Calculating the Checksum and more...

[ChrisBourk at aol.com]

In a message dated 98-09-12 01:08:42 EDT, you write:

<< In the GM roms, the CHECKSUM is just the sum of all of the bytes over a
 particular range. Generally from just after the PROMID, VIN (P4), and
 CHECKSUM VALUE. The results is a double byte.
 
 It just don't get any simpler than that.
 
 TK >>

TK,

Help make it "simpler than that" for me - years ago I worked in the
electronics field but didn't get into E-Proms.  Now,  I find myself wanting to
go in and put a turbo on my BMW 535.  The machanical end is a snap for me but
understanding the electronics is a little harder.  I need to retard the spark
with RPM and enrichen the fuel.  The fuel end is the simpler.  How do I go
about understanding the e-prom on my car's EPU in order to rewrite the advance
curve and in fact make it into a retard curve for the spark??? I guess I could
just piggy back another control unit onto it but I feel like I'm caving if I
do that.  Can you help?  what book to look in what to read??

Thanks,

Christopher Bourke