Unhappy 360 (At idle)

Small Block Mopar Engine

  1. Stephan D

    Stephan D Well-Known Member

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    Hi all!

    My first post at this nice forum after lurking for years.

    I have a stock 1979 360 EH1 with 42.000 miles, one owner
    and complete history, newer rebuilt.

    It has an annoying slight misfire at idle that I have tried
    to track down for a couple of years, without success.

    Pulls fine and has no misfire as soon as it leaves the
    idle state.

    Facts:

    Newly rebuilt original Thermoquad
    Mopar stock electronic ignition
    New spark plug wires
    Timing 15 degrees initial without vacuum
    Softer springs in distributor according to previous owner
    Full vacuum advance
    727 transmission
    Maximum 18" vacuum in neutral and 16" in gear
    Vacuum fluctuating with the slight misfires

    Tried troubleshooting:

    Pulled plug-wires one by one, all seems to be working
    Adjusted idle-mixture for best vacuum

    Here is a video of the engine at idle,
    first in neutral and then in gear:

    Now I have run out of ideas, any help is welcome!
     
  2. BigBlockMopar

    BigBlockMopar BigBlockMember

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    Welcome.
    Clamp the rubber PCV-line closed when idling as a test.
    Idle speed will most likely drop and get a bit steadier.

    Could be the PCV is causing a slight lean condition that causes an occassional misfire.
     
  3. Tooljunkie

    Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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    Pcv isnt right. i see vapours coming out of the vent hose that connects to air cleaner.
     
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    • Stephan D

      Stephan D Well-Known Member

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      Thanks for quick replies!

      I had the vacuum gauge attached to the PCV hose, so no PCV functioning when I took the video.

      PCV valve is new as well.

      I have tried spraying brake-cleaner around the intake and carb base with NO change in idle speed.

      Keep the suggestions coming :)
       
    • Tooljunkie

      Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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      Pcv is a calibrated leak. By putting the gauge on that port you have changed the afr.
      Use the brake booster port or a port on intake manifold.
       
    • Stephan D

      Stephan D Well-Known Member

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      It has those small misfires when everything is connected the right way and no vacuum gauge is attached.

      I will connect gauge to the brake booster next time.

      EGR valve and cats are long gone.

      Just i small squirt of brake-cleaner down the carb kills the engine immediately.
       
    • halifaxhops

      halifaxhops It's going to get stupid around here! FABO Gold Member

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      Know anyone with a scope to eliminate the ignition side?
       
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      • Stephan D

        Stephan D Well-Known Member

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        No not really, going to the workshop next week for new valve seals, not sure if they have a oscilloscope.

        I have an ancient ignition timing gun.
         
      • Mopar73340

        Mopar73340 Well-Known Member

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        If it has all the vacuum connections on the “tree” feeding cylinder #8 try plugging them. I have found in the past #8 tends to run lean which will cause a slight miss feeling at idle.
         
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        • Stephan D

          Stephan D Well-Known Member

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          Just checked the vacuum tree, and there are only distributor and brake booster attached there, both with new hoses.

          On the back of the carb is a hose (old) connected to the "ECS canister", disconnected that one and put my finger in the tube on the carb, made no diffrerence.
           
        • Mopar73340

          Mopar73340 Well-Known Member

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          Distributor should be connected to ported vacuum on the carburetor. What is the timing set to at idle? Your getting full advance if connected there. I would still plug the brake booster and test also.

          (The above is true with the emissions crap bypassed)
           
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          • MOPAROFFICIAL

            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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            A good motor doesnt have that amount of blow by.

            Thing needs to be gone through.
            Pcv looks new.
            Noisy in the video, cracked ring sounding..chattery
            Cracked or seeping gasket between cylinders is a common one too... puts lil heat spider cracked in the head when the combustion passes into the next cyl.

            BUT.. to not jump head first into the more obvious issues shown by the blow by... try a spray bottle of water, mist around the carb and are if it cleans up a bit.
            Those tiny primaries seem to make a lot of vac noise in the vid, a lot, so you may have a vac leak.
             
          • TrailBeast

            TrailBeast AKA Mopars4us on Youtube

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            I thought the same thing when I saw that amount of case venting.
             
          • 318willrun

            318willrun Utube channel 318willrun

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            Wonder what the temp is in Sweden....?? Could it be cool temps exaggerating the venting ?
             
          • TrailBeast

            TrailBeast AKA Mopars4us on Youtube

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            It's not what the wind is blowing, but that the wind is blowing.:D
            That's a lot puffing IMO, no matter what it is coming out the hose.
             
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            • Stephan D

              Stephan D Well-Known Member

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              Temperatures in the morning was below freezing when i filmed this, smoke out the exhaust pipes as well, normal at this temperature I would say.

              The ugly noise in the video is from a metal tube that goes from the exhaust manifold, connected to the air filter box with a rubber hose when it´s in place, som sort of remains of the pollution stuff I think.

              When everything is in place I would say the there are no exceptional sounds from the engine anymore, but with this tube open, I must wear earbuds...

              Keep em coming... :)
               
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              In neutral or drive can make a difference.
              Turn the screws a little richer (no more than 1/4 turn, start with 1/16 or 1/8) which should be closer to what it wants with a load on the engine. That's a pretty standard procedure when setting toward the lean side. Go lean until miss or rpm drops (or vac drops) and then back out 1/8 or 1/4 turn.
               
            • Stephan D

              Stephan D Well-Known Member

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              Should idle mixture be set in Neutral or Drive?

              Richer = counter clockwise?

              For now I just set the idle screws 1,5 turns counter clockwise from full in, it seemed to give the best result.

              Tomorrow I will disconnect the brake booster, plug it and see what happens, and do some filming of the engine running with everything attached.

              My BMW-employed neighbour says "it's American - they newer where any better than this",
              I would very much like to prove he is wrong! :)
               
            • MOPAROFFICIAL

              MOPAROFFICIAL FABO Gold Member FABO Gold Member

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              Ask him why BMW's dropped their v8's from the 60's all together, I'll save you the time... because they were shit, just like volvos early v8...shit...
              now the inlines...great, most of them.
               
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              For the mix I get it close in neutral, turn richer and then check results in drive. That way I'm behind the wheel and can put foot on the brake.

              On later vehicles, if stock, sometime the sticker under the hood says set the idle rpm in Drive. In which case I'll do that the same way.

              On a normal carb, yes, counterclockwise is richer.
              When turning the screw leaner, the difference between running well and running poorly happens pretty quickly.
              When turning the screw richer from best efficiency the reduction in performance is harder to detect.
              So its easier to set the idle mix by working toward lean and then backing off.

              Side note: Concern about hydrocarbon and CO emissions resulted in manufacturers specifiying slightly lean idle mixtures. This began in the mid 1960s.
              I don't know about your particular carb. But many of the carbs used late 60s into the early 70s only allowed for very fine idle mix adjusments. They did this by various means. It's possible your carb's idle screws do not allow as much range of adjustment to the idle fuel-air mixture.

              Use ported vacuum since you have 15 degrees at idle. Idle sounded like its in the 600 -700 rpm range. yes?
              It's not surprising your engine likes lean mixture in neutral. This is because of the there's no load and there's vacuum advance providing really long lead time. When you ask the engine to work (place in gear) at idle speeds, a bit richer will stronger. Richer mixtures also burn faster. Lighting them off too early wastes energy.


              Most earlier emissions era distributors already had very soft springs in them.
              They also had long advances.
              1979 I don't know.
              You can and should explore this later.
               
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              • Phreakish

                Phreakish Well-Known Member

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                Can you take a picture of that? Do you have an air pump (smog pump)?

                I'd also be looking at the egr valve. If it's open when it shouldn't be, it can cause trouble.
                 
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                • PRH

                  PRH Well-Known Member

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                  First thing I’d do is move the vac advance hose to the ported vacuum port on the carb(there should be no vacuum there at idle).

                  Then reset the idle speed......... then adjust mixture screws to achieve highest vacuum.
                   
                  Last edited: Mar 30, 2020
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                  • Stephan D

                    Stephan D Well-Known Member

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                    Sorry for late feedback, a Blizzard and a trip to the workshop(other issues) has got inbetween.

                    Anyway, this time i set the inital timing to 10 degrees at idle, it obviously was close to 0 before, connected vacuum-meter to the brake-booster hose, not the PVC-hose that I used before.

                    After som fiddling with the timing and adjusting the idle-mixture screws, I think I found an acceptable sweet-spot where it idles quite smooth, runs well in traffic and no kickback att all on cranking, and no audible pinging.

                    Please have a look, listen and your thoughts:
                     
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                    • Stephan D

                      Stephan D Well-Known Member

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                      And the tube with the ugly noisy sound, I think it´s some sort of airpump for the long gone cats, I could live without it:

                      [​IMG]
                       
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      Yes. That looks like a check valve for an air injection system. It connects to the exhaust. If there is no pump then agree, take it off and be sure the exhaust is plugged (or get the pump). Usually used to help react with remaining hydrocarbons and to raise the operating temperature of catalytic converters. 1978 had no cats, 79 probably did.

                      PS. Try to seperate the spark plug wires more if you can. it can reduce cross talk.
                       
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