ECM fault?

[Akselrud, Boris]

Espen,

Excellent advice! I like the idea of eliminating ECM for test purporses.
Could you tell me more details on how to start the engine, feed it propane
and then cut off the ECM, leaving the ignition system working? What do I
need attached to the propane tank, some kind of pressure regulator? If this
works, it would indicate for sure that engine mechanicals and ignition are
not at fault.

These are on my immediate list to check:
- ignition system steadiness;
- EFI system oscillation;

Regarding the last one, I did the following:
soldered a switch to cut off MAP sensor and switch to a steady resistor
divider which has the same voltage as MAP sensor at the time. Thus I
eliminated MAP sensor signal and ubstituted an equall voltage to ECM.

Guess what: It makes no difference. That's why I was asking if the program
in ECM could be written such that it causes oscillation???

I did not mention that before, but oscillation can be felt at higher RPMs,
say 1500-2000, not only at idle. At these RPM it has lesser effect, but the
same period.

-----Original Message-----
From: Espen Hilde [mailto:mwichstr at online.no]
Sent: Tuesday, November 09, 1999 6:47 PM
To: gmecm at efi332.eng.ohio-state.edu
Subject: Re: ECM fault?


Hi!
Just brain storming here....Run the engine on propane gas ,use a hose,
,disconect the fuel supply .Does it have a MAP sensor? maybe the EFI
system occilates , try press the hose atached to the MAP sensor until 
its allmost shut. Is the ignition advance steady?
Espen