K-Blazer ECM ALDL data

[Maverick]

First, the vehicle in question:

1993 Chevy K-Blazer, 5.7L V8 TBI, a P4 type ECM that has the number
16168625  and BDJY for identification on the EPROM carrier, two ports of 32
pins each (one red, one blue), and a good old standard 8192 data stream on
the M pin of the ALDL connector.

Been hunting around the net in my spare time for the past week and a half
or so looking for information on my ECM and ways to get more useful data
out of it.  Not really for any particular purpose, just for the sake of
tinkering with something new and maybe being able to monitor a good deal
more variables within the engine. Or, for that matter, to track down some
of those exceedingly rare glitches with the truck.  

Got it all hooked up today, and was getting valid data (was able to send
simple queries like F4 57 01 00 B4) to get mode 1 data packets, but
unfortunately the data I'm getting back doesn't seem to be decipherable.
The response seems to be 3 header bytes ( F4 01 95 , if I remember right -
left my notes back at the garage for the night - pretty sure that's it,
though), followed by 62 bytes of data, followed by the checksum (which does
work out).  Along with some help from a few other friends, tried in vain
most of the afternoon to correlate the data I was seeing with any physical
measurements on the truck, but nothing ever worked out - too many things
changing at once to even begin to narrow it down.

So, first, does anyone have any ideas on the data contained in this stream
or how to go about finding out such a thing?  I assume asking GM will get
me nowhere, otherwise all this would be documented out somewhere.  I've
scoured the net and all the search engines / mailing list archives (as well
as the University's library) and found nothing that comes close to the data
I was seeing - nothing ever matched up well.  If not, does anyone have a
better reverse engineering methodology than just trying to observer
patterns in the data as a result of changing the operating conditions?  

Thanks, and I appreciate any help anyone has on this - I'm temporarily stumped.

PS - on a side note, I also found 9600 baud (apparently) ABS data coming
from pin H - does the ECM also see this data or is it purely for diagnostic
purposes?  Does anyone have a wiring diagram that they could check this?


Nathan




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 Nathan D. Holmes   maverick at drgw.net, ndholmes at iastate.edu
   122 Shepard #3  Box 328  Gilbert, IA 50105  Iowa State University - EE
   http://www.drgw.net/~maverick   PH: 515-663-9368
   Electrical Team, Team PrISUm, ISU's Solarcar Team
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