I got the one that you showed me from Amazon

 

OK great, lets go find out where you loose the ignition pulses that should eventually fire your plugs,

1. Disconnect the wire harness connector at the coil
2. Place the alligator clip of your new LED test lamp on battery positive at the battery
3. probe the coil connector socket for the wht/blk wire from the ICM
4. Crank the engine
5. Does the LED test light flash?

George

 

No pulse at the white/blk

 

OK so that means that the ICM is not generating the control signal to fire the coil. Now we need to find out if the PCM is sending the control pulses to the ICM. Everything gets connected back up and your going to need to pierce the white wire going into the ICM near the connector by either using a piercing probe or carefully peeling a section of the wire insulation back to expose the copper wire (you reseal it with liquid electrical tape later), Using your new LED test light, connect it between this exposed white wire and battery positive and see if you have pulses during cranking.

Note to anyone reading this:

The safest and most revealing test of computer timing signals like this and the output from the crank sensor is an oscilloscope because it gives you great detail and does not load the circuit, so no risk of damage to internal computer circuitry or degrading the waveform being measured. They are also great for analyzing ignition waveforms. Since most diy mechanics don't have a scope, the "scope on a rope" can be useful. Sometimes an old school incandescent test light is actually better like testing the O2 sensor heater circuit because it loads the circuit while testing which can reveal marginal wiring faults better but any time your are testing anything involving computer circuits (PCM/ECM/BCM/etc) and your not an electrical expert, don't use this tool. The LED test light draws minimal current and so it barely loads the circuit. This means that you eliminate the risk of blowing out an internal module component like a ground side switching transistor and bricking the module.


George

 

Have not worked on it for awhile, I had to put my wife in the hospital but she is back home and doing well. I went back checking the S10 but it looks like I will have to get a new starter. The old one has given up. I will check what you said as soon as I can

 

Ok, the coil and icm wires plugged in I pierced the white wire and was putting clip on the battery positive and the moment I touched the positive sparks came out of the coil to the closest metal. Before I did that I put the test light on the negative and touched the white wire to see if it was hot, it was not.

 

What did you connect between the ICM white wire and the battery positive? Your LED test light or a straight wire? If it was your test light your sure its an LED test light and not a std issue incandescent test lamp?

George

 

I used the light you told me to get from Amazon

 

So what likely happened here is that you supplied 5v through the test light to the ICM control input and so it generated one coil control pulse. The distr was then in between cylinder positions or there is a problem with the coil wire to the distr or the distr. Probably just the distr position. The spark had nowhere to go so it found a place. That said, inspect the coil for cracks and test the coil wire resistance.

So now what? there are three ways to test the signal into the ICM:

1. Look at the square wave signal with a scope. Not many here have one of those.
2. The GM manual has you hook up your meter in AC volts and connect between the pierced white wire and ground then crank the engine and look for 1-4 volts AC
3. What we were doing. I should have had you pull the coil wire from the distr and ground it first so the spark has somewhere to go

Either #2 or #3 will work but I was trying to keep this as simple as possible. The fact that ou generated a spark with essentially a control signal into the ICM tells me that the ICM is probably good and there is no ignition control signal on the white wire from the PCM. We should finish this test however.


George

 

Okay I got the meter to ground and checked the white wire with ignition on and got
.35...cranking it was. .75. Once it went to 1.20. No spark at the coil wire. At the pcm is the white wire on the red or white plug in? Ok I may have it, after checking the plugins I was able to push several wires that were almost pulled out, so I am now getting a 4v reading on the white wire and the coil wire is firing. But the starter is now only turning a few seconds at a time. I put in a starter from my old drag car so off to get a new one. Hopefully this solved the problem. I will let you know how it goes!