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Moira i would start your own post so we dont get confused as to who is responding. if you want check the basics like we're getting kevin to do and post your findings on your post.
Kevin, do you hear the fuel pumps prime when you turn the key on?
do you have a single or dual tank setup?
when you first turn the key on does your "Check engine light" come on?
have to tried to retrieve codes from it (if it comes on)?
fuel pump does turn on and runs for a second or 2, has the single tank. engine light comes on with the key
When you try to start I assume motor turns over normally?
Does it fire at all and try to start or nothing?
Do you see any fuel spraying from the injectors while trying to start? If not, pour some fuel in the throttle body and try to start; see if you get a temporary fire up
When you try to start I assume motor turns over normally?
Does it fire at all and try to start or nothing?
Do you see any fuel spraying from the injectors while trying to start? If not, pour some fuel in the throttle body and try to start; see if you get a temporary fire up
Motor turns over normal. Doesn’t fire at all, still no fuel or spark
have you tried to pull any codes? im really lost, cant say ive ran across a no fuel no spark issue that wasnt fixed with the distributor or icm replacement
talk to a friend and going to give you more stuff to check on.
have B+ to the distributor?
What is the fuel pressure?
getting a tach signal from the distributor?
How about injector pulse?
Have all of the fusible links been found and tested?
measured voltages to the ECM?
Connected a scanner?
When things get confusing it helps me to focus on one thing at a time. In this case, I’d suggest figuring out why no spark. I’d wait on fuel until you can get it to fire/sputter when putting starter fuel down the TBI. By the way - how did you confirm there was no spark?
there are 4 connections to ECM which I would check end-end Connector to connector with an ohmmeter with a long lead to make sure there’s no break, short in lines as you’ve said you’ve had various bad/chewed wires in past. + power to the coil from the ignition switch (the B+ which Irish asked about)
if good, then have someone bench test ICM - at this point I wouldn’t assume it’s good just because it’s new.
I've never actually tried to debug an ICM but I thought it would work even if ECM was not connected - not sure. I think all it needs is power, a good coil, and the pickup coil in distributor working. It sends a signal to ECM to tell it things are moving and at some rpm the ECM turns on the injectors and at some rpm it starts controlling timing advance/retard. This is why I was thinking just focusing on spark is place to start as if ECM isn't getting pulse from distributor it doesn't let injectors pulse.
example - if the pickup coil wasn't working - you'd never get a spark and you'd never get injectors going. So your two suggestions on seeing if there is a tach pulse and power to B+ are first two things I'd check.
I googled around & here is a description of function I found - not positive it's same for all GM ICMs, just first that popped up. What I bolded below is the part that makes me believe that as long as the coil has power (and is good) and the pickup coil is generating a signal - a good ICM will create spark.
Basic Operating Theory
Here is a little background information (and I stress ‘little’) explained in plain english, to help you diagnose this NO START/NO SPARK Condition of the distributor. In a nutshell, when you crank up the engine (and the system is working properly):
1. The distributor shaft starts to rotate, inducing the pick up coil to start generating its magnetic signal.
2. This pick up coil signal is sent directly to the ignition control module.
3. The ignition module, upon receiving this pick up coil signal (for all intended purposes it's a Crankshaft Position Sensor signal) converts it to a digital signal that is now sent to the Fuel Injection Computer. This digital signal is called the: Distributor Reference Hi Signal in the majority of the Service Literature.
4. Also, after receiving the pick up coil signal, the ignition control module starts to switch the Primary Current (of the ignition coil) On and Off. As you might already know, it's this ‘Switching Signal’ that makes the ignition coil start sparking away.
5. OK, once the Fuel Injection Computer receives the Reference Hi Signal, it starts activating the fuel injectors and above 400 RPM's, starts to send a 5 V Bypass Signal to the ignition control module. It's with the Bypass Signal that the Computer starts to retard and advance ignition timing with the IC Signal.
6. So, then above 400 RPM's (any RPM above this and the ECM considers the engine as having started) the Fuel Injection Computer starts to control the ignition timing.
Last edited by Sabino56; January 10th, 2020 at 1:16 PM.
January 8th, 2020, 1:59 PM
