Killed Two Distributors and Don't Know Why!

Electrical and Ignition

  1. 70DusterBob

    70DusterBob Well-Known Member

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    I have a 408 Stroker in my 70 Duster. Just had it put in. After the installation, the distributor blew out when I tried to start it after about 20 miles and maybe 10 starts. I went to start it an no spark on the 11th start.

    So I figured well, it's probably the distributor, it was brand new, a Pro Form brand dist. I replaced it with a semi-stock one that lasted about 3 starts and ran maybe 5 min. On the fourth start, no spark. So that tells me it's not the distributor, lol. I plan on changing out the ballast resistor, and the distributor again, but this is getting pricey. I don't know for sure the ballast is what blew them out, is there any way to tell what it is? Diagnostic?
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    You are going to have to provide some "real" details about your ignition.....are you talking about a breakerless/ magnetic firing a Mopar box or just what?

    IT IS possible that (if that is the case) that the Mopar box has some sort of electrical problem that is causing current flow through the magnetic pickup and damaging it.

    If this is a "ready to run" or something similar, could be mismatch of coil / ballast or even a coil going bad. What is the history of it?
     
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    • 70DusterBob

      70DusterBob Well-Known Member

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      Sorry for the lack of details. I was in a bit of a hurry yesterday. I don't have constant access to the web. I have to come over to a friends house to access it so I was too brief.

      It is the ECM that is stock with factory electronic ignition. The coil is a MS Blaster, high performance or matching ballast, but the thing is the only thing that changed between it running with the old motor in it, and the distributor short I guess it was, after I had the engine installed was the distributor, here's the dist I put in it after the engine swap:

      Proform Electronic Distributors 66990

      Before I put the back up distributor on, the one that was running in the car before I had the engine swap, I used a back up ECM a back up ballast and a back up coil. I actually changed the four parts because I didn't know what it could be. So I had a the old dist. that was running before the swap, a back up ECM, a back up ballast, and a back up coil and it still did it with all these parts. But do keep in mind these parts are 12-13 yrs old, so it could be any one of these components malfunctioning now. I am just leery because it quit on the start again, wouldn't start after running 2 min before I tried to start it and it wouldn't start.

      I was thinking maybe I fried something using the proform dist. but have no idea exactly what to replace. I don't know if I have the dist mismatched or not. I just got a 3rd distributor, but this is a factory or stock model... I just don't want to blow up this one too.

      Is there anyway some other part of the electrical system could cause this malfunction? They did work under the dash/behind the instrument panel. I don't know if there could be a short somewhere else, or what. Seems like it would be the ballast to me, but not real sure.

      Thanks for your help.
       
    • Johnny Mac

      Johnny Mac www.blueprintengines.com FABO Vendor

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    • 70DusterBob

      70DusterBob Well-Known Member

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      Hey Johnny,

      Yeah, I want to upgrade the whole thing really, but can't afford it right now. I would hope it is a simple fix. The ballast is $15. If it's more than that, I will probably kick the sleeping dog that bit me and come knocking on your door again. lol
       
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      • 67Dart273

        67Dart273 Well-Known Member

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        I re-read your post.........your trouble is not necessarily the distributor. I posted some troubleshooting details on these "someplace.............."

        .........See if this works...........

        ===============================================================

        Here's a post I made about the simplest way I know to get across testing the ECU/ ignition parts

        You need a coil, the ECU and the distributor

        Lay it out on the bench. Follow the diagram. Find the two distributor pickup terminals on the ECU. Hook them to the distributor

        Hook the ECU case to battery NEG

        Coil does NOT need grounded

        Distributor does NOT need grounded.

        Hook coil + to the power lead terminal on the ECU. Get a clip lead hooked there and let dangle. This is your battery "hot" when you are ready

        Hook something from coil "case" to a probe for testing spark.

        Hook up your power clip lead. Twist the distributor shaft while holding the test probe near the coil tower. The thing should make sparks

        If not, unhook distributor. Take first one, then the other pickup clip leads, and "tap tap" ground them at the battery connection. Coil should make 1 spark each time you do so.

        If not, try another coil. If that does not fix it replace the ECU

        IF you hook it all up and it WORKS, then there is something AFU in the car harness. SUSPECT a bad ECU connector OR a bad DISTRIBUTOR connector
        =============================================
        This is all you need to test the basics of the ignition. You can easily test the ballast separate. A battery, the ECU, distributor and a coil, and of course some test leads

        2ai0wsj-jpg.jpg

        Below, the basic diagram for a 4 pin ECU

        166lmj7-jpg.jpg

        Below, the wire for testing spark. I use my 12V test light. No, LOL the spark won't blow up the bulb

        166lmj7-jpg.jpg

        Below, the ground connection. ALL you need is one wire from batt NEG to the ECU case

        xawjl-jpg.jpg

        Below, the two distributor connections. In the car these are polarity sensitive, but for testing does not matter

        b3opvm-jpg.jpg

        Below, the coil NEG connection

        6jfywp-jpg.jpg

        Below, battery PLUS connection, one wire to this terminal of ECU and jumpered over to + side of coil


        11lqu5l-jpg.jpg

        Below, all hooked up and ready to test (except for battery ground). Should produce sparks at least 3/8" and typically 1/2" long

        1zzoya0-jpg.jpg

        Below, distributor "one wire" test. I have removed the other distributor wire for simplicity. Take the bare connector end or this clip lead (the yellow) and with everything hooked up, ground it repeatedly. Each grounding should result in a spark (In this photo you need to hook up the ECU ground wire, I left it off for the photo)

        vgitld-jpg.jpg
         
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        • 67Dart273

          67Dart273 Well-Known Member

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          ^^That was more intended as a step by step how it works^^

          Also.......

          Wiggle test all connectors , the ECU, the ballast, and the distributor connector. work them in/ out to feel for tightness and scrub the terminals clean

          Disconnect the dist connector, hook your meter to the distributor on AC voltas and crank the engine or spin the dist. It should generate about 1 volt AC.

          Inspect the reluctor and pickup for rust or debri, or strike damage, feel the shaft for bearing wear and check the reluctor gap at .008" (that's inches not metric)

          With the system hooked up, put your meter on coil +. Crank the engine using the key and read the meter while doing so. Coil+ shoud read "same as battery" and more than 10.5

          Read coil+ voltage with key in run. Should be between 6--10 volts. If it is same as battery (12.xx) the coil is not drawing current

          Measure coil NEG with key in run. It should be quite low, no more than 2V and should really be less. If it is 12V the coil is not drawing current and CHECK THAT THE ECU IS GROUNDED. It MUST be grounded. Scrape around the firewall bolt holes and the rear of the ECU and remount tight with star lock washers.

          EDIT.........One thing I left out. With system hooked up normal in car, disconnect distributor. Take the engine harness end of that connector, and with key in "run" tap the bare end of that connector to ground. Each time you tap it to ground, the coil should produce one "snap" spark. Use a solid core wire for testing. You don't even need a spark/ coil wire You can use a wire probe like in the earlier posts

          "Rig" a wire/ spark plug or buy a spark gap type tester to test spark. I use a Lisle as it's adustable, and they are not expensive

          Like this: Connect to coil and ground the other end

          l50850__57428.1406568988.jpg
           
          Last edited: Mar 17, 2019
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          • 70DusterBob

            70DusterBob Well-Known Member

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            Thank you so much for that detailed explanation. I will need to print it, but I will see what the results are.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Del has laid out realy good info above. Print that. redaw the diagram yourself so you will remember what each wire connects to.
            Slow down, take a little time to get a hang of what each part does.
            Its actually a very simple system, and pretty easy to seperate which component failed.
            Distributor. The connecting wires go to a magnetic pickup. Take the cap off and look. Every time the point on the reluctor goes by the pickup, a small electrical pulse is sent down the connecting wires. Yes, the pickups occasionally go bad. Very occassionally.
            ECU. Amplifies the magnetic pulse to open and close the ground connection of the power flowing through the coil. The ECU itself needs power to run, but not a lot.

            upload_2019-3-15_9-35-24.png

            Ballast Resistor Reduces the power going to the Coil when the engine is running, and in most cases also the ECU.
            Coil's Primary Resistance and the Ballast Resistance together regulate the current through the coil. That's why these need to be matched.
            During start, voltage is only 12.5 Volts at best. That's one reason why the ballast resister is bypassed during start.

            Illustration from 1973 Electronic Ignition Repair p. 3
             
            Last edited: Mar 15, 2019
          • 70DusterBob

            70DusterBob Well-Known Member

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            Thanks for the manual, very helpful. I saved a link to it. From what it says, the ground between the ECU and the firewall may not be very good, and the pins need to all be sanded and checked for tightness where they meet the wires...

            After that I will dare to take another stab at a start, with a new ballast.

            Thanks
             
          • 67Dart273

            67Dart273 Well-Known Member

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            Please note edited post above
             
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            • 70DusterBob

              70DusterBob Well-Known Member

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              Hey '67,

              Is there anything possible outside of the wiring harness in the fire wall, the coil, ballast, ECU or Distributor that could be the problem? I plan on running some diagnostic work on it before I try starting it again. I don't think I can do everything you recommended, but I will try to do my best. I was just wondering if there is anything outside of the normal four parts that could cause a distributor to fail...
               
            • 70DusterBob

              70DusterBob Well-Known Member

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            • 67Dart273

              67Dart273 Well-Known Member

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              Well sure the harness has be be intact, the connectors and terminals have to be making connection. "in a rare case" I found an ECU connector evidently the wire going into that connector was intermittent right at the terminal crimp, inside the molded rubber connector. Since that harness/ connector does not get moved very much, you have to wonder if it was "shaky" from the getgo Just an example
               
            • 67Dart273

              67Dart273 Well-Known Member

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              "Take first one", here highlighted below... first one what?:

              Poorly worded. Disconnect distributor connector. Take the engine harness end, not the distributor end, and tap the bare connector pin to ground

              If not, unhook distributor. Take first one, then the other pickup clip leads, and "tap tap" ground them at the battery connection. Coil should make 1 spark each time you do so.


              If not, try another coil. If that does not fix it replace the ECU

              It might be that you did not actually "kill" a distributor. Either there is some problem with the system leading you down the wrong road, or the distributors are "right on the edge" of being able to trigger the ECU (check condition of pickup/ reluctor and reluctor gap) or you just plain got "lucky" and two of them failed.

              I've never heard of this but "I guess" it is possible that a problem in the module might put DC current on the distributor connections and burn it up. The problelm is I have no reference for this.
               
              Last edited: Mar 17, 2019
            • AUSA66

              AUSA66 FABO Gold Member FABO Gold Member

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              Also check your coil for tracking down the side of the coil i have had 2 x MSD blaster 2 coils go now. check for a black line down the side from the centre to 1 of the studs
              The second 1 went right through the MSD insulator then into the Fitech injection plug also damaging the Fitech which in turn dumped a heap of fuel into the bore
              When i tried to start it had pumped that much fuel into the bore it went past the rings into the sump .
              I had flames shooting out the rocker cover breather as the flashing coil was igniting the vapours from the breathers
               
            • 67Dart273

              67Dart273 Well-Known Member

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              ^^That is a good point, and as ignition performance goes up, it becomes a possibility that the rotor can "punch through" that is below the contact, through the rotor and arc down to the shaft. Use a flashlight and examine the rotor carefully. Neither of these, generally will cause a complete loss of spark, just really poor performance and "missing"
               
            • 70DusterBob

              70DusterBob Well-Known Member

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              Okay will do.
               
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