Advice on new PROM?

[88 Beater]

I've been trying to solve a problem with an '88 C3500. It had a burned up ECM which I've replaced but I used the old PROM. The truck still runs badly, just like it did with the old computer so I think it's running on the CALPAK and maybe I need a new PROM too. It's running noticably rich and rough but the SES light will not come on so I can't check for codes. Is this the way a bad PROM acts or am I running up the wrong tree?

Anyone got any advice on where to get a new PROM. Does the dealer even still have them? Rock Auto only seems to have the CALPAK. Auto Zone says they can special order a PROM for $69. I've also found custom chips for well over $100 but the truck is stock so I probably don't need anything like that. Anyway, just looking for good advice on where to go.

Thanks for the help.

[ChevyTech]

Be careful.

Terminology is all over the place and makes for poor communication.

Memcal, Calpak, PROM

You may be talking about the same part and calling it by a different name.

Oldest vehicles called it a PROM. Newer systems refer to Memcal & Calpak

I would test all power circuits and grounds to the ECM using a pinout chart.

[88 Beater]

I'm using the terminology out of the Haynes manual. My ECM has 2 removable chips and the manual calls the bigger one the PROM and the smaller one the CALPAK. Also, on Rock Auto, the pic of the CALPAK matches my smaller chip. The Haynes manual says the CALPAK is there to try to make the truck run if the computer fails in some way and can't run normally (and this seems to be the case). The pic I found on Auto Zone's website and the pic in the manual for the PROM matches my larger chip. Sorry if I'm using the wrong terms but I'm trying.

I've tried to check the pinouts on the connectors using the Haynes manual and the schematics in the FAQ. I haven't found any problems. Voltages seem to be good where they're supposed to be and grounds seem good too. I did replace the battery cables already since they were corroded and there was some resistance and voltage drop. New cables seem to have fixed that at least. I've also checked all the components that hook to the ECM and haven't found any problems but I have found some mistakes in both the Haynes manual and the schematic in the FAQ that had me chasing my tail for a while so I'm not 100% confident everything's actually right. If anyone could point me to a good pinout diagnostic chart / procedure, I'd appreciate it greatly. I did some searching but couldn't find one.

[ChevyTech]

Even GM service manuals have errors in them.


Take a look at these two links. They may be helpful.
http://www.chevythunder.com/1227747_ecm_198892.htm

http://www.wedgeparts.com/t8tbi-4.html

I have been hording parts for my TBI truck because I don’t want to end up not being able to find what I need as the years go by.

I have a lot of ECM & Prom charts. I will do a little digging and see if I can find out anything useful for you.

[ChevyTech]

1227747 ECMs use 2732 4Kbyte EPROMs

Here is another pin-out chart:
http://s-series.org/albums/DOUG-ECM-...ecm1.sized.jpg


PROM info links at this site for 1227747 ECMs
http://www.diy-efi.org/gmecm/ecm_info/1227747/

[ChevyTech]

When you had the ECM removed, did you ground the terminal for the check engine light to test the bulb and circuit and make sure the light works?

[88 Beater]

Originally Posted by ChevyTech

When you had the ECM removed, did you ground the terminal for the check engine light to test the bulb and circuit and make sure the light works?

Thanks for all the links ChevyTech. I'm going to read through all of them as I get some time today.

I did hook a 9v battery to pin A5 and A12 on the ECM harness and the SES light comes on just as it should so it seems like the computer just isn't able to turn it on. I think I understand what you're saying I should do - jump A5 and A12 with the truck battery connected? I don't remember having any voltage on A5 so if the ECM is switching ground on that circuit, I guess that could be an issue. I assumed the ECM was switching +.

I'll read through those links.

Thanks again and have a Merry Christmas.

[88 Beater]

OK - I jumped pin A5 to A12 (SES to ground) on the ECM harness with the key on and the SES light comes on. Those links were helpful but didn't reveal any problems.

I don't see what else this could be besides the ECM or PROM. The ECM is a reman Delco and when the first one didn't work I got it exchanged and the 2nd reman acts exactly the same. Any ideas besides trying a new PROM?

[ChevyTech]

You’re welcome, and Merry Christmas to you and everyone.

Grounding ECM terminal A5 with the key in the on position should make the check engine light come on. See this link.
http://www.wedgeparts.com/images/747ecm4.jpg

The link above is from this link I posted earlier:
http://www.wedgeparts.com/t8tbi-4.html

The test you did connecting a 9v battery to the circuit could make a light come that would otherwise never light if the truck has a problem that causes it to not supply power to this circuit.

Edit:

You replied as I was typing my message.
That is a valid test and I agree if all other ground and power supplies test good there must be a problem within the ECM.

If you hadn't replaced any parts my first guess would have been a bad ECM.
On this stuff you are never sure until it is fixed.

[ChevyTech]

I just went and looked in a GM service manual.

The manual states the PROM or ECM could be at fault.

It states you should replace the PROM only after replacing the ECM first because a PROM (CAL-PAK) is an unlikely cause on this problem.

[88 Beater]

Thanks for the help again ChevyTech. I guess I'll get a new PROM ordered and see if that does it. My original ECM was visibly burned up so I guess maybe it took the PROM out with it.

[ChevyTech]

You’re welcome!

Let us know if the new PROM fixes it.

[88 Beater]

Ordered a new PROM from AutoZone on the 26th. Just got e-mail that it shipped today. Hopefully I'll get it early next week.

[88 Beater]

Well after waiting almost 2 weeks, I finally got the new PROM from AutoZone. It's the wrong kind of chip. I think it's one for a newer GM computer but not totally sure. I guess I'll send that back and look for another source. If anyone has any suggestions for a good place to get one, please let me know. Right now, I'm not seeing any options besides a custom chip maker.

[ChevyTech]

Every time I hear of someone have trouble finding parts, it makes me want to hoard more parts for my TBI truck.

I get most of my “inventory” from the local U-Pull-It.

[88 Beater]

After a little searching and calling around, I decided to order one from www.tbichips.com . I exchanged several e-mails with Brian there and he was incredibly responsive, usually e-mailing back within minutes. He even wanted to verify what troubleshooting I'd done to make sure I actually needed a new PROM. His recommendation was to replace both the PROM and CAL-PAK so I ordered both. Prices were reasonable - $80 for both chips. He said he'd get them shipped today so I should get them by the end of the week I think. I'll let you all know if that fixes it then.

[88 Beater]

I think I've finally fixed the problem. It wasn't the PROM. Turns out the problem was several bad ECMs. I got the new PROM and CALPAK but still no SES light with 2 Delco reman ECMs from Rock Auto. Finally tried another reman Cardone ECM from AutoZone and it seems to work correctly with the old PROM and CALPAK in it. I still need to take it for a good drive and check for codes but at least this ECM can turn on the SES light. Also, the truck starts up after about 1 second or less of cranking instead of about 5 seconds it took with the bad computers.

Obviously, every situation can be different but here's what I've learned.

1. ChevyTech was right. The problem is more likely to be an ECM than the PROM/CALPAK. I had to go through 3 reman ECMs to get one that would even turn on when you put power to it.

2. The packaging and instructions with the Cardone brand ECM were exactly the same as the Delco. The only difference seemed to be the brand label so I'd save the $20 or $30 because they seem to be the same thing.

3. I hate trying to diagnose black boxes. Actually, I already knew I hated that but there was a lot of hair-pulling on my part to try to make sure the truck wasn't frying ECMs as soon as I plugged them in and that the connections were all actually good all the way into the box. Having to go through so many "100% tested" parts to find a good one makes me wonder how they test them. It must not be a very comprehensive process. I wonder if they're just replacing obviously burned up parts, checking a few voltages and calling it good.

[ChevyTech]

Thank you for taking the time to post an update. The feedback is helpful.

In the dealership, (my employer), Delco remanufactured parts were very problematic to the point the techs did not want to install any of their remanufactured engines because of the very high failure rate.

My opinion is that the remanufactured parts have a huge quality control problem.

I agree that the tests are probably very limited, and possibly some parts are not tested at all.

Also, how many people try the ECMs, and returned them, and they just sell them to the next person, instead of sending them back.

[88 Beater]

Originally Posted by ChevyTech

Also, how many people try the ECMs, and returned them, and they just sell them to the next person, instead of sending them back.

That's a good point. It was part of the reason I tried a different retailer for the 3rd one. Hopefully I can get a refund out of the place that sent me the 2 bad ones.

[88 Beater]

Now that the ECM's working, I've been able to move on to other problems. This morning I found another thing for my list of "Holy Crap, how did this thing run?"

The truck was still idling too fast and running rough so I thought I'd throw some new plugs, wires, cap & rotor on it and check the timing. I'm glad I double checked to see if the old wires were on in the right order. They weren't. It wasn't just one or two in the wrong place either. They were all in the wrong places - every single one - not even in the correct firing order. The timing was way off too. Maybe it had to be to make it run like that? Anyway, it idles like a new truck now and drives pretty nice for a beat up old POS. Still a few more little problems to fix but finally feels like I've turned a corner on it.

[Mr_Rich]

One of the problems with electronic parts like this is that you have to be very careful about static discharge. That will ruin circuit boards. Some circuit boards are much more vulnerable to static discharge than others. Treat them all the same. I think proper handling of electronic parts like this are largely ignored. I make sure that I'm grounded or wearing a ground strap if I'm handling parts like this, and definitely if I'm swapping chips.

[88 Beater]

Originally Posted by Mr_Rich

One of the problems with electronic parts like this is that you have to be very careful about static discharge. That will ruin circuit boards. Some circuit boards are much more vulnerable to static discharge than others. Treat them all the same. I think proper handling of electronic parts like this are largely ignored. I make sure that I'm grounded or wearing a ground strap if I'm handling parts like this, and definitely if I'm swapping chips.

True enough about the possibility of damaging an IC with static discharge. I work with electronic components quite a bit and I was grounded. Good advice.

[Motorhead420]

Originally Posted by ChevyTech

Be careful.

Terminology is all over the place and makes for poor communication.

Memcal, Calpak, PROM

You may be talking about the same part and calling it by a different name.

Oldest vehicles called it a PROM. Newer systems refer to Memcal & Calpak

I would test all power circuits and grounds to the ECM using a pinout chart.

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