1996, Cherokee Classic, 4.0 L straight-6. For the last few years this has occurred, but as time has passed it is more and more frequent (I'd say now that it happens about 1 out of 15 starts): Turning the key causes all the gauges to illuminate (radio plays, etc.), but turning the key to start won't get any mechanical action going. If I jerk around with the gear shift, roll it around a little bit in neutral and throw it into gear, etc. always fixes the problem, so it appears that it is some dead spot that is causing this. I'm thinking maybe it's the brushes in an old starter, maybe it's the crankshaft position sensor, maybe it's something in the steering column, maybe it's something else.
Has anyone else experienced this, and if so, remedied it?
Bill, the next time this happens try starting it in Neutral.
How comfortable are you with electronics? If you have a ohmmeter you can check the NSS by probing at the relay center. Locate the Engine Starter Motor Relay (relay center under the hood) and with the transmission in Park or Neutral check pin 10 to see that it has a ground. In any other gear it should be open.
(note: I'm using the schematics from a 1998 ZJ, things "should" be similar) It's always a good idea to get the service manual for your year.
Pin 6 gets 12V from the battery through the 40A starter fuse Pin 8 gets 12V when the key is turned to Start Pin 10 gets ground when the NSS detects park or neutral Pin 12 goes to the starter solinoid
For the older (1993) relay center it's almost the same.
26 gets 12V when the key is turned to Start
27 12V from starter fuse
28 not connected
29 goes to the starter solinoid
30 gets ground when the NSS detects park or neutral
It's easier to pull the relay and find out which pin has
12V, and which gets it from the key. From there finding the othes is just a matter of elimination.
Yes, if you jump the 12V battery to the solinoid it will turn the engine over, but it will not start it as there is no power going to the injectors or ignition system.
You can also fool the sytem by grounding the NSS pin. The engine will then be able to start even with a bad NSS. (and even if it is in gear!) not a permanant solution, just a diagnositc trick
But I'll say this again. Without the service manaual all of the above is just guesswork based on two similar model years.
For example, If you send 12V to the NSS you will melt it.
Thanks very much for the suggestions, and while it's not analytic proof, it sure is a good indication that it's the problem insofar as all three of you came up with the same culprit. In addition, shifting into neutral gets it to start about 80% of the time. Other times it takes some monkeying around and moving several components as I mentioned, but it has always started, fortunately. Stopped at the dry cleaners to pick up shirts and stuff last Saturday and it took about 10 minutes to get it going, which was the worst so far (usually within 30 seconds I'll get it to start).
I'm quite comfortable with the electronic diagnostics, thanks for being so thorough with all the details - I do not have a multimeter, but used to have two or three of them (why my ex-wife deserved most of my tools in the divorce is beyond me, haha). Need to buy another one anyway, so this is a good time.
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