Here Goes (son's Jeep) Son turned key and it went all the way forward. No start. First move - call dad. Dad (me) spends half day discovering what anti-tamper torx bits are. For a mere C-note, bought and replaced both ignition switch and lock cylinder. Turning key was very tight and mushy, but started right up. Son drove it for a day (has a pool maintenance route). Had several starts he says were "weak starts." Day 2:jeep won't start. First move - call dad. Took starter switch back and got 2nd new one. Installed, turned key (again a little tight and mushy) Jeep started right up. Running fine. Turned key off. Turned key back on and nothing. Dead again. This is day 5. Both of us can now remove/install ignition switch blindfolded with boxing gloves on at record speeds. Several times he has gotten it to start, and it runs for several seconds and dies. Can't bring it to your junk yard in Arizona unless I can get it to start and run in Texas.
A few basics, the ignition switch activates various relays. As soon as the key is turned, the computer closes the fuel pump relay (for a few seconds) to prime the injector rails and closes the ASD relay supplying current to the ignition coil and alternator (among other things). As soon as it starts and the computer gets a pulse signal from the crank position sensor and the sync sensor, it closes the fuel pump relay again, pressurizing the fuel rail, then signals (pulses) the ignition coil to make spark.
If the crank position sensor is bad it will usually supply no fuel or spark. Though if the crank position sensor is weak or partially shorted, function can be iffy.
Export models have modules that interrupt the ASD (auto shut down) circuit. It works with the remote door lock opener as an anti-theft device.
You have to figure out if you are getting fuel, getting spark and getting air. The idle air controller is a piston controlled by the computer that bypasses air around the throttle plate, during start and at idle when the throttle plate is closed (your foot is off the gas pedal).
I've had my 96 start intermittently and run like crap (barely run) when it did start. It turned out to be short in the crank position sensor.
I also had it do just about the same, whne there was a bad connection at the module, worked by the key fob door opener. The bad conection at the door opener/anti-theft interruptor was for the ASD relay.
I've also had my IAC stick closed and the motor would often not start and if it did start would stall almost immediately. A little cleaning and spray oil lubrication cured that.
I've also heard a bad sync sensor, will do the same thing or at least much the same results, though I've never had that problem myself.
Could be other things, but these are a few of the more common. If it is a fuel issue, there is a pressure fitting on the fuel rail, where the pressure can be measured. Could be as simple as a bad coil to cap cable that is partially shorted or open, or a really badly worn distributor cap.
NAXJA.org has a bunch of info for most anything Cherokee related. Using the search function will likely turn up enough reading for weeks. Alldata.com has most all of the tests you can do, locations for most all of the sensors and wiring diagrams for a fee. Worth it in my oppinion. PM me for some PDF. info that may be helpful.
