383 Cruising Issue

Discussion in 'Mopar Performance Issues' started by 6kevin8, Aug 28, 2018.

  1. 6kevin8

    6kevin8 Well-Known Member

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    I'm having an issue when cruising in my dart for somewhat long trips on the freeway. When I go over 20 miles or so, if I try to push the car it'll start to backfire and act like its not getting fuel. It makes this noise like "k-thunk, k-thunk, k-thunk, k-thunk" until I let off the throttle.
    The car has a pretty stock 383 with schumacher headers. The 727 has a 2200 stall. I was in an accident recently so I don't have a full exhaust system... it's cut off right after the mufflers. I don't remember having this issue prior to my accident, but there are some changes that the car has had since. The rear end now has 3.23s and a true trac instead of 2.94s. I'm also running 27" tall wheels in the back now. When I'm on the freeway, I'm usually cruising at 4000 rpm give or take. Also, my car before didn't have a hoodscoop. Quite a few new variables, but any thoughts?

    Dart.jpg
     
  2. AJ/FormS

    AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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    The math says; 4000~94 mph with 3.23s and 27s. That sound right?

    My guesses:Overheated sparkplugs due to;
    A)wrong heatrange ...... Move colder 2 heatranges and/or
    B) lean running,..............Fatten up the main jets 2 sizes and make sure the fuel level is and remains correct,and/or
    C) insufficient timing........Make sure the Vcan is functioning,and the total timing is near 55*@4000@cruise.
    D) engine running hot.
    then roadtest.
     
    Last edited: Aug 28, 2018
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    • Murray

      Murray FABO Gold Member FABO Gold Member

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      Or can the carb be starving? Low float level, clogged fuel filter or gas tank filter?
       
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      • 6kevin8

        6kevin8 Well-Known Member

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        I'm not cruising say 94, I'm thinking the shop who did my rear end might've put 3.55s in it.
         
      • 6kevin8

        6kevin8 Well-Known Member

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        I do wonder about starving. The carb is a 600 cfm Holley but I mean, these things used to come as 2 barrels right?
         
      • 6kevin8

        6kevin8 Well-Known Member

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        We're going to check how accurate the tach is too.
         
      • My70b

        My70b Well-Known Member

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        Happened to my daugthers dart coming back from Carlisle the triangular plug on the orange box kept coming loose fixed that and perfect

        dart1.jpg
         
      • 6kevin8

        6kevin8 Well-Known Member

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        what triangular plug and orange box?
         
      • AJ/FormS

        AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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        Holy smoke that looks very similar to my first Dodge, a 70Swinger. Beautiful car
         
      • AJ/FormS

        AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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        That's probably a good idea cuz 3.55s and 27s comes to ~86@4000,
        65 should be about 3000.
         
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        • 6kevin8

          6kevin8 Well-Known Member

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          My dad is the wizard when it comes to these cars, but just to hear opinions... is 4000 rpm too high for cruising when it comes to these engines?
           
        • Alaskan_TA

          Alaskan_TA Well-Known Member

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          The aftermarket fuel pump push rods are notorious for wearing out, so you can check that.
           
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          • AJ/FormS

            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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            I wouldn't cruise there because;
            A) that's a lot of wear and tear on the engine About 70% more.
            B) NVH. Noise,Vibration and Harshness.
            4000 at 65 is friggen loud. And
            C) the driveshaft is whipping around something fierce.
            D) the rear end is running a lot warmer, and is gonna want a better oil.
            E) the automatic is gonna run warmer too..... and it puts it's heat right into the coldest part of the rad...... which then immediately goes into your engine. So your cooling system has to be up to the task.
            F) RPM Sucks gas.
             
            Last edited: Aug 29, 2018
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            • 6kevin8

              6kevin8 Well-Known Member

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              All makes sense to me. I'll just cruise with it at 3000 +/- especially since I don't have a dedicated trans cooler. I also want this engine to last me for a few more years at least lol.
               
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              If its backfiring in the exhaust then there is unburned fuel there, plus enough heat to ignite it of course.
              Running out of fuel it sometime coughs and then dies.
              Take out a few spark plugs and see what they have to show.
               
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              • 6kevin8

                6kevin8 Well-Known Member

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                I don't think it was backfiring, and the tank probably had 15 gallons in it when this occurred. The spark plugs are practically new.