1. #1
    seanzy13's Avatar
    seanzy13 is offline Junior Member
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    88 Cherokee, Won't start, no spark

    I'm at a complete loss on this issue. I've tried a new module, new coil, new module and coil together, nothing gets me spark. When the coil is removed from the module, I'm getting +12v of power at the coil connectors, even in the start position. Theres no question I'm getting power to the coil, but why is it not making any spark? Is there supposed to be a wire attached to the 3rd terminal on the coil?

  2. #2
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    Re: 88 Cherokee, Won't start, no spark

    try cleaning connections on cps
    ALL I OWN ARE JEEPS!

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    Re: 88 Cherokee, Won't start, no spark

    Do you have the 2.5 or 4.0? You can do a ohms check on the Crankshaft Position Sensor.. Spec is between 125-275ohms

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    Re: 88 Cherokee, Won't start, no spark

    I believe the 3rd terminal of the coil should be for a tachometer

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    Re: 88 Cherokee, Won't start, no spark

    Thanks for the info. I have the 4.0L engine. I will check out the CPS. Just out of curiosity how does the CPS tie into the system? Does it send signal directly to the ignition module or to the ECM first? I have a feeling this isn't the problem, but I will check it anyway. What is so strange about this is that, when tested the module is putting out 12v directly to the coil, no question about that. The coil IS getting power. I will check out the cps today and post back with some results tonight hopefully.

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    superj's Avatar
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    Re: 88 Cherokee, Won't start, no spark

    what is that sensor on the transmission. the neutral safety switch? whatever it is, check that one. its a huge pain to take of, fomr hat i heat but they normally cause no start issues for us cherokee guys
    I love my old jeep.

  7. #7
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    Re: 88 Cherokee, Won't start, no spark

    Quote Originally Posted by seanzy13 View Post
    Thanks for the info. I have the 4.0L engine. I will check out the CPS. Just out of curiosity how does the CPS tie into the system? Does it send signal directly to the ignition module or to the ECM first? I have a feeling this isn't the problem, but I will check it anyway. What is so strange about this is that, when tested the module is putting out 12v directly to the coil, no question about that. The coil IS getting power. I will check out the cps today and post back with some results tonight hopefully.
    If I remember correctly there are four wires going to the ignition module. A large yellow, which is 12 volt +/- from the ignition switch, a smaller yellow (or orange I forget) wire which is the trigger wire from the ECU and the green wire which is the tach. wire and black which is ground.
    The signal goes from the CPS to the the ECU, timing is corrected and then from the ECU to the ignition module. The trigger signal is hard to measure with a normal volt meter, it isn't DC and it isn't a true AC so most meters aren't designed to recognize the signal. You may or may not gt a little needle movement with an old analog type volt meter, you may or may not get some changing numbers on a digital meter, but they don't actually mean much and may be minimal. I've heard some of the major chain parts stores have a tester for the module. The module doesn't often fail, neither does the coil. But the connections between the coil and the module can get corroded, hot and may relax some making for a poor connection.
    Like mentioned an ohm test of the CPS will often tip you off, the ohm values on the CPS can also change with the temperature of the CPS. It may test OK cold and marginal hot.
    Cleaning the CPS connectors as mentioned is also advisable, oxidation builds up. The signal from the CPS is tiny, doesn't take much to weaken it. You may also want to check the wires closely that run from the connector to the CPS, there is often a lot of extra wire that can flop over onto the exhaust manifold and cook. I tie my CPS wires to my speedo cable with cable ties and run the wire well away from the manifold.
    DO IT IN THE MUD!

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    Re: 88 Cherokee, Won't start, no spark

    The CPS sends TDC/timing information to the ECM.

    I was just checking out Alldata and it recommends checking the igntion control module before the CPS. Use these to help you.

    Last edited by William1982CJ7; 10-08-2010 at 09:29 PM.

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    Re: 88 Cherokee, Won't start, no spark

    Thanks, just what I was looking for btw. I have tested the module already and its fine, I've even swapped it with it a known good one and still no spark. I tested the connections of the CPS and I get an infinite-330m omhs reading, so I'm guessing thats bad. Sucker sure is a pain in the ass to get to, but I got it off and we'll try replacing that and see if its a go.

  10. #10
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    Re: 88 Cherokee, Won't start, no spark

    Well she is running again. Turned out it was indeed a bad CPS. Replaced it and now its running good. Thanks for the help!

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    superj's Avatar
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    Re: 88 Cherokee, Won't start, no spark

    great. i love my 87 and would be bummed to have to keep trouble shooting it and finding nothing
    I love my old jeep.

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