Originally Posted by jwfirebird
i really hoped that was the issue. did you closely inspect the connectors and wires to the pcm. i think you said the pcm was changed as well?
Yes, I did inspect them. I even back probed the connection at the PCM to check for the cam signal and the fuel reference signal. However, that does not necessarily mean the signal is getting through inside the PCM since I can not probe at that point. I would have to locate that point inside and solder a test point to take readings.
I have eliminated the ICM wiring harness, I have switched out the cam and crank sensors; although using the same brand. I did put the original cam sensor back on; it must not have been shorted because the car started or it could be that the guy that told me that did not know what he was talking about. I eliminated the PCM. I have switched the ICM for the original one (swapped out because heat issues may have caused the original stall problem). Note that the car ran great for four or five weeks after replacing the MAF sensor; so the problem occurred after some time of the original repair.
At first the GM shop manual states: "DTC 18 will set indicating an intermittent problem with the cam signal or the fuel control signal" So, bad wires, bad cam sensor, or an internal problem with the ICM. The cam signal and fuel control signal are generated by the ICM and sent to the PCM. Then it mentions that the 18X portion of the crank sensor or bent or missing vanes on the harmonic balancer interruptor rings.
*Same problem with two different wiring harness. (not likely both are bad in the same way and the original was repaired)
*Same problem with two different ICM; possible both were affected by the bad wiring harness in some way
*Same problem with two different cam sensors; possible both were affected by the bad wiring harness in some way.
*Same problem with two different crank sensors; possible both were affected by the bad wiring harness in some way.
Here is a point about the cam sensor, I could test for the cam signal at the back of the PCM connector, and it went from +5 to 0 volts just as it should. So that tells me that the cam sensor was working as it should. That was by rotating the crank by hand. I have not checked with the engine running; running the voltage is less than 5 is all the manual says. As I said before, I really need an oscilloscope to see what is happening with the engine running.
I am wondering if it is something else beside what the GM shop manual is telling me. The manual does not indicate the ICM can be at fault at all. The shop manual I have, I am guessing, is from back in '93. What I was hoping that GM could tell me if after the shop manual was printed that updates or service bulletins on the problem was published.