96ckeecntry

My jeep wont start, even on starting fluid. I've verified that my coil is not giving any juice to my plugs. From here I started looking at the cam and crank sensor signals on a fluke scopemeter. I can see the 0-5v square wave going up and down as I crank when I probe the crank sensor output wire. I have a good solid 5v signal as I crank to the crank sensor, and the ground is stable around 100mv.

I ran the scope tests on the cam sensor and the output signal wire from the cam sensor gives me nothing at all. Power and ground wires to the cam sensor appear to be fine while cranking.

Before I go out and buy one or both of these sensors I wanted to ask someone to confirm how the pcm controls the coil output based on these two sensors.
Which of these is true:
1. PCM looks for parallel signals from cam and crank sensor and when it has both it turns on the output for the coil.
2. PCM looks for series signals from cam and crank sensor and when it has both it turns on the output for the coil.

The key difference here is that if #2 is true then a weak or degrading crank sensor may cause the cam sensor to appear as if it is broken when it really is fine.

If you can't tell i'm trying to test all this stuff out as thoroughly as possible to avoid wasting money on parts which aren't broken. Trying to train myself to be a better troubleshooter at these things.

Thanks for reading my thread.

CCKen

I don't have diagrams for a '96 but I think the '96 is only one step behind the '97, which I have diagrams for. I do have a pic of the '96 PDC however.

The Cam Sensor and the Crank Sensor signals are wired in parallel. The sensor's grounds are series parallel.

But, when the PCM sees the crank signal it will activate the ASD relay, which sends a voltage (battery bus) to the PCM to let it know that it is on line. This same voltage is used to power the fuel injectors and the ignition coil. The PCM ignition coil driver cycles the ground to the ignition coil based on crank position and the fuel injector ground drivers are cycled by the PCM based on the cam sensor position.

A quick check to see if the ASD relay is defective is to swap it with the Aux Fan relay or the A/C Clutch relay and see if it cures the problem. If it does, you know the next course of action. If not, further troubleshooting will be requird.

96ckeecntry

I did the relay swap as you suggested and there was no change.

I went ahead and replaced the stator/pick-up assembly/camshaft sensor unit along with a new distributor rotor and expected the car to start right up because it was the last things on my list. I was immediately disappointed when it did not, lol.

I remembered seeing last week that my oxygen sensor wires got caught in the steering rack and one was frayed. So I bought a new oxygen sensor to replace it. Still wouldn't start.

I found that fuse 20 was blown. Replaced it and the jeep started right up. Runs fine.

So here's what happened. Generic bosch oxygen sensor kit (the one with the box and twist crimps) with too long of a harness got stuck in steering rack and frayed the wire to the point where it created a short circuit against the steering rack. Pop went the fuse and out I hopped to start pushing.

The oxygen sensor I bought today was a oem fit and I ziptied the harness up out of the way to hopefully keep that from ever happening again.

I'm still not sure why I could not see a cam sensor signal on the scope. Either way now I know that the cam and crank sensors are set for a while. I'm sort of pissed at myself for not checking the fuses earlier.

thanks for your assistance CCKen

CCKen

Fuses will bite you on the **** that's for sure. LOL

Where is fuse F20 located?

96ckeecntry

F20 is in the fuse/relay block under the hood. It's directly below the aux fan and ASD relays.