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Thread: Intermittent spark

  1. #1
    Registered User Weasel73240Z's Avatar
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    Default Intermittent spark

    As you can tell by my avatar, I got the motor and tranny back in this week, and tried starting today. It misfired a few times, but never actually ran. I think with some timing tweaks it will go just fine. I got very close, but I seem to have an issue in the ignition/coil/distributor region. I get really good, blue spark sometimes, and no spark other times. I'm using the original points ignition, and the car ran before I tore it down, so I believe all the parts are in good working order.

    I checked all of the connections at the coil, starter, resistor, distributor, battery tightened them all, replaced a few connections. Points spark good with the key in the on position. Theres a good pulse coming off of the negative pole to the points, when I turn the key. I don't know how to check if the main coil (to the dizzy cap) is firing correctly. But I occasionally get a good spark when I first turn the key, then after it fires 5 - 6 revolutions I seem to lose the spark. Other times I get no spark, no consistency. Any ideas? Could this relate to the resistor?

    Also, I have a EI module and dizzy out of a 78, should I install it? I hear it really simplifies things. OR should I try and get the original points system working before I make the upgrade. Thanks in advance for your help.
    Paul Martin
    1973 240Z HLS30-127623 (10/72)
    4.11 R-180, 79 ZX 5-speed, ZX Distributor, ZTherapy SU's

  2. #2
    Supporting Member EScanlon's Avatar
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    Paul, I would suggest to get it running first then do the upgrade.

    First check to make sure the points have enough dwell on them then check to make sure you've reconnected the B/W wire at the Coil correctly.

    To do this, first disconnect the wires at the Resistor. Then, with the Ignition OFF, do a continuity check between the Green/White wire at the Resistor and the Black/White wire at the Coil. If it does NOT check (give a tone, or light up), then check the B/W wire that was connected to the other side of the resistor, you will probably get a tone there. If so, swap the B/W with which you got a tone to the + side of the Coil.

    You SHOULD have continuity between the G/W at the Resistor and the B/W wire at the coil (this is the "loop" portion of the circuit through the Tach).

    This is a simple check but it ensures that the coil, resistor, tach and ignition wiring is hooked up to the right connections.

    Then we'll go from there.
    E
    Last edited by EScanlon; 03-28-2008 at 05:53 PM.

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    Registered User Weasel73240Z's Avatar
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    Thanks E. I have a buddy coming over today with his test meters to check out some things. I am just about at a loss when it comes to anything but basic electrical stuff.

    What I do know is that everything is hooked up as it was before when the car ran. I took pictures of everything before I took it apart, and I had it all labeled. I re-checked the wiring against the original pics. So I'm sure it is wired up correctly.

    No spark I would understand, but spark sometimes just makes no sense to me. Any other ides that I should be checking out today?
    Paul Martin
    1973 240Z HLS30-127623 (10/72)
    4.11 R-180, 79 ZX 5-speed, ZX Distributor, ZTherapy SU's

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    Supporting Member EScanlon's Avatar
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    The reason I mentioned the B/W wire check is that it is one of the most often overlooked re-connections. There are TWO wires both B/W that each connect to the Coil and Resistor respectifully. If you hook them up in reverse, you will not have any spark while starting ONLY while running, but since you need it during the Start you might get an intermittent "spark" when the key is slightly released. (Remember other posts where people have had cross over connections at the ignition switch? That's what I'm referring to.)

    The only other thing I can think of right now is that since it looks as though you painted the engine bay and frame rails, have you checked that all your grounds are making proper electrical conduct? A continuity check will tell you a circuit is there, but you might have to check with other values (resistance/conductivity) to see if there is enough of a circuit to support the current required.

    HTH
    E

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    Registered User Weasel73240Z's Avatar
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    After re-checking that all of the wiring was correct, I tried to get the coil to spark on the block, no go. I just ordered a new coil and resistor today. I replaced all the other ignition stuff, but I was going to re-use the original, 34 year old coil and resistor? Didn't make sense when I thought about it.

    You're right about some of the grounds on the firewall possibly not making adequate contact due to the new paint. I didn't remove any of the new paint, but I did ground a test light on the grounding screws in question and test a known hot 12v, to make sure they were grounded (the test light lit up so I figured the screw in the firewall was grounded). But since the wire was connected to the negative of the battery, it would have shown a ground even if the screw wasn't grounded. Those grounds are definitely worth checking tomorrow.

    Thanks again E.
    Paul Martin
    1973 240Z HLS30-127623 (10/72)
    4.11 R-180, 79 ZX 5-speed, ZX Distributor, ZTherapy SU's

  6. #6
    Supporting Member EScanlon's Avatar
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    I've found that if you simply run a tap into the threads, this often is more than enough to provide a good contact for most applications. However, if they are sheet metal screws, then you need to ensure the screw actually cuts through the paint. This way you don't have to scrape off a bunch of paint around the screw.

    What about your spark plug wires and coil wire? Are they also new?

    FWIW
    E

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    Registered User Weasel73240Z's Avatar
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    Everything (except the coil and resistor) was new. Points, plugs, wires, rotor, cap, condenser, all new. I think the new coil on Tuesday will do it.
    Paul Martin
    1973 240Z HLS30-127623 (10/72)
    4.11 R-180, 79 ZX 5-speed, ZX Distributor, ZTherapy SU's

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    Registered User Weasel73240Z's Avatar
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    So I got spark finally! I got myself a multimeter (and learned to use it) and checked for continuity on every wire from the battery to the starter, to the ignition, to the tach, back to the resistor, to the coil, etc., changed all of the terminals to gold plated. I checked the coil and resistor (both within specs for resistance so I used them) re-gapped the points, gave everything one last good cleaning, sandpapered 'em all, etc., and good SPARK at all 6!

    Now that I have spark, I have to figure out how to get these carbs working properly. My first set of SU's so I have my fingers crossed. Seems like there isn't enough fuel to get it started right now. I have the "Just SU's" video from ZTherapy, I should probably watch that, huh? (Yeah stupid, you should). I understand that these carbs need to run really rich until they warm up (is that correct). I guess I should start a new thread in the Carbs forum tomorrow.

    Thanks to everyone for the help, as usual.
    Paul Martin
    1973 240Z HLS30-127623 (10/72)
    4.11 R-180, 79 ZX 5-speed, ZX Distributor, ZTherapy SU's

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    Registered User Bonzi Lon's Avatar
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    By all means watch that video. I've never been in a carb in my life (holly, carter, AFB, tillitson etc.) watched the video twice then took carbs off, took completly apart, cleaned up everything and back together again in no time. I know how and why they work now. Yep, they need more fuel when cold, that is where the properly adjusted chokes come in. Good luck.

    Bonzi Lon
    1973 HLS30-168500
    1968 SPL311-18100
    1969 HLS30-000110 SOLD Shipped to Dubai UAE
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    Ones and Zeros

    "We drive only blue cars." Dishwalla

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