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TJ no umph cuts out at 2800-3k

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  • #16
    Sooooooo, back to sqaure uhhh 4. Put on new mopar, drive it down the street about 3 miles, poof, limp mode again. Bring her home, slap on brand new computer Wranglerfix loaned me, no better. I did take note the factory computer was fairly hot. Slap in Taiwan CPS, purring like a kitten. So, new computer, old CPS, ran great about 3 to 4 miles, right back into limp mode. Only codes are for cylinder misfires. Hmmmmmmm. I am tempted to swap the harness, I mean I kind of boogered the plug on this one. Works fine but I need to put a new one on there.

    Anyone know what swapping the CPS does to the computer to make it reset?

    Oh and I thought what is that in square plastic thing on the ground. Put in new CPS, dropped bolt, right in the **** bell housing. Luckily it landed in the front just behind the shield. I was able to loosen enough bolts to drag it out with my finger. I uh reapplied the CPS grommet and then put the new CPS back on. Oh I would have been mad if I had to pull the tranny.

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    • #17
      I once had a VSS failure that caused similar symptoms.
      Another time i had to replace the wire harness to the back of the instrument cluster, gauges we’re going nutso and it had similar symptoms.

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      • #18
        Originally posted by mmmmbeer View Post
        I once had a VSS failure that caused similar symptoms.
        Another time i had to replace the wire harness to the back of the instrument cluster, gauges we’re going nutso and it had similar symptoms.
        Gauges are spot on nothing weird there. My buddy said he replaced the coil pack one night, didn't fix the issue so he took it back. I think there is the possibility he didn't reset the computer so it was staying in limp mode. It is odd that every time I swap on a CPS it resets it, runsssss fantastic, well for about a mile or two, drops back into limp mode. Honestly I tried leaving the positive cable off for an hour and that did not reset the computer. The CPS swap and relearn is the surefire way to reset it which is bizarre.

        My codes
        p0353 ing coil cir
        p0304 cyl4 misfire
        p0300 random mult mis det
        p0303 cylinder misfire det

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        • #19
          Wow I'm reliving nightmares reading this. Mine had so many wiring issues. Mopar CPS is the way to go, I learned that the hard way. Mine had a short in the harness right behind the valve cover, in a ground wire. Also a short coming out of the under hood fuse box. 2000 Wrangler 4.0. Mine had same injector misfires. Bought an injector tester and all tested fine. You are having a grounding issue. The computer pulses the ground to the injectors to fire them based on cps position.

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          • #20
            Originally posted by Rubi03con View Post
            Wow I'm reliving nightmares reading this. Mine had so many wiring issues. Mopar CPS is the way to go, I learned that the hard way. Mine had a short in the harness right behind the valve cover, in a ground wire. Also a short coming out of the under hood fuse box. 2000 Wrangler 4.0. Mine had same injector misfires. Bought an injector tester and all tested fine. You are having a grounding issue. The computer pulses the ground to the injectors to fire them based on cps position.
            I have chased a lot of that down. Oh don't get me wrong there could be some chaffing somewhere. I won a low mile 03 engine harness off ebay for 100.00 yesterday so maybe that will be the trick. I did do a fair bit of damage pulling the harness apart and testing things but it still the same as when I got it. When the computer resets and it is running fantastic, its firing 3/4. The minutes it drops into limp mode it quits firing those two. I think, somewhere in that harness, around 3//4 the ground and hot maybe touching. I swear when testing the ground wires I touched the always hot wire, and picked up a reading of continuity. I need to check that again in a minute. Like I was on the ground pulse wire at the connector, and pulled a reading at the always hot at the manifold injector. Would make sense as to why the computer got so hot when running. Who knows, got to be something stupid.

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            • #21
              LOL. I am not declaring a win yet, buttt, drove it about 10 miles tonight and noooo limp mode. I slapped a Ebay coil pack on it and some fancy new double iridium plugs. It ran right the minute a cranked it. Time will tell I guess. I do have an entire engine harness in the garage and a really nice battery cable set. I love deals. Also, who would of thought the original 5 spokes would look good OD green with some 31s on them. Now, getting these freakin flat fenders finished out and painting the beast. I swear everytime I build one they get smaller and smaller. I love sliding into the seat with no effort. I think I will be in it for 5500 which is not to bad for a finished project.

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              • #22

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                • #23
                  Thanks for the write up. Learned a few things reading this.

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                  • #24
                    Your welcome. I drove it to the car wash last night. Still running good. I think the middle coil was shorting and causing the computer to not inject fuel into those cylinders. The biggest problem was listening too a guy that doesn't know anything about these Jeeps tell me what he replaced and took back that didn't work.

                    I had a VW bug one time that would run great for about 20 minutes and then die. It was maddening. Turned out it was the coil. When cold it was touching, but as it heated up it separated just enough to die. I need to look at the plugs I pulled also. I bought the 100k mile recommended ones, Autolite XP985. Whatever it had in it from Champion was not what I remembered being recommended and apparently they can be fickle.
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