ECM Chatter sample needed from 89-91 Cutlass w/ub3

[tester239]

Hey w-body folks,

 

A recent project that I have been working on is trying to install a set of digital gauges out of a 91 Cutlass (with tach) into my S10. Actually, i've been looking into this for quite some time now, but put it off during the first college term..

 

Anyway, I've been looking into it, and finally figured out a small bit of data on this "8192 baud aldl" serial interface with the ECM: The ECM of the cutlass, and supposedly some other GM vehicles, constantly output a small amount of data on the ALDL line. I believe it's about 4 packets of information.. and that's how the gauges unobtrusively get's the engine speed on the same line the diagnostic connector is on.

 

Right now, i'm trying to mimic what the ECM outpust constantly with my computer, to see if I can make my set of gauges will respond. So far, they haven't. I've got an interface built to talk with the display, and i'm using GCar to output hex values. The info i've been going off of is based on this site: http://www.akmcables.com/notes.htm (it seems to be going very slow lately, or down right now... and all the info and the program used it on that site) The main page is here: http://www.akmcables.com/aldl.htm and has the link to the newGCar software that I'm using. And yes, I've scoped out my test circuit to my computer, and it is sending out data.. I also have a logic analyzer to capture data being sent to it.

 

So, here's my questions:

1. When a diagnostic tool is attached to the vehicle, and sends the "shut up" command to the ECM, does the tachometer stop working, and are the gauges smart enough to realise that a diagnostic tool is connected?

 

2. Can somebody with a 89-91 cutlass with UB3 gauges read what the chatter is on their car, and post the hex dump? (while engine running).

 

3. Does anybody know the true format of the chatter? IE: what is what, and what each value means?

 

Any other info on this 8192 baud interface would be much appreciated! I can't seem to find any decent data on it, but i can find a lot on 160 baud :/

[Jcrow]

The tach does stop working, the gauges still work. Also the redline goes away.

[tester239]

found the data stream format: A140. now all I need to do is try it out...