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Low Rpm Knock/ping

Discussion in 'Early CJ5 and CJ6 Tech' started by erhuff, Jul 10, 2017.

  1. Jul 10, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Dec 16, 2011
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    190
    Hey all,

    I am hoping someone has a good ear and can take a listen to this. I noticed it yesterday when I had to slow down on a 15% incline in third, then got back on the gas without downshifting. I tested it out and I can only hear the pinging if I am on the throttle at lower RPMs. If I downshift, it seems to go away (or the exhaust volume is too loud to hear it). I get nothing at idle or cruising speed.

    [​IMG]

    If that embedded video doesn't work, here is a link to the video on Flickr:

    VID_20170709_173822497

    Some background on the motor and jeep:

    I rebuilt it in 2002, and it ran for a few years every now and then, then sat for a few more, and now I am running it about 200-500 miles each year. (hopefully more now that I have finished all the projects I wanted to do)

    I put a professionally rebuilt carb on it 3 years ago and it ran rich until last week when I had my shop where I get my sticker adjust the air/fuel mixture for me. They said it was really dirty so when they cleaned it the idle was really high. Now it runs nice and smooth and doesn't smell like it is running rich.

    I just put a full tank of 87 in and the gas that was left over in the tank had Sta-bil in it since I don't drive it enough to go through full tanks of gas that often and that gas is a several months old since I was finished the roll cage and couldn't drive it during the spring.

    Any help would be much appreciated. Thanks!
     
  2. Jul 10, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Dec 16, 2011
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    190
    After a bit of research, I am assuming that I am getting detonation or pre-ignition. I am going to try out two things to start:

    1. Higher Octane Fuel
    2. Adjust the carb to run more rich

    If that doesn't work, I will check the timing or may look at a Sea Foam Green or similar product. My hope is that it is just running lean after being adjusted the other week.
     
  3. Jul 10, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    Why wouldn't you check the timing first? It's a pretty basic and important spec, and necessary for any routine tune-up.

    What engine are we talking about?
     
  4. Jul 11, 2017
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    Good call. My thoughts go to spark side as well. Check timing, plugs and ohm spec on coil/wires.
     
  5. Jul 11, 2017
    erhuff

    erhuff Western MA

    Western MA
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    I didn't do the timing before, so it isn't something I am familiar with, but I will do that. It is a 225 motor. I was going to make a trip to Advanced today, so I will pick up a timing light since they don't seem too expensive to bother renting.

    When I talked with the garage that did the tune he said he only adjusted the idle mixture and not the jets, so it should be what he did and to check the timing and that I have the right plugs for the heat range. What plugs do you all use? I am going to replace the plugs I have Champion RJ12YC.

    Thank you both for the input and help. After a bit of research on what detonation and preignition can do, it has me a little cautious.
     
    Last edited: Jul 11, 2017
  6. Jul 11, 2017
    colojeepguy

    colojeepguy Colorado Springs

    At the foot of...
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    The idle mixture (and idle speed) are the only external adjustments on the carb.
    Your problem really sounds to me like timing is too far advanced.
     
  7. Jul 11, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Dec 16, 2011
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    Thanks for the input! I will get a timing light and check that. Forgive my ignorance, but as the timing chain wears in/stretches, will that mean the timing will essentially advance during that process? Just trying to learn the entire process and mechanics behind it.

    I ended up pulling a few plugs to check them and a couple of them were really torqued down, so I slipped and snapped one. I guess I will put on new plugs while I am at it too. Here is an image of the plugs. They look pretty good and don't show any signs of detonation or preignition, which is great.

    [​IMG]

    Thanks all for the feedback and help. It is appreciated!
     
  8. Jul 11, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    Those insulators look a little bit toward the 'hot/lean/advanced" side of the spectrum to me. Consistent with 'pinging.'
     
  9. Jul 11, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Thanks. Should I hold off on buying all 6 plugs and just replace the broken plug while I adjust the timing then check again to see if I need colder plugs?
     
  10. Jul 11, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Why would you? Assuming they are the right plugs, they are the symptom, not the cause.

    Start with a basic tune-up to factory specs. Anything else is chasing your tail until you do that.
     
  11. Jul 11, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Will do. Makes sense.

    Thanks.
     
  12. Jul 11, 2017
    ronnie victor

    ronnie victor Member

    raleigh, nc
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    Before timing, remember to paint a white line in the notch of the timing pulley wheel so that you see the notch under the timing light strobe. A bottle of white-out from the Dollar store will suffice (has a tiny, thin application brush inside). Be aware of the fan blade too (safety)
     
  13. Jul 11, 2017
    erhuff

    erhuff Western MA

    Western MA
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    Thanks, was just reading the chilton's manual i have and they mentioned painting it white. I was going to use a silver sharpie, but white out is pretty ingenious. I will do that instead.
     
  14. Jul 11, 2017
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    White nail polish works really well.
     
  15. Jul 14, 2017
    erhuff

    erhuff Western MA

    Western MA
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    So I was able to check the timing with the new light. It was around 15 degrees out. I brought it down to 5 degrees and the engine slowed down to a nice purr. One thing I noticed was every 4-5 flashes the degree reading would jump 1-2 degrees or so, then go back to the original reading for another 4-5 flashes, jump, come back down, and so on. Is that normal? I set it on the lower more constant reading.

    Hope that makes sense and thanks for the help.
     
  16. Jul 14, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Looking at your plug gap you must be using the standard dist. (point type) Have you checked the dwell? How much wear do you have in the advance weights?
     
  17. Jul 15, 2017
    erhuff

    erhuff Western MA

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    Not sure on the advance weights. I do know it has vacuum advance, so would it also have advance weights? (I did unplug the vacuum line to the carb)

    I did not check the dwell, but will do that next. Probably Sunday.
     
  18. Jul 15, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Timing can't be set accurately unless the dwell is correct first.
     
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  19. Jul 15, 2017
    erhuff

    erhuff Western MA

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    Got it. I will try to do that next.

    If we assume it was set properly before, can that change over time?
     
  20. Jul 15, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Certainly. Points routinely wear, and distributor bearings need to be good, etc.
     
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