Also, a very important point I forgot to make. A problem in a electrical circuit will NOT always set a code but driveability problems will be present. This is where relying on knowledge of proper sensor readings comes into play.

 

Because my phone doesn't have a stereo mic, I tried to point to the position of the last tick. No idea how relevant any of this might be: this may be normal behavior I've just never noticed! My Cherokees are usually pretty noisy beasts anyway.

 

Also checked the NSS again; moving it from D or N immediately cuts the cranking, so it seems to be doing its job OK. We're checking for spark in a few minutes; I'll let everyone know how that goes, although I'm pretty sure I know what we'll see.

The battery in this thing is an absolute heap, so I'm also going to try putting a known-good battery in it ASAP.

Thanks for everyone's help so far!

 

sounds like popcorn! Seriously though, mine pops a little after I shut it off, not like that though.

 

Definitely no spark. Guess it's down to the shop to pick up a better voltmeter than I've got. Was looking forward to putting in new HD tie rod and drag link this weekend, but it's looking like instead I'll spend it checking for 5v and wondering if 0.006mA is the right reading off the ground. Mrm.

 

check the coil pack if you have no spark. what i did with my 93 was i pulled the wire and grabbed the coil where the wire goes and had someone crank it. not the best or safest way but it worked lol.

 

You can't really test a bad MAP but if you floor the pedal while trying to start it may start and cough and belch up alot of smoke before starting. Or you can take/borrow one from a buddy or one of your other cars that will plug in and if it starts yours is bad.

 

Okay, an update: verified no spark at plugs, but do have power going to the ignition coil, and do have power going from the ignition coil to the distributor. [How many volts should I have coming out of the ignition coil, BTW?]

Verified 5v on one camshaft position sensor lead, and about 9v at the other. [I think; the digital multimeter I was using was unfamiliar to me.]

So basically, power is coming into the distributor, but not coming out. The distributor contacts are all pretty charred; I tried to clean them up, but no idea how effective that was.

Other than the distributor cap and the camshaft position sensor, is there anything else that fits the symptoms? For example, if the crankcase position sensor were bad, I wouldn't get power out of the ignition coil, right?

 

I'm going to go buy a new battery and a new cap+rotor tomorrow, but I can't find a camshaft position sensor for the 1993 Cherokee. Does anyone know how I could test mine, or if it's replaceable without replacing the whole distributor?

Also, would a bad camshaft position sensor produce the symptoms I have, i.e. power going into the distributor, but not coming out?

 

About 15,000.

There are two primary terminals on the coil, one that receives 12V from the ASD relay, a second that runs to the PCM coil driver.
The CPS signal tells the PCM when to switch the coil driver to ground and fire the coil.
The secondary (high voltage) terminal on the coil is connected to the distributor.
Where, and what are you measuring?

You can do a spot check of the coil's resistance. Disconnect all wires from the coil, and:
primary to primary- about 1 ohm.
Primary to secondary- no less than 6,000 ohms

A few other things that should be cleared up:

Bad CPS- you'll still have +12V at the coil primary. What you will not have is the coil driver grounding the other primary terminal to actually generate spark.
If you have +12V at BOTH coil primary terminals while cranking, this is a distinct possibility. (if the negative side is grounding as it should there will be less than 12V on the negative primary terminal)

Bad NSS won't cause no spark, but will cause no crank. Also affects overdrive and TCC lockup in later years.

Jeep will start up with no O2 sensor, it isn't even read by the PCM until the engine has run for a few moments.
Shorted O2 sensor wiring OTOH will mess with every other sensor powered by the PCM bus, basically all of them.

If you have a bad battery, deal with that first. Computer controlled engines hate bad batteries.

 

What year is the motor?

 

Replaced the battery and the distributor cap and rotor; no luck, although I'm not too disappointed, since those all needed done, anyway.

Tested the Crank Position Sensor by checking continuity between B and C pins; passed.

Tested the ignition coil resistance; passed.

If anyone has any clever ideas, let me know, and I'll give them a shot tomorrow. Otherwise, on Monday it goes to the shop [and bankrupts me]. Thanks for all the suggestions so far!

Should be a 1993, although nothing would surprise me at this point. This vehicle definitely suffers from Previous Owner Syndrome.

 

Turned out to be the ignition coil. Even though it tested within acceptable tolerances, it wasn't generating quite enough spark. Thanks for everyone's help!