[Diy_efi] LT1 diagnostic mode/codes

[Daniel Hiltgen]

I've got a '95 vette LT1 with some drivability issues. (stumbling at low
RPMs and high load)  I've eliminated most probable causes, but when I was
looking through the shop manual diagnostic procedures they call out using
the Tech1 to shut down individual cylinders and check the RPM fluctuation.

I've got pcmcomm, and freescan on my laptop (plus tunercat, but that's
unrelated of course), but all they do is show the basic passive data
stream.  I've looked around but I haven't been able to find a document
that explains all the diagnostic commands you can send to the LT1 PCM to
run active diagnostics.  The pcmcomm program has a "send command" feature,
so I think if I knew the right commands to send, I could manually enter
the various diagnostic modes that the Tech1 would normally go through. 
Even if GM hasn't published them, I have to assume someone has hooked up a
serial analyzer with a Tech1 and reverse engineered all the diagnostic
commands.

Can anyone point me at docs that explain the different commands I can send
for active diagnostics?  I'd like to be able to cycle the cylinders off
and on, cycle the various solenoids, and generally perform active
maintenance via the laptop to help solve my current problem and any future
ones I may have.

Thanks!
Daniel


--
Daniel Hiltgen (daniel at hiltgen.com)
http://www.hiltgen.com/daniel