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Popping noise at idle

Discussion in 'CJ' started by Jaycool47, Jan 27, 2022.

  1. Jan 27, 2022 at 4:46 PM
    #1
    Jaycool47

    Jaycool47 [OP] New Member

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    I have a 83 cj7 with a 4.2. It has a popping noise at idle, the only way I can get it to stop is pull the #6 plug wire and it doesn't sound like it's missing but the popping stops. The compression on #6 is 150. I have spark and a new plug so I'm not sure what's going on. Anyone have any ideas? Thanks in advance.
     
  2. Feb 1, 2022 at 11:28 PM
    #2
    Groundfault

    Groundfault Well-Known Member

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    5.7 V8 with Whipple Supercharger, TH350 w/B&M Shifter, NP205 TC, Dana 60 front 4.56, GM 14 bolt 10.5 rear 4.56, 4 wheel discs, Bilstein shocks, 6" lift on 37's, Autometer gauges, all led lighting and a few other things.
    Any other symptoms? Is the noise always there, even when the engine is hot or just after cold start up? Any power loss or rough running? Plug wires in good shape?
    150 compression is good so it seems unlikely that you're exhaust valve is burnt or not seating.
    Could just be a small exhaust manifold gasket leak at #6. Might try spraying soapy water on it when engine's cold and see if it blows any bubbles.
     
    aggrex likes this.
  3. Feb 2, 2022 at 7:54 AM
    #3
    Jaycool47

    Jaycool47 [OP] New Member

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    I don't hear the popping noise while I'm going down the road, just at idle hot or cold. I've messed with the timing a little and didn't seem to change any. I have discovered that my timing chain is really lose so I'm thinking that might be it. But why just the one cylinder?
     
  4. Feb 2, 2022 at 6:14 PM
    #4
    Groundfault

    Groundfault Well-Known Member

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    Timing issue would cause missing and backfires on all cylinders.
    Air filter and clogged fuel filter can cause lean or rich condition and popping, once again on all cylinders.
    Possible for a bad spark to cause incomplete detonation in one cylinder. Make sure your plugs gapped right, plug wire is good, check distributor cap for signs of arcing.
    Head gasket leak to outside of cylinder will cause a popping noise, but I doubt you'd have 150 compression reading.
    A blown or cracked exhaust manifold gasket on #6 would cause popping sound and would all but disappear without cylinder detonation on #6.
    I don't know how loud the popping is. Is it really going away at higher rpm or just can't be heard over the road and wind noise. Try slowly opening the throttle manually at the carb to increase rpm while parked and see if it goes away.
    Best of luck. Hope you find cause.
     
  5. Feb 2, 2022 at 6:30 PM
    #5
    Jaycool47

    Jaycool47 [OP] New Member

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    Thank you sir I will definitely check those things out, appreciate the help.
     
  6. Mar 6, 2022 at 8:41 AM
    #6
    MTgeezer

    MTgeezer Well-Known Member

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    The AMC 258 is know for exhaust manifold leaks. The first thing I would be checking is the gasket at #6. As above, soapy water when cold.
     
  7. Nov 9, 2022 at 10:27 PM
    #7
    caltexjeeps0436

    caltexjeeps0436 New Member

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    ground up restoration and mods to compensate for my oscar meyer weiner
    Sticking intake valve can cause it if its popping through carb! ask me how i know! :bananadead:
     
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