What was the setting on your digital meter?

George

The ICM white control signal wire is on pin 9 of C3 at the engine computer which is a 32 pin connector. The other 32 pin connectors do not have a white wire on pin 9. Also C3 is the only 32 pin connector with a wire on pin 1 - dk green/wht.

George

Wow you got back quick. I edited the one I sent you so re read it. Thanks

Sounds like you might be there. 4VAC is about right on the white wire while cranking. Good luck.

George

Good news came to a false alarm. No spark from the coil. I reread some of your suggestions and started over checking the wires.
With ignition on I checked the pink wire and the white and it was 13+. I was checking it wrong before as I was using the battery ground to test. Also rechecked the pink wires and all were good. cranking
engine with led test light on the white wire to the icm it would light up and then go out, not pulsing. Each time I turn the engine it would come on and go off. I checked my running s10 (but bad transmission) at the icm, the pink as well as the white/black had 12+ v but the one that won't crank does not. Don't know if that is a clue or not.

Some definitions may be in order to proceed. Lets discuss this diagram (George Draw):

https://cimg5.ibsrv.net/gimg/blazerf...f31437b3ed.jpg

Power to any object in the truck, like the ICM needs to travel from the battery positive post to the object/load and then the circle needs be completed back to the battery negative terminal of that battery. There is no universal ground, only the ground for the source battery. Vehicles sometimes have dedicated ground wires that go back to the battery in critical systems but most of the time the ground for that load makes the trip back to the battery through the frame. Lots of opportunity for corrosion and voltage loss. The whole frame and engine block is battery ground. I think what most people do not understand is that the quality of the ground is just as important as the quality of the power side of the circle. Loss and disfunction can occur on either side. Therefore the load only understands the net power at the power and ground wires right at the load/module. If there are problems on the power side then 12v is dropping on the way. If the ground side is hosed then the ground starts rising above ground/zero at the load. So the ICM might see say only say 8 volts net with 3 volts lost on the power side and 1 volt lost on the ground side. In this scenario the power side would measure 9 volts with reference to the battery ground post and the ground side would measure 1 volt in reference to the battery negative post. All of this only reveals itself when the load is fully engaged and you would discover this poor net 8 volts by measuring at the power and ground wires right at the load with the two meter leads. You then would check both legs to see where the problem is which is to say meter to load positive and then black to battery negative post and repeat on the negative side. OK tutorial over. Next post is answering your latest questions. Stand by.

George

Can you get your test light to pulse on the white wire of the ICM of the truck that runs?


George

Test light on the running s10 is pulsing. Plus the white/blk wire is showing 12+v, the none running has no power to white/blk. Also do any of these wires go to the ignition switch or some relay in the cab. One ground wire to the cab was ground to the firewall to an insulated bolt, moved it to a new spot. Edit: I do not know what I did but now the white/black wire now has power. Do all the wires to the crank position sensor have power? One has 12+v the others have 10+!

OK so now what we know is that there is no timing signal to the ICM from the engine computer so either:

1. There is a power, ground, wiring problem from the crank sensor to the ICM
2. The crank sensor has failed or is out of position
3. The engine computer is defective

Does the truck register rpm’s on the scanner when you crank the engine? Have we checked the power and ground to the crank sensor yet?


George

The truck does not recognize the scanner. All of the wires to the crank sensor show they are hot. 12 +v on one 10 + on the others