'7747's and '6870's both use 2732 eproms.
I have previously successfully converted both of these types of ecm's to use more reliable 27c256 eproms and 28c64 eeproms.
Today I had big trouble with a '6870 ('85 TPI) that i had modifed in the same way to accept a 28c64/27cxxx etc...
If I wrote a .bin to a 28c64 it would start the car ok, but after about 5 secs of running, it would flash the CEL rapidly like it does when the prom is failed or missing. If I then removed the prom and verified it in the programmer, I found that about 20 bytes had changed! I have not had this problem before and haven't a clue why it is happening??? I went thru this process about 6 times.
The only way I could make it run was to use a UV eprom like a 27c256...

How is it that the contents of the eeproms was changing while in the ecm?????????

Ben.

 

Just happens from time to time. The older they get, that more exposure to static electricity, phase of the moon, and being the Holiday season are all contributing factors. The biggest common failure is when you just have one left.

Also, be sure not to be removing the PROM, until the ecm is done reading it. At shut off the ecm runs for a couple seconds to reset the IAC, unplugging the PROM while it's being read doesn't do it any good.

 

I had it happen a couple of times. Don't know if this was the fix but I set the buffer to "fill buffer" with FF. I was told this would "erase" or "reset" a eeprom.