Looking for some insight here. I have never had a this problem before and it has thrown me for a loop. I'm working on a 1990 Chevrolet Corvette with a 1227727 ecm. I pulled out the OE prom, and put an adapter from Moates.net in to allow for me to put a eprom in place of the OE eprom. Car started up fine, and drove fine. Come back to the shop, turn it off. Go back to start doing some mods to the chip. I put an exact copy of the OE chip in my eprom at first to make sure all was good with hardware before I started doing anything with software. Go to restart it, and solid check engine lamp. Hook up the a scanner, and no data on the line. Check power and grounds. All check ok. I have 5 volts at the 5 VDC ref line. I unplug the ecm, and pull my chip. Put the OE back in alone. Start it up. Checks ok. No check engine lamp. Runs good. Turn it off, and presto back on solid. Again no data on the line. And yes, I had data when the check engine lamp was out. It seems that once the computer powers down, it just won't power up right again. I got a reman. ecm, and tried that. No luck, same exact thing. If I unplug the computer, and start it up again. It will work until it is shut down. After that it goes back to no data. Unplug it, and again it works. I can't even get a code 51 when I jumper A to B in the ALDL. Has anyone ever had something like this happen? I'm wondering if I damaged the Calpack portion of the PROM? And if this is the bad part, can a prom be bought without the eprom? Just the part I need? So far I've found one source for a new prom at $171 my cost. Ouch! If you pull the prom, and attempt to power the ecm - would you get a code 51? Or do you need the calpack for that to happen? Really looking for some insight. Thanks, Marcello

If you did not set the correct offset for your chip you will have problems. Goto http://www.moates.net/documentation....entation_id=75 to check your offsets.

Also, don't forget to disable the checksum before you start making changes to the bin, otherwise you'll have the same problem. (do so by placing 0xAA in the mask ID byte)

I would think if that were the case it would happen the moment I start the car. Wouldn't I have a check engine lamp immediately? I don't I have live data the first time I start the car. And no codes stored. I would think I would have a code 51 - prom error or something.... Nothing. Then on next start up....no communication whatsoever. Weird?

Now saying that I've never removed the checksum routine on a GM ecm before. Everything I've done included recalculating the checksum, and making that part of the chip. Is it easy to find the checksum routine?

I finally got it running. I bought a new prom/memcal complete. It worked! I then tried to use an adapter to allow for a modified chip. No dice. I then got really crazy and cut the 27c256 off the prom/memcal pack. Installed a 28pin dip socket. And put exact copy of the OE chip in the socket. Dead again! This time it doesn't even work on the first restart. OMG! I've never had so much trouble as this car. I hope I can find another prom/memcal pack. It cost me $160 for the first one, and it took me 3 months to find it. There must be something I'm missing with this car. 1990 chevrolet corvette vin "8". ecm 127727. Why can't I change the chip? Is there something odd with the prom/memcal pack on these cars?

I'm having a similar problem on an all stock TA. At the moment i'm waiting for a new ecm and calpak. I'll let you know what I find if you haven't found out by then.

I think my coil took out my ECM. Both appear to be bad. Maybe it's just a coincidence though.

Yes, It might be a while before I get a new prom. So far I'm coming up blank. Still looking for another one. I'm looking for a GM PN#16134293. Anyone happen to come across one of these, or something I could use as a replacement for the calpac half of the prom. Thanks, Mab

I have the same ecm, hope I don't
have the same problems