I will be glad to help you get your truck fixed but we need to get some terms down so that we can communicate effectively. Since we are heading towards a proper diagnosis for your lack of spark I will combine some terminology with a lesson on how your ignition system works since this is no spark week here on the Blazer channel. I am in the process of writing an article on this complete with testing procedures, but for now:

Your crank sensor sends a low voltage (12v or less) series of roughly square wave pulses to the engine computer in time with the engine rotation to tell the computer where you are in the combustion cycle. The engine computer then sends a series of low voltage pulses to the ICM and that module then switches the ground side of the coil power on and off. When the coil ground side is closed, the 12v power to the coil is able to charge the primary coil winding all the way up. When the computer pulse tells the ICM to open the coil low side, the field collapses in the coil primary windings and in doing so it creates an induced extremely high voltage in the coil secondary windings and that comes out of the coil high voltage (25,000v) lead to the distributor. This happens because of the ratio between the coil primary and secondary windings. The distr then makes sure that each high voltage pulse out of the coil high tension lead is always routed to the correct plug through the plug wires to each respective cylinder. This is accomplished through proper distr installation in reference to the cylinder sequence via the cam drive position. In order for all of this to work properly, and in the order that it happens in:

1. The crank sensor must output the required pulses as the engine rotates which needs a good sensor, proper sensor gap to the reluctor wheel, proper sensor power, sensor ground, good wiring and connectors. It is often not the sensor especially on an older vehicle.
2. The engine computer has to be able to read those pulses which requires a good VCM/ECM/PCM, good module power and grounds, good wiring and connectors
3. The ICM has to be able to perform the coil ground side low voltage power switching which requires a good ICM, its power and ground, wiring and connectors
4. The coil has to be good and have good power and wiring back to the ICM
5. The distr has to be oriented correctly with reference to the cam drive and ultimately the crank position and be able to get the sparl all the way to the cylinder in proper time and at the correct voltage (rotor, cap, wire routing, wires, plugs
6. Lastly you cant have any killer mechanical defects in the engine

OK so that's a mouthful and where do we go from here? It sounds like you have confirmed that there is no high voltage spark out of the coil high voltage lead when cranking the engine so the problem is either the coil itself, the low voltage control sequence from crank sensor to ICM. There is no best way to approach this so some mechanic dealers choice on the order is OK, but here is what needs to be verified in the order that I work:

1. Is there spark out of the coil high voltage lead during cranking. If yes then move on to the output from a couple of distr high voltage wires. If not (like your situation) then
2. Measure the voltage level on the coil pink wire with reference to (where the meter black lead goes) battery ground and the voltage on the ICM pink wire with reference to ICM ground. If not then find the wiring fault. If ok then
3. Is there low voltage switching pulses happening between the ICM and the coil. If yes then remove the coil, measure the two windings for resistance to confirm and then replace the coil. If not then check the wiring then if OK:
4. Are there low voltage pulses going into the ICM and if yes, replace the ICM, if not check the wiring and then:
5. Are there proper crank sensor pulses going into the VCM/ECM/PCM and if so then the computer is suspect but this is very rare. If not then check the wiring then:
6. Check the crank sensor power, ground, wiring, shim depth and then if all OK look for pulses at the output of the crank sensor

Thats a lot and if your not used to all this probing, measuring, flow chart following and so on then you might be in the parts cannon camp. Not my thing but the order would be:

1. Replace the coil
2. Replace the crank sensor but you will need a relearn
3. Replace the ICM
4. Replace the VCM/ECM/PCM

If you are not a seasoned automotive diagnostic guy then lets start simple. Measure the coil and ICM power and ground and test the coil primary and secondary winding resistance. If your a parts cannon guy, replace the coil.

I'll stick with you as long as you want and help you.


George

 

Thank you, I went back to the battery and need to get it tested, holding a charge until I crank it over.
I have been out of town on a job so I am back on it. I will read through your post. I really appreciate it sorry for the delayed response.
Bruce

 

new update it turned out to be the coil pack. thank you for the help!!!!

 

Glad your fixed up


George