according to trax's article the 89 ecm needs a 27C Eprom, at the jadeco site they have these but listed with either a -12 , -15, -20, -25 which one is correct or what is the difference in them?

 

Get the AT29C256's from JDR.com

The 27's are not Flash Proms.

 

other than being the flash prom is the AT29C256 the same as the 27c128?

 

No, the 128 has half the memory of the 256.

 

If you mean that the part numbers were 27C1228-12, 27C128-15, 27C128-20 and 27C128-25 then that is the speed (response time) of the chip. -12 = 120 nanoseconds and is faster. -15 = 150 nanoseconds, and 20 = 200 nanoseconds, etc. Faster usually (but not always) is more $. Slower works fine in these.
If you use the 27C series you will need to use a UV eraser to clear the chip. If you use a 29C256 it is electronicaly erasable, but has twice the space as a 128, and you will need to program your 16k bin into the last (upper) half of the chips addresses.

 

ok how do you program the upper half of this if the car was orriginally designed to work on the 128, do you just fill it with garbage, or will it actually use the info to do it that way? if I can use these and erase them electronically then it saves me from having to purchase the eraser.

 

Get the flash, save your money on the eraser. Just 'stack' the bin, look around on the site, you'll see reference to it.

 

I found an article on stacking the prom after I had made that last post
Thanks