Engine still not right after timing set

Big Block A body Tech

  1. phaelax

    phaelax Well-Known Member

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    I'm not the expert, so bear with me. '73 Duster with a '78 (i believe) 440. Quickfuel 750 (vacuum secondaries if I remember correctly) electronic choke.

    The timing was off, that was apparent. Bolt on the distributor came loose one day. I've had two people help me try to set the timing but it never quite sat right. I took it to a local shop today to figure out what's going on. After replacing the plugs and setting the time, the guy says he has it started and running but something is still off. I forget exactly what he said but says it might be a valve partially sticking open and would have to take off the headers and possible pull the motor partially out to test compression. He was asking me for the cam card, which I thought was in the car. All I can remember is it was a comp cam, possibly with .4xx lift. I know I have paperwork for the cam that was put in years ago but I'm in the process of moving and it could be boxed up.

    I know all this info is rather vague, but what else could cause the engine that has proper timing set but still feels otherwise? Either way I feel like this little tuneup is gonna end up costing me more than expected.
     
  2. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    Do you have to do that to change the plugs?

    If not, no reason to do all that to check the compression.
     
  3. MOPAROFFICIAL

    MOPAROFFICIAL FABO Gold Member FABO Gold Member

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    Pull the cover and rockers, see if one is lower than the rest.
    If it was hung open, you would get a random pop out the tail pipe from un burnt fuel igniting in the exh tract.
     
  4. Jim Lusk

    Jim Lusk Well-Known Member

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    Went through that with a 340 recently. Should be able to get the plugs out without pulling the headers. Run a compression test, leakdown on the low cylinders if there are any. We had two bent exhaust valves that showed up nicely on the leakdown. They weren't bent by much and the engine ran ok, just couldn't get it to burn clean or at the timing I wanted. Also turns out it had a .509 or similar cam. We replaced that, as well...
     
  5. slickchick

    slickchick pedal cars only

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    Or . . . . if the balancer slipped ,causing inaccurate timing set ??
     
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    • 66fyssh

      66fyssh Don't Stop Believin' FABO Gold Member

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      Was it running well before the distributor hold down bolt came loose?
       
    • fklskv

      fklskv Well-Known Member

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      You have to get creative to do a compression check on a 440 with headers. Most of the work is done from underneath.
       
    • phaelax

      phaelax Well-Known Member

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      Like a misfire? Cause I was getting that kind of noise, just figured it was from the timing being off.

      Yes.

      As for removing the headers, it wasn't to change the plugs but to attach the machine to check pressure he said.
       
    • Jim Lusk

      Jim Lusk Well-Known Member

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      As stated it can probably be done from underneath without removing the headers. Post some pics of the headers.
       
    • phaelax

      phaelax Well-Known Member

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      Schumacher tri-y headers if I recall correctly. I can't get pics at the moment, the shop is an hour from where I currently live (downside of living in a cornfield).
       
    • oldkimmer

      oldkimmer FABO Gold Member FABO Gold Member

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      Ur mechanic obviously hasn’t worked on many Mopars if he thinks that’s a hard job. Kim
       
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      • phaelax

        phaelax Well-Known Member

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        He said it had something to do with attaching the machine and not having room with the headers. But it doesn't look like its necessary as it appears to be a voltage issue. Says he got the car to run pretty well at first then it starts having issues after driving it. He measured around 3-4 volts (i assume with engine running) at the coil and said it was very hot. After letting it cool off, it ran ok again. He wants to replace it with an msd ignition system; ditching the ballast and mopar ecu altogether but keeping the existing distributor.

        The good news is, he pulled off the carb and checked that out and said it was clean and everything on it was good. So at least one thing I've done myself was correct.
         
      • threewood

        threewood Well-Known Member

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        How did your guy set the timing? Did he also set mechanical timing? Check total timing?
         
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        I don't think your "mechanic" knows what he is talking about

        If he really did measure 3-4V that is LOW and either is loaded down by too much current---which might indicate a shorted coil------or too low because the supply to the ballast is low. That might indicate a wiring problem in the harness, AKA bulkhead connector, ignition switch, etc.
         
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        • AJ/FormS

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

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          A sticky valve will show up several other ways, besides a leakdown, namely ;
          >If an intake;
          At the end of the intake stroke, the piston may may push a lot of it's just-inducted A/F charge back up into the intake manifold, and on an undamped vacuum gauge you will see the pressure pulse . When the spark hits, I suppose, at low rpm, that fire may get up into the intake.Generally, as you rev it up, the misfires have a tendency to go away and the engine smooths out. Also, at low rpm, if you whack the throttle open, she will likely send fire thru the carb.

          >If an exhaust valve;
          during the power-stroke;
          it will send fire into the headers. In shortys, it is possible for that fire to ignite unburned fuel exiting adjacent cylinders. The result is some popping in the pipes.
          >on the intake stroke;
          The pressure in the intake may be higher compared to what is in the headerpipe of the bad cylinder. So when the piston goes down on the intake stroke, the cylinder will tend to pull in exhaust, and so, not enough fresh A/F charge. It is possible for that cylinder to misfire, sending a portion or all of that charge into the header, where it can be ignited by fire from another cylinder. And, the exhaust is gonna both pop, and stink.

          >Many times if you slow the engine right down,you can feel the piston intermittently sucking at the end of the tailpipe. If you have a cross-over, you will have to plug one of the pipes.
          >>Not valve related;
          If your headers are not properly sealed at the heads, then they will pull fresh air in, as part of the way they operate. Any unburned fuel in the headers is gonna "explode". This makes a lotta noise in the headers, and COULD make it seem like the engine is not running right. This is worst at low rpm/idle.
           
          Last edited: Sep 24, 2020
        • phaelax

          phaelax Well-Known Member

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          I appreciate all the detailed feedback. I spoke to my mechanic today and he's waiting on some new plug wires. Apparently, only 4 of them were working correctly he said. Considering I just replaced those wires 2 years ago I'll have to note what brand they were from Jegs so I never buy them again, because that's pretty terrible.

          The pops/misfires I'd hear were more prevalent when the engine was under some load.

          Once all the wiring is taken care of, if there's further issues I'll definitely bring all this up with him to check out. He seems like a pretty reasonable guy and has been straight forward about what actions he is doing.
           
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