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  • Timing Chain

    I think the timing chain is bad in my 89 yj with a 4.2. Before I take everything Apart I want to make sure that that is the problem and it is nothing else. can anyone help me on proving that is what it is. I checked the timing with a light and the line was real eratic and did not stop moving. Not to mention the car runs like $#^* and stalls every once in a while. The car runns rough, and shakes a little at 800-1200rpm then smooths out at 1300rpm up. don't know if it helps but the car is an auto

    sorry about the long post

  • #2
    before you go with your timing chain check your distributor out, under the cap and rotor, advance weights and springs. after that, yank it out and check the distributor gear. they often wear or just get loose on the shaft, NAPA stocks them for pretty much everything, thats how often that happens.

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    • #3
      On my 88 yj every time I accelerated it would spark knock. The timing was set to the correct specs. It got to the point where I could'nt even take off without it knocking. I found out you can put a 6 cyl. GM distributor in it. Cured my problem. I was told jeep distributors are prone to problems.

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      • #4
        How many miles on it?

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        • #5
          carb/vacumn leak

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          • #6
            The carb /vacuum leak was the frist thing I checked. It has around 53,000 miles on it original

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            • #7
              If its the timing chain the erratic behavior would only occur at idle, when theres lash (sloppy chain) beween the cam and crank. Under load the timing would be consistantly off a couple of degrees. The easiest way to check is pull your plugs. Put a compresion meter that will hold cylinder pressure on the no1 and bring the timing mark around to whatever a 4.2 is set at for static advance. I have a 4 banger so I don't know if yours is 0 or not. Once your at the static setting, (no1 will be at TDC and the pressure will be at its highest, any farther and pressure should start dropping) wigle the crank back and forth slowly with the wrench while watching the timing mark and the compresion gauge. If you can move the crank more than a degree or two back and forth without the pressure droping, you have chain stretch. Basically what youre testing is that the cam and crank are moving together without slop. A stretched chain will allow them to move independant for a couple of degrees as you move through the amount of stretch in the chain. (I think i made sense there)
              Last edited by adventure bob; 01-12-2006, 04:52 PM.

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              • #8
                i don't know how you checked for vacumn leaks or the carb itself, but i'll bet dimes to dollars you missed something. a slipped timing chain will obviously thow the timing off no matter what speed the engine is running. yes, it's got an advance on it, but it will still be off and you would likely have power loss even at high speeds, if not pinging and/or back firing.

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                • #9
                  I'm leaning towards the vacumn leak scenario, too. I had the wandering timing mark, and if I remember correctly, it happened when I had a bad carb-to-manifold gasket. At any rate, it was NOT the timing chain that caused MY problem.

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                  • #10
                    I too think it's more than likely a vacum leak. A slip in the chain causes your timing to be off by the amount of teeth slipped, consistantly. Slipping a tooth won't make the timing change erratically under a light.

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