ALDL data

[Mike Rolica]

your better off in the bank and performance to build your own :)
  -----Original Message-----
  From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf Of
Dave Zug
  Sent: Sunday, September 03, 2000 2:14 AM
  To: gmecm at diy-efi.org
  Subject: Re: ALDL data


  If you have an o-scope and can see a square wave signal between ground and
one of the diag-terminals then you can be pretty sure that its ALDL.  If you
can trap the signal and see if it repeats then you can figger out about how
many bytes are there. if its a really small amount like 8 - 10 then there
probably needs to be a request sent to the ECM for it to start sending
lengthy amounts of data, and the data being sent without this request is
very basic.

  With a DMM, if using like a "John Fluke" 73,77,83 series DMM ($100- $150
range) you can see the voltage bar LCD points pulsing up and down rapidly as
the RMS DC value changes (as a result of the varying duty cycling of the DC
signal based on the characters being represented) in some repeating pattern.

  With an analog needle, you won't see much but a steady DC voltage
somewhere between 0 and 5, needle moving very very slightly.

  I think caddilac had an onboard diagnostic viewing system built into the
RADIO controls system???  Jeffrey M's wife had a car with that system in it.
You might ask him if it was a 95 and to clarify my vague memory.


  P.S. .. anyone out there have flow numbers on a complete stock TPI intake
system, and Accel / Ligenfelter units?  ;-)

    ----- Original Message -----
    From: Jason R. Haines
    To: GMECM
    Sent: Saturday, September 02, 2000 12:22 PM
    Subject: ALDL data


    What is an easy way to check to see if an ALDL port has any data coming
from it at all (if it is wired correctly etc.)? I have a custom car I want
to read the data from but a Tech 1 and a Tech 2 won't communicate (neither
will Diacom). Anything I can check with a voltmeter? What about using the
Diacom cable (parallel port) and some kind of software to see the raw data
(if any exists)? I think I might also have a serial port ALDL cable (for
some other software) that I could use.

    BTW - the engine is a Cadillac Northstar engine with a 1994 ECM (I think
it is ECM part number 16197429) and a custom harness (no Cadillac dash, no
electronic throttle etc.).

    Jason

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