Chevota

I have another thread going but thought I should ask this completely separately. If a have a prom out of a 1990 Chevrolet Tpi corvette that uses a 7727 ecm. Are there any other proms out there I could use in place of the damaged one I have now besides the original one? I honestly have no idea exactly what is in the cal pac part of the prom. And what is the board above the two calpac chips? Somehow I've managed to damage two proms. The eprom half of the prom checks ok. So I must have damaged the other half of the prom. Ahhhh! Thanks for any help. I'm coming up zero on another prom. I'm completely up the creek!

DZcode

From what I've read on the forums, the eight cylinder proms (within the speed density and MAF families respectively) are interchangeable with other eight cylinder proms. (I'm currently tuning with a used 305 camaro speed density prom in a '730 ECM and will switch over to a brand new in the box 350 covette prom later.) You should be able to use any eight cylinder prom within your MAS or MAF family.

Keep in mind that in "limp home mode", the closer the prom is to actual displacement the better. In my example, the engine displacement is 406 and the prom is meant for a 305. If the system goes into "limp home", the fuel management will be way off. That's why I'll switch to the 350 prom later.

There is also a thread about converting six cylinder proms to work on eight cylinder engines
https://www.thirdgen.org/forums/diy-...es-values.html

How do you know your current proms are damaged? Is there some test you've run or some symptom that indicates this to you?

Chevota

Are the proms damaged?

I have continually rechecked the eprom against the stock eprom I have saved as a file on my computer. I am using an adapter that lets you plug the whole thing into my pocket programmer II. I had used this same adapter to read, as I usually do, the OE eprom before starting the job. I have two complete proms that verify against this file too. So I'm pretty sure I've got that part right.

Where the problem exists is when I go to plug it into the ecm. I get no data on the aldl line, and it appears to be running in limp home mode. With the first eprom I had you could disconnect the battery, and then reconnect it. After you did that the ecm would work like normal for the first restart. After that it would go to never never land. Whatever I did to the second one, it never comes back from never, never land. I have tried another ecm just for kicks. Didn't help at all. Just complete loss on communication to the ecm when the problem exists. I can't even do an A-B and get a prom error code.

What kills me is this is by far not the first car I've ever chipped. And not the first with this type of Prom assembly. Although it is the first with the secondary board for what I understand to be ESC above the CALPAC. I've done earlier vettes in the past. And a lot of tbi.

Thanks,

Mab

Chevota

Another additional note - The second prom I got was working fine. The car ran fine. Everything was all good. I then went and plugged it into a chip adapter I got from moates.net. Nothing but sold check engine lamp. I plug the chip in by itself and it works. So I'm thinking there is something wrong with the adapter. I did do a test of the eprom code through the adapter, and it comes up valid. So now I'm thinking bypass the adapter. I snipped the eprom out and solidered in a dip socket. I have been unsuccessful getting that assembly to work since I did the solidering on it. Oh the pain! I don't see anything wrong with it. I tested the eprom with my adapter to plug into the programmer. So I was testing it as it was in the prom package. Comes up valid. So I must have done something to the other half of the board. I swear I was careful and have no idea how I did the damage. I'm thinking I had already done the damage when I had plugged it into the ecm via the adapter.
I can't find another prom oe part number. So I'm looking for alternatives. Not so worried about limp home mode. More worried about how it runs when the actual eprom is being used.

Thanks for listening to me.
Mab

Chevota

Thank you again for this info....DZcode. A long weekend made me take another look at everything. Well it seemed long. If I am understanding this right the two dip like chips under the knock board are just resistors for limp home mode? The resistance tells things like how many cyls., etc,.. Well I couldn't have damaged those with any ease at all.

So the question is if I damage the knock board what happens? I can't even get A-B jumper in ALDL to give me codes. I have two copies of the original eprom, now with all the pins on them cut. But before I had done that I verified each to an image file. They all check against it. Could I have an eprom that is not compatible with the ecm? I'm using an AM27C256-55DC. Could that be my problem? hmmm. I had bought a bunch of these I was using to chip honda/acuras.

RBob

iTrader: (1)

The AM27C256-55DC is correct for the $8D mask. It also matches the BIN size, so no stacking or offset burns required.

When using the moates G1 adapter the MEMCAL needs to be plugged into the side of it. The PROM goes into the socket. See the sticky's on the DFI & ECM board here for a post on what the MEMCAL, CALPAKS, and knock filter is.

The PROM is inserted with the notch facing toward the outside of the MEMCAL (or G1). If the G1 has a ZIF note that this is away from the handle.

Remove the MEMCAL and/or G1 from the ECM and look into the MEMCAL connector on the ECM. Make sure that none of the pins have been folded over.

Always look for the SES blink at key-on. This verifys that the ECM has successfully checksummed the PROM and is also running from the PROM. The blink is:

At key-on, engine-off: the SES turns on, blinks off, then turns on solid.

If no blink off, then the ECM isn't running from the PROM. If the engine is started the ECM will be in limp mode.

RBob.

Chevota

I've got no blink. Had it for a while when I got a new prom unit. But after I plugged it into the adapter board it went south. I can verify with the pocket programmer the eprom, and it comes back valid ever time.

Can I ask you. If I short a-b in this situation should I be expecting the computer to come back with a code for a bad prom? I was guessing I should get a code 51. I don't get anything. I believed I killed the first prom, and then three months later finally got a new one. It worked fine when plugged directly into the ecm by itself. Car ran, gave codes, gave data. I then plug the new one into the adapter board, with an exact copy of the eprom on my eprom plugged directly into the adapter board. Nothing but solid check engine lamp. I take it out and plug it back in by itself it works. So I'm thinking there must be something wrong with the adapter. I go a little crazy and cut the eprom off the prom and solider in a dip socket. Put my chip in. Plug it into the computer and solid check engine lamp! Now I can't find another of the original proms. I am doing something wrong. I just haven't been able to figure it out yet. I've done many other cars without a problem. I've done terrible things to the eproms, and never had a problem. I guess this is my payback.

I do have one more question. If you physically take the prom module out would you be able to get a code 51? Or the code to generate that code all lies within the eprom. There is no other base code in the ecm?
Is there an easy way to perform a checksum on my original eprom to verify that the copy I have that I'm using as my base is valid?

Marcello

Chevota

I think I got it! I just downloaded a checksum tester from the TunerCat website. And ran it on my bin file. OMG! the checksum comes up with an error. The file I've been basing everything on is in error? I can't hardly believe it. I have two copies of the chip and both verified against to the file a created using my pocket programmer. The calculated Checksum, and the stored do not match. I think I'm on to something. After truly understanding what was in the other half of the prom I see the problem really had to be the eprom half. How could I have effected some resistors? Doubtful. Hopefully, tomorrow I will see the light at the end of the tunnel.

Chevota

Now I'm really starting to scratch my head. I downloaded some bins from the Moates website to test with earlier on. I really wish I had had this program to test the checksums of bins before. I just tested the ones that I had downloaded. All the ones I was using are now coming up bad. The ones I never touched still look ok, accept one. ANHT 8D from seems to have come with a bad checksum right from the website. The funny thing is that was the closest to my OE prom. So that was the only one I had really tried to use. So everything I've done was based on bins with bad checksums! Oh the Pain!

JP86SS

iTrader: (1)

You can open the bins in TunerPro and view the checksum value.
Then click SAVE and recheck it to see if it changed.
Easy way to confirm if it is correct.