I don't know of anyone who has. I'm not blind to the fact that it's another part, thus another fail point, so I'm sure someone has had one or more fail, but they're pretty robust, generally.
The issue with PROMs is that GM coded them for different years even if they had the same exact programming (84 H/O and 85 442 are exactly the same PROM, although federal mandates say they must have different codes, thus different part numbers). We know this because the carb, distributor, sensors, engine and driveline components are exactly the same with date codes the only real difference.
86-up used a different ECM box altogether than the 85 and older due to differences in things it controlled and the way it controlled. So you have to watch out for that as well. I know this to be true for Oldsmobiles, maybe not others, I don't know. Mixing and matching without knowing what you're doing COULD give you a mistaken ECM or PROM failure which is likely in the previous example of a GP 86 ECM in an 85. Might be the same, may not be. I don't know.
99% of the time, you can swap in a similar year, similar engine, complete ECM with its prom from another car if your ECM is in disrepair. Like an 84 305 4bbl wagon should be similar to your car and would likely work fine. Or steal the PROM out of it if your PROM is verified to be bad. I would go that route unless you're building that ZZ4 specs. No real need for that if you're going to run stock. Keep in minde the systems were made for economy and emissions considerations. The biggest issue is that we DON'T know what exact calibrations are inside of each PROM.
They have rebuild ECM boxes for your GP at places like RockAuto should you need one, you would just need to swap in your PROM if it's still good.
But first- do the checks to ensure you rule out the ECM and/or PROM before you go shooting a parts cannon at it.
Which would require using the engine compartment and probably the instrument panel wiring as well. That was one of the things I had to do when I removed the 231 v6 and installed the 305 sbc. Sensors were different on the '86 than the '84.
I am currently in limp mode. carb and distributor are unregulated in that mode. Cold start is where it's most noticeable. With the choke plate closed and the MC solenoid not being used it's just dumping fuel in the carb. After about a minute it's OK but still sucking more gas. than usual.
When I did this restoration I used the ECM from an '83 GP that had the 305. It worked perfectly fine in my '84 with 305. What I have noticed is it seems that different years use different ECM's. I'm sure they were always updating them to make them more efficient. The '83 ECM is a 1226025. The '84 is a 1226455 and the '86 is a 1226519. For each year the only difference is the PROM chip based on the model vehicle and engine and probably trans and rear end ratio. As I replied above, you may also have to bring over the wiring from that vehicle on a mix and match. I also saw that RockAuto has the ECM available @$247.00 from BSE. Cardone was $99.00 but I don't trust Cardone and you get what you pay for. However, if the PROM is bad a new computer won't help.
84 Grand Prix with 305. The computer service number is 1226455 and the PROM code is BDX. Though as I said above, the 83 Grand Prix computer, 1226025 with a BKF PROM worked perfectly fine in my car as well.
I swapped the 231 out of my Regal for a HO 305 and 2004r. Had to swap the engine computer harness but was able to keep the original instrument harness. Later I changed the 86 ECM to a 87 ECM without issue, it works fine with the 86 harness. The zz4 prom makes a difference.
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