Help with a miss and voltage drop

Slant 6 Engines

  1. gdizzle

    gdizzle Well-Known Member

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    66 dart 225. converted to HEI, NOS dual field alt, NOS recurved Elec distributor, new NGK plugs, new Wires, new Cap, new Rotor. Recently Lashed, Super Six setup with Carter BBD which has been rebuilt. Timed to 18 BTDC, (with vac plugged).
    Curb idle at 850. Drops to 625 when put in gear.

    Ok so I am getting a sporadic miss when I am in gear, stopped at a light. I have a volt meter installed in the dash (digital) and it shows a 1 volt drop when I hear the miss happen. It is a very quick miss/drop. Like it will hover around 14.3, then all of a sudden drop to 13 when the miss occurs. Also when I say Miss, I mean does not fire. I do not mean a backfire.

    If I put the car into neutral rpms go up to 825 and there is no missing.

    So why do I see a voltage drop when the miss happens? Can this be caused from a bad eCoil?The eCoil is used from junkyard. Could it be caused from the HEI Module? Any ideas what to troubleshoot? thanks for any help.
     
  2. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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  3. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    Yep, it could be either.
    I would sooner suspect the module than the coil, but it's possible.
     
  4. nm9stheham

    nm9stheham Well-Known Member

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    I would also look at the ignition circuit into the engine bay. If you kept a lot of the wiring, then it is feeding both the ignition and the alternator/regulator. The ignition connection dropping out for a moment would cause both problems that you describe. (Why that would happen only at idle and in gear, I cannot say but stranger things have happened.)
     
  5. cdnEHbody

    cdnEHbody Well-Known Member

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    Are you using good quality caps and rotors? Always buy nos made in usa
     
  6. gdizzle

    gdizzle Well-Known Member

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    Great ideas. Keep em coming. When I switched to HEI, put ignition on relay. I think all my wiring is new. Also have relay on the HEI. Also done the MAD bypass. Cap and Rotor are the Blue Streak stuff. All good.
    I just tried a new eCoil, and it made no difference. I can now try a new ICM, but of course I don't have any Thermal paste laying around, so Had to order some.
     
  7. Killer6

    Killer6 Well-Known Member

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    Well, You haven't blown any fuses or fusible links yet, but it could be an intermittent short in the alternator. That happened to My Pop's '86 Horizon, it blew a link on His way
    home from work, He got it rigged w/an inline fuse but would pop out of the blue. The car would shut down immediately, so I followed and We hot wired it and it sailed home.
    After some lengthy checking it reared up it's ugly head, one of the wires came loose and exposed in the rotor, it would ground to the rotor body just for an instant.....but
    that's all it took. The car was maybe 3 1/2 yrs. old & maybe 50K mi. or so..............just a thought if nothing obvious turns up................................
     
  8. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    "Some things" I would do. If your voltmeter is routed into the engine bay, temporarily rig it so you can monitor various different points. Probably the first would be the IGN1 (ignition run) wire right near where it comes out of the firewall into the engine bay.

    Another thing to try is to run the car a short ways (daytime) with the voltage regulator unplugged. This will eliminate the alternator as a source, and if you are losing battery power it might show that up. Try to drive on low traffic, county, etc roads.

    With the engine idling, go around and wiggle the livin' 'ell out of a few things.........the harness where it approaches the alternator, the bulkhead connector, and around the distributor/ ignition. Also around the starter relay. See if you can duplicate the problem
     
  9. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    the 850/650/18*timing, idle throws up a redflag to me.
    I'll just bet you the transfers are nearly closed and you're probably idling on the mixture screws alone.Too much idle-timing will do that. It's not too much for the engine, but rather too much for the carb.Fix that first then maybe it faith-heals.I would target an idle speed of about 550 in gear, even less, if the compression is good.
    I would expect the TC to drag the idle down only 50 to 100 rpm.

    Most ignition systems will be fine down to 10 or 11 volts.
    Look for an A/C component coming out of the alt.
     
  10. gdizzle

    gdizzle Well-Known Member

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    The reason I have the curb idle so high is to help keep the headlights from strobing at stop signs. But I am going to try to retime it again, and then adjust the carb. and then replace the ICM. My main confusion is trying to understand why when I hear the miss, I see a big voltage drop (1v). Is it cause and effect?? is it dropping the voltage because it missed? Or is is missing because the voltage dropped?
     
  11. cdnEHbody

    cdnEHbody Well-Known Member

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    I had a problem with my car doing that. The igition coil was arcing from the high side to the 12v side. My old plug wire set had allowed one ot two of the rubber boots to be pushed down on the plug porcelain but the actual metal that grips the plug was not touching. So it would jump that gap internally but once in a while it wouldnt and the high output coil voltage would find a spot that was easier...and it was right at the coil. Tfi setup and highoutput accel coil. Hot spark!
     
  12. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    Kudus to you for finding that, many guys have missed it.
    That big bad sq-top Yellow is the best coil I ever bought. It does everything it's supposed to and more, and mine is close to 15 years old or more.In the Big picture, it was the cheapest coil per mile driven, ever.
     
  13. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    Just so you know, with the ignition only operating, I have driven about a 100 miles on battery alone, and then I reached my destination so who knows how much further she would have motored. Del had/has a good idea.
    Have you checked for an A/C component yet?
     
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    • gdizzle

      gdizzle Well-Known Member

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      Forgive me but what is A/C component? I dont have AC. Also i just swapped in brand new ICM and eCoil. Reset idle and timing and mixture. It is still doing random misses, and with idle
      Now around 550, that miss almost feels like it wants to stall. What can i trouble shoot now? Wires are 6 months old Denso 7mm. Plugs are 6 months old NGK . I have put less than 300 miles on these....
       
    • cdnEHbody

      cdnEHbody Well-Known Member

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      No errant spark flashes under the hood? Run it when dark and peak under
       
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      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        On a side note these kinds of problems are almost ALWAYS caused by something like a wire opening up......it allows the spark voltage to climb, and just like lightning........it looks for the easiest path to ground. Internally broken plugs can do this as well
         
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        • AJ/FormS

          AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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          A/C equals alternating current.
          Your alternator produces alternating current; the same type of electricity that runs almost everything in your house.
          But in order for your car to be safe, this alternating current has to be changed into DC,aka Direct Current. The device that does this is usually built in to the alternator, and is called a diode. There are usually 6 of them and they are very robust devices. But occasionally they fail, usually only one, or one atta time. And then A/C, or alternating current leaks into the DC system. Of course most of the wiring on your car is not designed to operate on AC, so chit happens. It just so happens that electronics are the most sensitive to this chit.
          The lights don't care, unless the AC is too high or lasts too long. Same with the battery, or even the starter.
          But not anything electronic, from the radio to the ignition Ecu, to the regulator.
          So, when chit happens to me, I just put the DVOM on the alternator and look for an AC component.
          And sometimes the lights flicker.......
           
          Last edited: Dec 16, 2017
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          • gdizzle

            gdizzle Well-Known Member

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            Ok still missing. I have now tried a new Alternator, no change. Along with new ICM, new eCoil. I checked out dizzy for worn or exposed wires...nothing. I also just took car to Oreillys and had them come out with there machine and run tests on charging system etc... nothing wrong. If anything he said it seemed a little high like 15. Which is strange because in my car I have a volt gauge and it only says 14.3 - 14.7. Never 15. He also said battery is fine.
            I also removed each spark plug, they all look the same, nice and tan. I also removed each wire while it was running and they are all getting spark.
            where to next? my gaps are at 45 since I am running HEI. do you think that is too much and could cause misses??
             
          • cdnEHbody

            cdnEHbody Well-Known Member

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            I run a bit less. Close them a bit. Couldnt hurt
             
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            • nm9stheham

              nm9stheham Well-Known Member

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              Put an analog voltmeter on the + feed to the ignition from your relay and make sure the voltage is not dropping out there. If it is, then look to the ignition switch and the feed to the relay, the relay etc. I'll say it again.... your initial symptom description jives with the key switch dropping out the power to the ignition and to the charging system. (You could also use your dash meter temporarily wired to various spots to monitor this.)

              Also borrow an accurate meter and check the voltage to the battery when at fast idle; your dash voltmeter is only so accurate. A good way to check a meter for accuracy for automotive uses is to measure the voltage on a fresh, unused 9V battery; they are consistently right at 9.6-9.7 volts if new and fresh.
               
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              • gdizzle

                gdizzle Well-Known Member

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                Ok so an update of sorts. I removed the plugs again, and reset the gap down to 40. And now the miss is hard to find. And it doesnt drop the voltage down. At the same time I also replace the wire that was coming off Alt going to the ICM, as that wire was looking strange, like the wire inside was fading?? I will keep testing it out and see if that Miss comes back. thanks for all the help. I see on Youtube, people take a water bottle and spray under the hood at night, and you can see small arcs. Has anyone tried that on the Slant??
                 
              • nm9stheham

                nm9stheham Well-Known Member

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                Very good. I have not tried the misting thing.... sounds like a way to get shocked LOL
                 
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                • Slantsix64

                  Slantsix64 Well-Known Member

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                  Do you have your spark plug cables in the right order? 15 too young 36 too old 24 just right just a thought
                   
                • Killer6

                  Killer6 Well-Known Member

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                  I've used the water bottle misting on just about everything, Std. points, HEI, DIS, COP, You name it,.....if there's a high tension leak it will easily help it rear it's ugly head.
                  No electrocutions in 33+ years of it, just don't test it with Your tongue like a 9V, or feel compelled to grab it where it's sparkified & sizzlin'!!!!:rolleyes:
                   
                • nm9stheham

                  nm9stheham Well-Known Member

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                  LOL.... probably not a good idea for someone who had a heart attack before (like me)....
                   
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