popping from exhaust on deceleration

Electrical & Ignition

  1. Bill Monk

    Bill Monk Well-Known Member

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    First, let me say I appreciate everybody that has taken the time to give advise to me on this site. It has proven to be an invaluable tool to diagnose problems so thanks!

    Now to the problem: Engine has a slight hesitation at low throttle but runs like a scalded dog when you step on it. When I take my foot off the throttle, there is a random popping from the exhaust. It isn't a loud bang but a pop pop and it is random. It doesn't seem to do it when decelerating from a light load.
    I'm pretty sure it is not a vacuum leak and the car has new plugs. One thing I noticed when trying to get it timed in is that the vacuum advance on the distributor does not appear to be working. I have it plugged to manifold vacuum and I saw no change with it plugged off v/s plugged in. I rather doubt that has anything to do with the popping but just throwing that out there. Does this sound like a timing thing or what?
     
    Last edited: Apr 21, 2017 at 6:00 AM
  2. the mississippi madman

    the mississippi madman Well-Known Member

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  3. miller

    miller Well-Known Member

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    A quick way to check if the distributor advance is working, pull the cap, and see if the rotor will move in one direction a little, then move back into place.
    Doesn't matter what kind of distributor, the advance 'plate', that the points mount to, rotates a number of degrees. That's how the advance works. Does it move?
    If not...could be a couple things, though the usual problem is it's dry, and hung up. If you pull the rotor itself, look at the top of the shaft, where it fits. Should be a small felt 'oiler' just inside the top of the shaft. The main shaft on the distributor, is a smaller diameter, at the top, with part of the advance plate that fits onto that smaller end. Needs to be able to rotate, and spring back into place.
    The oiler felt should get 'serviced' now, and then, by putting a few drops of oil on it. Let the oil soak in, then wipe off the excess. Oil in it, works it's way to the space on the shaft, that rotates...lubing it. If it goes dry, yeah, can rust and lock down.
    Worst case, is you have to tear down the distributor, to get in there, clean it up, to get it to work.
     
  4. Bill Monk

    Bill Monk Well-Known Member

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    I'll check it out but I don't think that's the culprit. I have mechanical advance at higher rpms.
     
  5. moes

    moes Well-Known Member

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    do you have a free flowing exhaust? Any time the exhaust is “opened up” the condition of deceleration pops is much more noticeable and problematic. An open exhaust allows additional air to be “sucked up the pipe” during closed throttle and any unburned fuels, then ignite and “snap/crackle/pop”
     
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    • khryslerkid

      khryslerkid FBBO Gold Member FBBO Gold Member

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      I'll agree to the open exhaust and I believe there is more oxygen in the system than in a conventional factory setup.

      I removed the inside honey comb from a catalyst converter once. It was breaking up and clogging the pipe. It had to have one on there for inspections so I just gutted it out and reinstalled. That was a mistake, it would build up unburnt fuel and backfire like a 12 guage shotgun on deceleration!
       
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      • Bill Monk

        Bill Monk Well-Known Member

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        Stock manifolds, 2 1/4" pipes with a crossover through hemi mufflers.
         
      • Fran Blacker

        Fran Blacker Well-Known Member

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        If you want to test the diaphragm put a hose and "suck" through it and stick your tongue over the hole if it doesn't hold a vacuum it's bad. You maybe able to see plate move with cap off.
         
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        • Ranger16

          Ranger16 Well-Known Member

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          That does sound a lot like what you see on NASCAR races.
           
        • RJRENTON

          RJRENTON Well-Known Member

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          Depending on the year of the car and if it has any of the original emission control equipment, some cars (usually a manual trans) engine transmission combinations had a deceleration control device that advanced the vacuum to the distributor. Later models had a Electric retard system as part of the distributor 's vacuum advance that retarded the spark at closed throttle to prevent an over rich condition and "popping" in the exhaust.
          The other contributors suggestions should be considered. Will or is the popping exhaust harmful? Possibly. Check the condition of the spark plugs to see if the engine is too lean. It sounds like you may have a vacuum leak causing an off idle stumble.
          Bob Renton