I just got a brand new memcal from the chevy house the other day and I opened up the top and it is a "AUJP 1615 1348" problem is, it has no UV window on it and if I read it as a 27C256 then it opens fine as $8D in Tunercat. If I read it as a 27C512 then the file won't open in TC as it says it is the wrong file. The chip says "M27C512-12B3" It is an ST chip. Haven't seen this one before. I am using a Willem's PCB3 programmer and I am not sure how to erase it or what to read and program it as correctly.

 

This is only the second time I've heard of GM using this style chip. What you have is an EPROM in a plastic package. Short of xraying it you can't erase it. You will need to either remove that chip and put a Flash chip or EPROM in it's place. Or use an adaptor board.

The up side is that you have a good stock starting BIN and the correct knock filter and limp mode calibration pieces.

The reason these chips are available is cost. They are a lot cheaper then a hermetically sealed ceramic package with a quartz window.

RBob.