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Thread: Crank-no-start mystery

  1. #1
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    Crank-no-start mystery

    Recently my 98 TJ 4.0 begin showing the below symptoms:

    After sitting for a while (at least over night, the colder the worse it is) it will crank but not start. It will start usually after the 2nd attempt but if its been a few days it takes more.
    Sometimes it will stall when coming to a complete stop. It will start right back up though.

    I have replaced the IACM, CPS, MAP, fuel strainer, the spark plugs are only a year old, and i thoroughly cleaned the throttle body less than a year ago.

    Any ideas? I have a new TPS to put in but the screws holing the old one in are stripped so i might have to take it somewhere. Any help would be appreciated. Thanks.
    Last edited by Cerrito; 10-21-2018 at 03:30 PM.

  2. #2
    Nothing but a Thing Snboarder113's Avatar
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    Check fuel pressure after sitting. They have check valves that go bad and the gas cycles back into the tank instead of staying pressurized in the line. To test this in the morning turn the key on but don’t crank turn it back off. Turn it back on turn it off. Turn it back on again give it a couple seconds then start. This primes the gas back into the line.


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    thanks, ill try this later.

  4. #4
    Hooked PT1400's Avatar
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    What snboadr said. The fuel prime cycle is up to 10 seconds per key cycle or until the fuel pressure reaches 40 psi. If it takes more than 1 cycle to prime the system you need to have the regulator looked at and probably replaced.

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    Thanks, this trick works so I guess the regulator is bad.

  6. #6
    Hooked PT1400's Avatar
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    Either the regulator is bad, you could have a leak, or the electric pump in the tank is having an issue.

    Check out this video. He's a little rough around the edges but explains what he's doing really well.

    https://youtu.be/nZuSbHWJe7A

  7. #7
    Nothing but a Thing Snboarder113's Avatar
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    When you say you replaced the fuel strainer. What part are you referring to? The issue is internal to the fuel pump itself. Which if you start looking for a new tj pump you’ll find the only options are a new like $500 Bosch unit. But, if you get one for a zj for like a 100 ish you can pop the top half off (the part with the pump) and put that onto the tj’s bottom half. Same plug and all, save you hundreds. Sometimes I hate parts stores.



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  8. #8
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    the paper strainer at the bottom of the fuel pump. when we took the pump out the strainer was completely clogged and a new one was very cheap so i was hoping it would do the trick instead of spending a ton on a new pump as you mentioned.

  9. #9
    Hooked PT1400's Avatar
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    Oooo, pump might have burned up if it had a plugged strainer. Do the testing in that video!

  10. #10
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    Just wanted to give an update for everyone who helped, may help some others. I took the jeep to a shop because after replacing the TPS the throttle began to die and surge on the highway. It turns out that the sensors in the car were not getting enough power to operate properly. The shop adjusted this so that they were getting the correct amount of power which fixed the throttle issue and also fixed the cranking issue. i guess the crank sensor was affected too. to test to make sure that the crank issue was truly fixed i like the car sit without being started for days in consistent 30 degree weather. 1 turn of the key and it started immediately.

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