Question about 1998 Jeep Cherokee

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1998 Jeep Cherokee has no spark. I would really like to know who the ignition system works. As I understand it, some voltage (from where?) is sent to the crankshaft position sensor. The sensor then sends a fluctuating signal to either the ignition control, ECU, or camshaft position sensor. Eventually, a signal gets sent to the ignition module attached to the coil. The details of this a just a bit fuzzy. I am most interested in understanding the principles involved (first this, then that - order of operations stuff). This will help me troubleshoot.

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  • clinton_comb Nov 16, 2009

    I have a good meter. Unfortunately, the Chilton's manual is not much help. It gives me detailed instructions on simple issues but is lacking on schematics and electrical detail.
    I have discovered that I do not have 12v to the coil when in run position. But, which wire should have 12v and which is the negative signal wire? Alas, my schematic only shows one low voltage wire going to the coil. Does this car have both an ignition module and ECU or does the ECU do both jobs?

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  • Jeep Master
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Sounds like you have a fairly good grasp of what you need to know. Now, get yourself a chiltons or haynes manual for test procedures and expected values. To do this you will also need a decent multi meter (digital).
Do the testing as outlined in the manual and very likely, you will find the problem. There are some components you can't reliably test, but by the process of elimination you can work around that. The most common failure in that system is the crank position sensor, but it's a real pain to replace and so, don't do that without testing and verifying it's bad.

Posted on Nov 15, 2009

Testimonial: "While your first reply didn't give me enough, your follow-up was great. Thanks for the schematic."

  • Richard Scordino Nov 16, 2009

    Thanks for the low rating...you are the 19th out of 4,000 problems I've responded to who chose to do that. (rather sad)
    If you expected a verbal description of a complex wiring system, no one will do that online. Jeep used a couple of different systems including one that employed an ignition module but I don't believe you have one. You did not post the engine size and actually gave better info in your second post. If I knew how far along in your testing you were, I would have responded differently (you made it sound as if you were studying info but had done no testing) i am sending you a wiring diagram for the 4.0 system (most common) If you have another engine do some research and likely you will come up with what you need. The inline 4cyl is very similar to the 4.0 except for the number of injectors. If I remember correctly, the coil pulls power from the alternator circuit but do not quote me on that, check the diagram!!!
    Good Luck!
    http://www.scribd.com/doc/18999822/Jeep-...

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