High reading coil no spark

Discussion in 'General Discussion' started by sam maxworthy, Feb 9, 2020.

  1. My coil is reading 19,000ohms and I have no spark I have an electric distributer.
     
    Last edited: Feb 9, 2020
  2. Its high maybe, but not open circuit, so there ought to be some spark if 12 volts is pulsing on the primary. Coils tend to break down causing misfires rather than die totally.

    I would suspect points not opening, breakage in the distributor cap (carbon centre finger snapped off) , the condenser or an electronic unit first.
    Less likely - distributor not fully down so its not rotatimg.

    And the most likely failure on electronic unit is human error, connecting the wires black to black. Which happens because the colour code for ignition switched circuit is black in a VW, which is where the red wire from the electronic unit should go to coil +.

    Check with a test light from coil negative to ground that it goes on and off while cranking.
    On all the time or off all the time means no pulse to the coil and so no spark because of problem on the distributor side of things . Its harder with a modern digital meter - they measure 3 times a second and go crazy with the pulses and the voltages.
     
  3. Where are you measuring it?
     
  4. This ^ primary or secondary....?
     
  5. This is the secondary reading, I’ve also tried my multi meter on the coil with it plugged in with the ignition turned on but it reads 0.9v but putting it on the + and earthing it on the engine reads 12.3v has the coil broken down to not read 12v all the way through
     
  6. 0.9 volts to ground suggests its likely you have a damaged electronic module. If it were using (metal to metal contact breaker) points it would switch from 0 volts or maybe a bit more, and then to 12.3 volts and back again as you turn the engine over by hand.


    I happen to have measured my electronic module and that goes down to about 0.9 volts and up to 12.3 (or whatever the battery voltage is) as the engine rotates and its all working..



    The points connects the coil across the battery, one side is at 12.3 volts the other at 0 volts. The current is about 3 amps through a 4 ohm coil. So yes it is meant to periodically have one side shorted to chassis.

    The coil stores energy in a magnetic field. The points open, the three amps stops flowing, and the magnetic field from the current collapses fast and causes high voltages to appear.

    See if you get sparks by taking the distributor lead off the coil and tapping it on the tag you just removed it from.

    Another thing to tell an electronic unit is that there will be a red and a black wire coming from the distributor to the coil.


    Another brain fail is having the reversing lights connected to the contact breaker tag side of the coil instead of the black ignition switched side.. Every time you engage reverse, the engine stops as the lights short out the points. .
    Some gearboxes will operate the reversing light switch without the gearbox being fully in reverse, but with the gearstick partway to reverse, still in neutral with the engine running. Mine does.
     
    Last edited: Feb 9, 2020
  7. I would imagine 0.9 volts is the diode drop.
     

  8. Okay thankyou, so even though the secondary reading is nearly twice what it should be I should still get spark but it just wouldn’t run very well? The primary reading also is a bit low at 2.6 ohms I don’t have my rear lights attached at all, it all seems wired correctly and the rotor arm does move fine and I removed the centre lead from the dizzy and it does not spark when rotating the engine
     
    Last edited: Feb 9, 2020
  9. Do you have an electronic module ot points ?

    If there is a black brick with red and black wires in the distributor and a magnetic ring below the rotor arm, its electronic..
    The 0.9 volts is a sign of this too, being the voltage across a transistor inside the module with the current flowing through it.



    If its just a green wire and a metal cylindrical condenser on the outside of the distributor, thats points.



    If the coil has a primary resistance of 2.6 ohms and a high secondary resistance, this is likely to be a "high output" coil. E g. there is a Pertronix Flamethrower model like this . Trouble is that it draws more like 5 amps (12.3 volts/2.6 ohms) rather than three amps.
    It is intended for high revving Beetle engines( twice a bus RPM) with points or beefy electronic ignition units where there is a big box beside the coil with electronics. You just dont need magic ignition stuff in a bus where the ' official' RPM limit is more like 4000 rpm.

    Some older electronic units turn "on" with the engine stopped and ignition on. They then get hot and burn out. So it will work OK for ages and then die while you are working on something with ignition on.. Accuspark and Pertronix Ignitor III units dont turn on when stopped, and Accuspark also use thermal grease for heat dissipation.

    Check the coil works by manually taking a wire from coil - and earthing it with nothing else connected to coil with 12 volts on coil +ve: - it should spark.

    If it is a high output coil and a fried electronic unit, you can go back to points..
    Or sell the working coil and buy a Bosch Blue coil, then fit new electronic ignition module or points.

    Take a picture of the coil and inside the distributor.
     
    Last edited: Feb 10, 2020
    Gingerbus likes this.
  10. Hi it is electric and I think my coil must be a high out put
     

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  11. As a first step, I’d get rid of that coil and fit a bog standard Brazilian Bosch coil. Or a Beru if you can find one. You don’t need a super-duper coil for a bus engine.
     
  12. Is High Reading near High Wycombe?
     
    Iain McAvoy likes this.
  13. That coil will be OK with points and a condenser. Thats the cheap get you going fix.
     
  14. I was going to get the standard bosh coil but it says not for electronic ignition does this mean it won’t be strong enough
     

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  15. Also My engine seemed okay then got sluggish and would stall just from taking my foot off the clutch, after that I couldn’t get it running again so I stripped the heads etc of the engine tarted them up fitted all new seals spark plugs ht leads ground the valves in and still nothing just winds over until the battery dies
     
  16. The Bosch one will be fine with an electronic ignition unit (but is incompatible with the electronic one VW fitted, which you won’t have).
     
  17. Oh that makes sense thankyou. Do you think it’s worth a shot seeing if it’s the coil ?
     
  18. I think it’s worth retiring the Accuspark coil ;)

    I used the Bosch one for years. It was fine.
     
  19. Oh okay it is basically new though I’ve never driven anywhere in it I put it in about a year ago and only ever driven it out the garage and back in is it likely a faulty coil from new
     
  20. Don’t know whether that’s the cause of your problems. Substituting a new coil is a good place to start.
     

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