1. #1
    bcox624's Avatar
    bcox624 is offline Junior Member
    Join Date
    Mar 2014

    Help! I don't know what's wrong.

    I have an 1988 YJ 4.2L I6, manual transmission, with a Motorcraft 2100 carb and nutter bypass.

    I recently swapped the carb from the Carter to the MC 2100 and executed the nutter bypass because the Carter took a crap. It was sputtering and wouldn't start at times. I'm not a mechanical genius but the Jeep (I call her Stacy, lol) seemed to be running a lot smoother and it seemed to have more acceleration.

    Approx. 2 or 3 weeks after I did the carb swap the Jeep started sputtering HARD. It's undrivable now. It'll sputter and the RPMs will drop from whatever they are at to 0 immediately. And unless I hit the clutch or put it in neutral really quickly then it will stall. Also, when I was on the way home the day that this started happening the Jeep had 2 of the loudest backfires that I've ever heard. They sounded like 12 gauge shots. They were approximately 10 or 20 seconds apart and the second one was slightly less loud. Now the Jeep has a really deep idle and it sound like it has an aftermarket exhaust, which it doesn't.

    I took the carb back apart and I couldn't see any clogs in the fuel flow. I could see both of the streams of fuel flowing into both of the barrels when I pushed the accelerator. Now at an idle and I can rev the engine and hold it at 1,500 or 2,000 RPMs without any major sputters. But once I put it in gear and try to go it sputters.

    The only thing I can think to do is the TFI ignition upgrade with the bigger distributor cap because it could probably use a tune-up anyways.

    Does anyone have any ideas, comments, or clues as to what could be causing this?

  2. #2
    importman's Avatar
    importman is offline Junior Member
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    Mar 2014

    Re: Help! I don't know what's wrong.

    I'd be willing to bet it's the ignition module. I just went through the same thing. I did the TFI on mine and replaced the stock module with a GM HEI module that I mounted inside the old module box, (after I gutted the electronics from the box). Google "Team Rush upgrade" and you'll find a wealth of info on this. Hope this helps.

  3. #3
    Tison78_CJ5's Avatar
    Tison78_CJ5 is offline Senior Member
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    Mar 2014
    Marshall, NC

    Re: Help! I don't know what's wrong.

    My first thought is your problem isn't related to the carb.
    Last time I lost power, and could only idle, it was a bad ignition coil. Check the fire on the plugs and make sure it is pretty blue.
    The time before that it was bad timing chain.
    I don't have a book on your Jeep. I am guessing it has the electronic ignition by that year. Check the fire on a plug anyway.
    I am sure with all the Jeepers, some very good mechanics, others will probably be able to give more educated pointers.
    I am just going by what I have seen on other engines.
    Best of luck to ya, Hope it turns out to be something simple.

  4. #4
    superj's Avatar
    superj is offline Senior Member
    Join Date
    Feb 2010

    Re: Help! I don't know what's wrong.

    My friend Jake's jeep does that if the vacuum advance line is hooked up on his Chevy distributor that he runs. And your exhaust sounds like you blew something apart or blew the muffler welds open
    no more jeeps at this time. next time it will be a cj with a v8

  5. #5
    Shewilly's Avatar
    Shewilly is offline Senior Member
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    Aug 2008
    Wine Country North East Pa

    Re: Help! I don't know what's wrong.

    Try ignition module. My 80 cj was doing the exact same thing. fixed it.
    • 75 CJ5 258 I6
    • 80 CJ5 258 I6 stock
    • 96 XJ (RIP Tow-Mater )
    • My other 4x4 has legs and nice "paint"

    To the PO of my 75 CJ,
    I hate you.

    Click here: Truck Night at Yankee Lake - 4x4 Event

  6. #6
    carnuck's Avatar
    carnuck is offline Senior Member
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    Jan 2009

    Re: Help! I don't know what's wrong.

    I had crud in the fuel tank jam the fuel pump inlet valve open and act like this. A filter right before the pump allowe me to see the junk and it kept running. The hoses were all cracked and sucking air too.
    '87 Comanche 4x4 lifted 5 1/2" on 33" tires 4.0L/AW4/NP242 $3500
    Perfect combination but too small to haul my Grand Kids and wife in.

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