Strange ALDL Blather

[Bruce Plecan]

Maybe this will help?.
Grumpy

>  http://www.geocities.com/ecmguy.geo/diagnostics/do_diag.html

> Remember this is "the chatter", and won't tell you much. The meat is when
> you request data from the ECM. My chatter from my LT1 Z28 looks like this:
> F0  56  F4  C6
> 90  5A  25  00  40  5C  FF  56
> 0A  58  95  03  A5  61
> 90  5A  26  00  40  5C  FF  55
> You can pick apart packets from a datastream by looking for patterns and
> then calculating the checksum. Use Win 95 Calculator, set to Hex and Byte
> mode. Add all digits, hit NOT, add 1. There's the checksum.
> Above, the 25 and 26 are RPM*25 values (925 and 950 RPM respectively), and
> the 40 is intake air temperature.
> When you send it a "shut up" command of F4 56 08 AE you can follow it up
> with a Mode Request, and that should start spitting real data at you.
There
> are quite a few modes, they follow the format F4 57 01 XX CS, where XX is
00
> thru ??, and CS is checksum.
> I suggest using a spreadsheet to look for trends in the data, unless you
can
> find a protocol description lurking about.
> Good luck,
> Andrew


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