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Help diagnosing intermittent misfire.

Discussion in 'Wrangler TJ (1996-2006)' started by Raven Gray, Apr 24, 2021.

  1. Apr 24, 2021 at 11:37 AM
    #1
    Raven Gray

    Raven Gray [OP] Member

    Joined:
    Apr 23, 2021
    Member:
    #5568
    Messages:
    5
    Vehicle:
    97 TJ 2.5 Lil Dog
    I have a high mileage (190+K), 97 TJ with a 2.5lt 4cyl engine, throttle body injection, 15 gal tank with I suspect a "20 gallon" fuel pump/filter assembly, manual 5sp transmission with a 4.11 Dana rear end. It's been lifted with a 2" kit and has 32" tires.
    The rig runs relatively well. Starts right up, no noticeable "smoke" in the exhaust.
    But, and there is always a but, after being on the road for a while, (50+ miles at 35+ speeds), it will some times "stutter" or misfire before continuing on fine. A few miles latter it might misfire again and then even out. If it misfires while on the road and I stop, to get gas or pop into a store, I have noticed it (sometimes) has trouble starting up again. It acts almost like its flooded and needs to "rest" before starting up again.
    The last time it did this, it was more serious, I seemed to loss power, and it acted like it was "lugging" in to low a gear. (I was in 3rd gear roughly 23K RMP at 35mph). It would even out for bit, lug again and well rinse and repeat. After about 3-4 miles things returned to normal. Running the "code hack" turning the ignition on and off a few times, only shows a code "12" which if my research is correct deals with a battery disconnect to the PCM sometime back.

    I've seem posts on everything from "plugs to new engine" and lots of abbreviations like bad ECV, MAP, O2S ABC and LMNOP. I don't know the brand or type but the plugs are "new" as are the wires and distributer cap. Its a random thing so it seems like a condition that is a result of driving, or engine warming up or . . .? Oh one other thing, I should mention, at some point it looks like someone removed the "pre Cats" from the exhaust manifold. All that said, here are my questions to the forum.
    Has anyone had similar experiences and does this sound like one thing more then another? Any help in diagnosing this is greatly appreciated. Thanks.
     
  2. Apr 25, 2021 at 5:37 PM
    #2
    Justanotherjeeper

    Justanotherjeeper Well-Known Member

    Joined:
    Nov 1, 2020
    Member:
    #5195
    Messages:
    104
    Gender:
    Male
    First Name:
    Peter
    Vehicle:
    2011 Red Wrangler 2 door
    paid cash for it.
    Intermittent problems are the hardest to diagnose, frustrating and can be expensive so I feel for you brother. First up it doesn’t sound electrical, it sounds like fuel. It could be anything - sediment in a dirty fuel tank, for example. The only way you’re going to solve it is to take a systematic approach to the whole fuel system and solve by the process of elimination. I wish I had a crystal ball and could say oh yeah, I had that once and it’s this. But unfortunately that’s not how problems like this work. Good luck.
     
    LYFZGOOD likes this.
  3. Apr 26, 2021 at 7:02 AM
    #3
    Raven Gray

    Raven Gray [OP] Member

    Joined:
    Apr 23, 2021
    Member:
    #5568
    Messages:
    5
    Vehicle:
    97 TJ 2.5 Lil Dog
    Thanks for the input. My suspicions are with the fuel pump/regulator unit, which I'm thinking was changed at some point since the fuel gauge never shows a "full" tank. Hmmm, 20gal pump in a 15gal tank? Well, fun times.
     
  4. Apr 26, 2021 at 9:01 AM
    #4
    Justanotherjeeper

    Justanotherjeeper Well-Known Member

    Joined:
    Nov 1, 2020
    Member:
    #5195
    Messages:
    104
    Gender:
    Male
    First Name:
    Peter
    Vehicle:
    2011 Red Wrangler 2 door
    paid cash for it.
    Could be a tank issue as well, since the fuel gauge is not working correctly. Rust and sediment build up in older tanks and cause problems.
     
    LYFZGOOD likes this.
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