Brought Dart to shop to fix idling issue and car runs like s**t!

Mopar Performance Issues

  1. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    If the original dist. was in good shape and running good it might be worth a try. Doing a bunch of changes and additions while attempting to diagnose a problem can ADD other problems
     
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    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      Not at at all; but a streeter needs a working vacuum advance.
      The mechanical advance system is only right once, namely after ~3600rpm at WOT.
      You can sorta get close at idle.
      You can get real close from stall to 3600 at WOT.
      But the rest of the time, it is DEAD-wrong.
      So, on a 60 minute cruise around town, how many of those will be at WOT?
      Let's say you are exceptionally brave, and nail it once every 4 minutes for 4 seconds, that comes to a grand total of 1 minute out of 60 , or .0166% of the time. So then 98.33% of the time, your timing is all wrong.
      As an example, when your engine is cold and not on choke, it might want 50* of idle timing. Obviously, you cannot ever give it to her, so you do the best you can, and crank it up to 14*, Now you know why it idles like it does.
      But lets say once it warms up, she is happy with 40; and you still can't meet the need.
      Lets say you put it in gear and give it some throttle ,just enough to tip the V-can all in, and you have modded your Vcan to get 22* out of it. Say you now hit 2000rpm, and the mechanical is delivering .8* per 100rpm beginning at 1000 rpm, Ok lets add it up; initial of 14 + 8* mechanical + 22 in the Vcan comes to 44* and that might just be close.
      So now you continue to accelerate, the throttle is open far enough to accelerate to 60mph at a normal rate, and as you cross 2800rpm, the system is dialing in; 14Idle + 14M + 22V=50, hyup sounds close. But say you hit second gear and want to accelerate a lil more briskly. Just a lil. So now in second the Rs drop to 1700.; so 14 + 6=20 , and say half the Vcan dropped out so 20 + 11=31 perfect. So now you need some giddy-up and are doing 32 mph in second. when you nail it. The trans drops back into first, the Rs climb to ~4200,(with 3.23s), and the timing drops to
      14 + 20 + 0= 34* Badaboom!
      This is just a theoretical curve; your engine will likely want something completely different.
      But now you probably understand the importance of having a working Vcan.
      It is NOT JUST for fuel economy at hiway speed.
      Your three timing systems are constantly working as a team, struggling to create the maximum amount of cylinder pressure and deliver it to the crank, when it in the best possible position ATDC to receive it, and then to send it out to the tires.
      Failing proper timing; you will have to cover the sags and hesitations, with a rich mixture, and pump-shot. And you wonder why your fuel-economy is so lousy? Well there yago.

      But just to be clear;
      I would never advocate going to a points trigger, not that they don't work; I just never would use one on the street. and
      The Vcan does nothing at idle, and nothing at WOT.

      What I would do is get a D with a working Vcan. Even new, they are not that pricey. But Hey, you don't have to get it right away.....
       
      Last edited: Jan 2, 2021
    • LovetheA's

      LovetheA's FABO Gold Member FABO Gold Member

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      Thanks AJ and 67Dart273.
       
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      • volaredon

        volaredon Well-Known Member

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        I never understood why, but when I used to go to alot of car shows and cruise nights, etc where many people have their hoods up for all to see, how many capped off vacuum advance units I saw..... First, vacuum comes from the other end, nothing leaks from the vac advance when it is disconnected, so why does everyone cap the vac advance can? And 2nd, why do so many people not run vac advance?
        The only way this makes sense is on a fixed speed setup like an engine running a pump or an industrial machine or a generator, etc. (Not the capped off advance can, but the limiting of amount of advance)
         
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        • sccachallenger

          sccachallenger Well-Known Member

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          I've had the same experience. I don't know if its cause these people don't put many miles on their cars or what. Is it a point of pride to brag about getting 7 miles per gallon? Not for me!!!
           
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          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            Cuz it's a racecar,don't you know,lol.
            That said;
            There might be a legitimate reason, IDK, to defeat the V-can, but, in a streeter I haven't seen it yet. I suppose that if your engine couldn't produce enough vacuum in the intake, to operate it, in the rpm it needs to work in with your gears; that could be considered a legitimate reason. But IMO, that would not be a very streetable engine. Cuz, even the 292/508 cam in my 367combo, pulled enough vacuum by the time the throttle was opened far enough to activate the port, to pull in all 22 degrees.
            OR
            it might just be that the builder has not yet had time to tune the Vcan.

            But, it could also be; like the tuner kids who put KnN Cone-filters on their fart-canned Cavaliers, but then it doesn't fit in the stock air box, so they just let it suck hot underhood air..... totally defeating the purpose. And nearly everyone of them that I have talked to, swears how much faster their car is now.

            But hey, it could be even worse;
            some of those tuner kids have told me that the filter is worth "x"hp, the fart can is "y"hp, the resistor they Tee'd into the IAT is worth "z"hp, and so on; so in the end they, adding it all together; x+y+z= they doubled their horsepower;
            don't you know.....lol
             
          • mbaird

            mbaird mbaird

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            I think many not running vacuum advance just plain don't know how it works or assume anything with a vacuum hose is emissions related.

            As for those K&N filters on modern cars I have been told the oil can contaminate the mass air flow sensor.
            Makes sense ...
             
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            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Yeah that happened to me on an old 4.0 Explorer . I had to clean it every couple of months, until one day I put some new heads on it..... badaboom. Problem solved.
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              I hate to paint a fellow hot-rodder with the ignorant brush, but yeah...... that does happen.
               
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              • yellow rose

                yellow rose Overnight Sensation FABO Gold Member

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                It depends if you can run the VA or not. The higher the CR ratio relative to the fuel you use, how quickly the mechanical parts can act and react, combustion chamber temp and a bunch of stuff I don’t understand can make it hard to run VA. Even if you hook it to manifold vacuum, it may not pull timing quick enough and it will rattle. If you ease through the throttle it may not rattle.

                I may try VA on my junk, but I have too much crap to sort out before I try it.
                 
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