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Thread: 89 comanche, crank ok, fuel ok, no spark, no inj. pulse

  1. #1
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    Question 89 comanche, crank ok, fuel ok, no spark, no inj. pulse

    I have a 1989 Jeep comanche, 4.0L, automatic, 2WD. Been troubleshooting the crap out of this problem for 2 weeks now with no luck.

    I have good fuel pressure, and the engine cranks ok, but I have no spark and no inj. pulse.

    The crank sensor was replaced summer 2002, and still tests within spec (resistance 205 ohms).

    The camshaft position sensor was also replaced summer 2002 and when tested the voltage cycles when the engine cranks, so I'm assuming it's functioning properly. My manual says it should have about 5 volts, but mine has 7.2V, and will drop to 2.0V, then back up to 7.2V. I'm assuming since it is cycling the sensor is working properly, eventhough the voltage is slightly higher.

    I have also replaced the cap, rotor, plug wires, ign. control mod., the inj. coil and the even the computer (ECU) with no luck.

    Any thoughts? Anybody have similar problems or know of a potential solution?

    TIA,

  2. #2
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    give this a shot.

    loosen the bolts that hold the crank sensor on.

    have someone push down on the sensor from under the hood as you crank the bolts back down.

    after doing that. run a ground strap from the body to the negative terminal of the battery.

    if it still doens't work, check the actual pins on the harness under the dash where the CPS plugs into the ECU.
    everyone sucks... especially YOU!

  3. #3

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    Definitely check the engine block ground. A guy over at the MJ group was going insane with a no spark issue and it turned out to be corrosion at the grounding strap. Good luck!
    Jeep on!
    --Pete
    -88 MJ; ex-2wd, 4.0L, ~5" lift, TJ ax15/np231, '78 Ford axles, custom bumpers/rollbar/sliders, 33" trXus M/Ts, the list goes on and on...
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  4. #4

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    you have a bad crank sensor. resistance measurements dont diagnose very well. if you follow these steps you can properly diagnose a crank sensor:
    1. the first thing you need to do is see if you have spark. If you do, your crank sensor is not bad.
    2. if no spark, check for voltage at both pins of the ignition coil (mounted to side of engine block below #2 spark plug) one pin should have voltage, the other should be a ground but im not sure which is which. that doesn't matter though. if one pin has voltage then the crank sesnsor is not bad!
    3. if there is not voltage on either pin of the coil wire connector then you need to disconnect the crank sensor connector (behind throttle body, 3 pin connector) jump the 5 volt source wire to the signal wire on the harness side of the connector with a paper clip.this is where you say:"huh?" and I say: I think that the source wire is orange and the signal wire is green. The black with blue wire is the ground wire and you do not need to use this one here. can anyone else verify the wire colors? anyways, with the wires shorted together check for voltage again at the ignition coil connector. you should now have voltage and your crank sensor is bad. let me know if my description makes any sense.

  5. #5

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    you have a bad crank sensor. resistance measurements dont diagnose very well. if you follow these steps you can properly diagnose a crank sensor:
    1. the first thing you need to do is see if you have spark. If you do, your crank sensor is not bad.
    2. if no spark, check for voltage at both pins of the ignition coil (mounted to side of engine block below #2 spark plug) one pin should have voltage, the other should be a ground but im not sure which is which. that doesn't matter though. if one pin has voltage then the crank sesnsor is not bad!
    3. if there is not voltage on either pin of the coil wire connector then you need to disconnect the crank sensor connector (behind throttle body, 3 pin connector) jump the 5 volt source wire to the signal wire on the harness side of the connector with a paper clip.this is where you say:"huh?" and I say: I think that the source wire is orange and the signal wire is green. The black with blue wire is the ground wire and you do not need to use this one here. can anyone else verify the wire colors? anyways, with the wires shorted together check for voltage again at the ignition coil connector. you should now have voltage and your crank sensor is bad. let me know if my description makes any sense.

  6. #6
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    Cool

    1337j33px0r-
    Sounds easy. Will try. Thanks.

    Pete -
    I had the same advice come from another forum regarding the ground strap issue. I will have to investigate that problem.

    eighty1toyota -
    With my voltmeter, I verified that I have 12V on the + terminal of the coil and that - terminal is grounded. Are those the pins you are talking about? The terminals that make contact with the ign. control module that rests below the coil?

    Will post my results when I get a chance to head back into the cold, cold garage.

    Thanks.

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    Thumbs down

    None of the suggested solutions worked. At this point I have to suspect the that the crank sensor is at fault, eventhough it was recently replaced. I'll have to call the dealer, pick up a crack sensor install it and hopefully here the engine fire up. Thanks for the advice.

  8. #8
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    if you have access to an oscilloscope, you can test the crank sensor by plugging it into the scope, setting it to 0.2v/div and watch the output, you should see a somewhat triangular wave with a missing peak every 4 or 5 cycles (iirc)
    everyone sucks... especially YOU!

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    Cool

    An oscilloscope? Cool! Now we are making this interesting. I haven't had to use one of those since Physics 101 lab in college. I used to know how to use one. I'll have ask around work to see if anybody has one I can borrow. Thanks for the help.

  10. #10
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    If ya don't happen to have an o-scope layin' around ya can do it the cheezy/easy way and use a $4 harbour freight DVM.
    Disconnect the CPS, set the DVM to the lowest VAC scale & have someone crank the motor while ya measure the voltage generated by the CPS as the motor is cranked. .5 - .8 VAC.

    Basic Sensors Diagnostics - CPS near bottom of page.

    NAPA also carries the CPS's.
    "...the advice given above is somewhat arrogant and in some cases wrong..." . (I'm not an expert... I just play one on the internet.)

    Another Freakin' Jeep Cherokee Website. _____________ Sure you're smart... but do you have what it takes to make "The List"?


    1990 XJ

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    Icon310

    I'm sure you've already figured out that the coil / ICM / IPM (ignition control module / ignition power module) is not mounted on the engine. These don't go bad that often. I have my original 87. Anyway if you want I can email you the MPI handbook. It's 1.43 meg pdf format. It explains how it all works together to make the XJ/MJ go. PM me if you want. Let me know.
    1987 MJ 4.0 Long-bed, 2wd to 4wd conversion, 4.11 axles, 4x4 Posi-Lok controller, 31 in Goodyear ATs on '99 TJ canyon rims, M.O.R.E. Bombproof motor mounts, AX-15 transmission conversion, NP 231 w/ JB Conversions SYE, factory sport bar and light bar w/ MOPAR 6x8 Bosch driving lights, Hella 550 amber fogs and headlamp conversions, factory nerf bars and hidden winch adapter, factory bucket seats, '91 XJ tach and speedo cluster conversion, OPTIMA battery, h.o. alternator, JET HOT coated BORLA header, RANDOM high flow cat, gloss black powder coated valve cover and engine trim, MOPAR street hemi orange block, slightly polished ports and intake, MOPAR ss oversize back cut valves w/ bronze valve guides, level 1 MOPAR valve springs, push rods, and heavy duty rockers, Schneider cam and lifters, Cloyes double roller chain and gears, cross drilled and polished crank with hand matched .002 main bearings, MOPAR Melling high volume oil pump, MOPAR engine oil supplement, ARP fasteners everywhere, Custom 1 inch spacer with over bored RENIX Throttle body, GDI 3 core 4.0 HO cooling system and stock '96 XJ electric fan

    1996 XJ Classic, 4.0, 3.07 axles, AX-15 5 speed, NP-231 dead stock except for the OPTIMA battery w/ HO alternator, POWERAID throttle body spacer (worthless) and GDI three core radiator.

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