[OnceBitten]

Jeep is a 1997 Wrangler 2.5l 5spd

I have a rather perplexing crank and no start condition on my jeep. It was working fine with no issues one month ago when I last drove it.

Things I have tested:

1. No spark coming from ignition coil
2. Less than 1 volt power going to input side of ignition coil when cranking
3. There is continuity between Pin A7 on the PCM wiring harness and the ignition coil (So not a wiring harness issue?)
4. ASD relay does seem to energize when car is keyed on and I have tried swapping it with the horn relay to no effect
5. Fuel pump does prime when car is keyed on
6. Crankshaft position sensor and ignition coil have both been tested and swapped with new parts to verify their function
7. The MIL does flash on when car is keyed on and the Key on/off trick does not return any codes being thrown.

So, it seems that the only thing left to do is swap out the PCM but I really don't want to spend that kind of money just throwing parts at it until I have a better idea what is causing the problem. Anyone have any guesses or further tests I can run?

[Jerry Bransford]

One side of the coil should get a constant +12 volts, the other side of the coil gets a pulsating ground connection from the engine computer which is what actually generates the spark. Each time the coil gets a ground connection from the engine computer, a spark is generated. Does that help with the troubleshooting?

[wushaw]

It sounds like your not getting power to several systems. Power delivery issues.

[OnceBitten]

Originally Posted by Jerry Bransford

One side of the coil should get a constant +12 volts, the other side of the coil gets a pulsating ground connection from the engine computer which is what actually generates the spark. Each time the coil gets a ground connection from the engine computer, a spark is generated. Does that help with the troubleshooting?

That does help a bit, I was under the mistaken impression that the PCM controlled the voltage end of the circuit, not the ground. So what should I see when probing the harness that goes to the ignition coil when cranking the car? A constant 12 volts on one wire and the (alternating) ground at the other? At the moment I am only seeing approximately 0.3v delivered to the ignition coil so something is definitely wrong. Is the constant 12v source controlled/coming from the ASD relay then? What could be causing the low voltage I'm seeing?

Originally Posted by wushaw

It sounds like your not getting power to several systems. Power delivery issues.

Yeah, I just wish I knew why.