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 -----
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