Thanks for all the thoughts. To elaborate, this model uses the engine
control module (there is no separate ignition module) to control the
coil firing by interrupting the ground. The ECM gets signals from a Hall
effect device (they call it a sync signal generator) in the distributor,
and a CPS. I don't believe the other signals to the ECM (MAP sensor,
coolant sensor) would cause it to not fire the coil at all, they would
just cause it to run really crappy.

I think I have proven that the coil can't be the problem because of the
following test. I jumpered the coil primary leads to the coil so that I
could put a meter across them. When running properly I read 14v at the
positive side compared to battery ground, and about 1v when measured to
coil ground, which gives an idea what fraction of time the ECM is
telling the coil to fire. In failure mode I measure 12v at the postiive
coil compared to battery ground and 0v compared to coil ground. This
tells me the coil is getting 12v but is not being grounded by the ECM,
so it never fires.

So I think I'm at the point where either something is preventing the ECM
from firing the coil, or the ECM itself is bad. I do have a scope, but
it's real dusty and I'd rather not take time to start relearning how to
use it. Is it possible with a meter to tell while the engine is cranking
(not running) if the correct signal is being output from the CPS? Could
I compare the output during failure mode with the output during working
mode and conclude if it's producing any output?

thanks

Mark Leininger wrote:

I have a 92 dodge dakota with the symptom that when the engine gets warm
it loses spark. I have the manual and have followed the diagnostic
procedure to the point where I need to test the output from the ECM. On
this model, pin 19 of the ECM controls the ground to the ignition coil
to fire the plugs at the proper time. The manual says something to
diagnose this that I can't understand. They say to make a little jumper
with a 33uf capacitor that is used to ground pin 19 and ground the coil.
When the ground is removed, if a spark is seen at the coil cable (I
assume they mean secondary), they say the ECM is bad.

Can someone explain the logic of what I'm trying to do. I understand
what the ECM is supposed to do, but I don't understand how to know if
it's doing it, even with this little jumper gizmo they describe. I'm
fairly electronics literate, but not a wiz.

There are no stored error codes at any point in the failure that I have
been able to observe. All help appreciated
thanks