I recently tried to order a new memcal from GM, P/N 16155503(5504AWFZ). They told me it was a bad number, but it is stamped right on my original memcal. Did GM discontinue this part number? He then asked what are the last 8 digits of my VIN, so he can cross reference the part number. Now I have a totally different part number 16163138(AXYC).Is this an updated version of the original memcal that came in my car? How many other bad numbers are out there?

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'91 Formula
383CI Supercharged
5-speed
3.42
12.34@117.04
on Drag Radials

There are a couple possibilities here.

One. GM constantly updates proms. Less so for the older cars, but, there can be as many as 15 different part numbers of prom for the same car. (used to work in the parts dept.....)

Two. The number you see is a "casting" number, and not an actual part number. A good parts tech can call GM and get a conversion number for you.

Three. Yep, the number may indeed be discontinued, and no longer on the records.

Hope this helps.