1997 Jeep Wrangler Engine will not start

The 12 volts at the coil for one to two seconds after turning on the ignition switch proves the ASD circuit is working properly. After that, the ASD relay will not turn on again until the engne computer sees engine rotation, (cranking or running). It powers the coil(s), injectors, fuel pump or pump relay, alternator field, and oxygen sensor heaters.

The engine computer knows the engine is rotating by the pulses from the crankshaft position sensor, a common falure item.

Caradiodoc

Replaced the cracnkshaft position sensor, still will not start and not getting any spark

Let me clarify my earlier reply. Check for 12 volts at the ignition coil for the first second after turning on the ignition switch. If you turn the switch on, then run to the front of the vehicle, there will not be voltage on the coil. It is only there for one second, so you'll need a helper to turn the switch or you'll need to prop the meter or test light so you can see it from inside the vehicle. If you never see voltage there, I would first suspect my probe wasn't making good contact with the terminal. If there still isn't voltage, suspect the ASD relay, which you already switched, or the wiring to the coil. The Engine Computer is next, but I'd be surprised if he was the problem.

If the voltage is there for the first second, it must come back during cranking. If it doesn't, that's the time to head to the crankshaft position sensor. Since that didn't help, the next thing to try is the camshaft position sensor. According to Chrysler, his purpose is for synchronizing fuel injectors, but on Chrysler vehicles, this sensor will result in no spark AND no fuel if it is defective.

The cam sensor is in the distributor. You can test it with an old pointer-type voltmeter. The signal wire voltage should pulse between 0 and 5 volts during cranking. If it doesn't, replace that sucker.

Caradiodoc

Ok, so the camshaft position sensor did not fix the problem. I put a voltmeter on the wire to the coil that should have 12 volts on it for at least 1 or 2 seconds. I see about 1.2 volts. I disconnected pulled the ASD relay and put a jumper across the contacts expecting 12 volts at the coil, just a few millivolts is showing. I checked the voltage at the connector near the PCM, saw 12 volts when the connector was separated. I disconnected all the fuel injectors because they are part of the 12 volt circuit from the ASD (thought maybe a short in the injector could be pulling the voltage down, no change. Thinking maybe one of the O2 sensors could be cause a problem? They are feed 12 volts from the ASD?

Based on some observations in your first post, I'm going to strongly suggest there is nothing shorted. If you have 12 volts feeding the contacts of the ASD relay, a fuse would have blown when the relay turned on or when you bypassed it.

If I found 1.2 volts at the coil, I would first suspect my meter probe wasn't making good contact with the terminal. After scratching it around a little, and I still had 1.2 volts, I would measure on one of the injector connectors. If you find 1.2 volts there too, ... Happy day! Suspect a break in that wire. The splice would be a logical spot to look. Coroded splices are especially likely to cause some items on a circuit to have power while other items are dead.

Caradiodoc

I've spent the better part of today diagnosing the same problem. Vehicle is 2000 Wrangler with the 2.5.
Problem is no starting on crank. Looked for 12v at coil but found nothing, no on key on and not while cranking. Tested the other lead back to ground and I got continuity back to all grounds so I knew the computer could control the coil. Tested for 5v reference at crank & cam sensors, those were good.
To verify anything obvious as being faulty I temporarily hooked up a direct 12v wire lead from the battery to the coil green wire, cranked up the Jeep and it ran! Woohoo. I have no idea where the coil's green wire goes or what controls its voltage but to my knowledge this vehicle's ASD system is functioning properly because all the injectors are firing now.

Ends up that the problem was the wire from fuse 6 in the power diistribution center going to the contact side of the ASD was broken, actually it is the wire the comes out of the fuse side of fuse 6 it's a red and white wire, goes past the battery and is spliced at S100 just before the Power Control Module. Must have been a drop of battery acid that spilled on the wire bundle some time ago and worked its way into protective cover of the bundle eventually it burned thru the insulation and then the wire. This is the 12 volt supply to the contact side of the ASD which powers the coil, injectors and the PCM. Re-spliced the wire and everything works fine.

Wonderful. One more veehickel fixed.

How are you doing with yours ibanezjeepguy?

Caradiodoc

Ibanezjeepguy, the dark green wire at the coil comes from the ASD, in fact it is all part of the same circuit that provides 12 volts to the fuel injectors, so when you jumped the coil wire you are also providing 12 volts to the fuel injectors, all the time etc comes from the PCM by turning on and off the grounds to the injectors and coil. I suspect the ASD, or the same problem I had with the wire from Fuse 6. Check the continuity from fuse 6 to the contact side of the ASD, I would disconnect the battery negative first. If you get continuity, then check for 12 volts at the ASD side with the battery negative disconnected. Just put the meter common on the battery negative and the red lead on the ASD contact coming from Fuse 6. If you get 12 volts I would suspect the ASD relay, if you don't start unwrapping the bundle of wires between the battery and the fender.