Corrupting chip?

[ralmo94]

So my 1994 GMC k1500 5.7 4l60e with 6395 ECU, running $0D, has had an issue where the chip seems to get corrupted. It's a genuine SST I bought from Moats in 2020, soldered to a memcal. Seems out of no where it will all the sudden go into limp mode, place stock memcal in and it runs on it, check the chip with the file burned to it, and it does not match, so I assume the only thing that would do that could be the alternator? It has a parts store one on it, it charges, but what else could cause this?

It's not used much right now, but I'd like to be able to take it on road trips more reliabily. I have two possibilities for doing that, 1 parts cannon, or replacing the alternator, or 2 soldering a chip in a spare memcal so when it happens I can swap memcals and be on my way. It's done this a few times, but it seems to take a while, it's not an immediate deal. And once I burn the chip it's fine again. When it happened before I thought Maybe it was something to do with the chip adapter, but I have that eliminated now with the chip soldered to the memcal, and it has still done it twice since. It doesn't get a lot of miles on it, mostly a spare truck, but my brother might want to take it out of town for work, and I'd like it to be reliable.

So any ideas, or anyone have anything like this happen before? I haven't read anything like this before.

Also I don't think it's related, but on occasion it will stall while idling, restarts fine, but won't restart unless you key off then back on. Always seems to do it that after it's warmed up. Logs just seem to show it quits running, kinda hard to diagnose, as its intermittent. Ignition switch has been changed a couple years ago .
Truck has fresh tune up cap rotor wires plugs oil change ,new fuel tank pump and lines in 2020, and rebuild the TBI then too. That's all I can think of thanks.

[kur4o]

You can get one time burn chip [eproms]. If it doesn`t keep state the chip is for the trash.

[MO LS Noobie]

It does sound like the chip or even something in the PCM itself. Do you have a complete spare computer you could swap in? I did not have any experience with the OBD 1 reprogrammable chips chips, any reprogramming I do is on the GM OBD 2 stuff.

To test the alternator, put your voltmeter on AC, one lead on the negative post of the battery not the clamp but directly on the post, and the other lead on the output of the alternator. Anything over 0.2 V is too much. You can see it more clearly with a lab scope but a voltmeter works fine. I haven't seen temperature affect it very much but you can check it hot and cold. You might also check the actual output, should not be over 14.6 V. And is always triple check your grounds.

I never had a PCM intermittently lose its memory, but have had several go "stupid" and require a key off and then restart sequence. Internal computer, stray EMF from computer and sensor wires being too close to faulty spark plug wires, and AC ripple voltage from alternators.

[dave w]

So any ideas, or anyone have anything like this happen before? I haven't read anything like this before.

After about 1 year of working perfectly, the ZIF socket (low profile) that was installed on a G1 Memcal adapter board cause many of problems your experiencing. I removed the ZIF socket and installed the chip directly into the G1 Memcal adapter board. Some 6 years later, with the chip installed directly into the G1 Memcal adapter board the chip is still working flawlessly.

[ralmo94]

If it doesn`t keep state the chip is for the trash.

I was afraid of that, I do have another brand new chip I could solder to another memcal.

It does sound like the chip or even something in the PCM itself. Do you have a complete spare computer you could swap in?

Yes and I have swapped it but it doesn't seem to do anything different.

To test the alternator, put your voltmeter on AC, one lead on the negative post of the battery not the clamp but directly on the post, and the other lead on the output of the alternator. Anything over 0.2 V is too much. You can see it more clearly with a lab scope but a voltmeter works fine. I haven't seen temperature affect it very much but you can check it hot and cold. You might also check the actual output, should not be over 14.6 V. And is always triple check your grounds.

I'll have to check it with a multi meter.

After about 1 year of working perfectly, the ZIF socket (low profile) that was installed on a G1 Memcal adapter board cause many of problems your experiencing. I removed the ZIF socket and installed the chip directly into the G1 Memcal adapter board. Some 6 years later, with the chip installed directly into the G1 Memcal adapter board the chip is still working flawlessly.

Did you have to re burn the chip?

I have taken the adapter all the way out of the equation, but maybe it was too late for the chip?

[dave w]

Did you have to re burn the chip?

No. Removed the ZIF and installed the chip directly into the adapter board.

[ralmo94]

So interesting update, haven't had time to mess with the truck yet, but it was in the way so I had to move it, first time it was still in limp mode, second time it ran fine. So I still need to verify the chip with the bin to see if it still matches or not, but last time it did this it didn't match.
Still have to check for AC ripple voltage.

[ralmo94]

Another update.
Checked with multimeter, and get 0 v ac while engine running, DC is about 14.4v. Also truck has started and ran fine without doing anything to the chip. It also passed my attention previously, but the neg terminal is coroded.

[MO LS Noobie]

I never saw a perfect diode pack in an alternator. Lowest ac voltage that I have seen with running engine is 0.005, most are closer to 0.010 VAC. The dirty battery terminal would definately be an issue.