Fluctuating neg. to ground on ignition coil

Small Block Mopar Engine

  1. nm9stheham

    nm9stheham Well-Known Member

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    Yes... the cam question dropped to the bottom of my list when the OP showed the smooth operation in his latest video. But valvetrain-related is something like erratically sticking valves.
     
  2. Stephan D

    Stephan D Well-Known Member

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    Measured all the spark plug wires today, got between 11000 and 12000 Ohm except for the short one between the ignition coil and the distributor cap that got around 5000 Ohm.

    Spark plug wires are Accel radio suppression wires 8 mm.
    20200621_141309.jpg
     
  3. nm9stheham

    nm9stheham Well-Known Member

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    That is higher than I usually allow. I find them more commonly to be in the 5000 ohm range, + or -, for the main wires, when new.

    I see this link that discusses spark plug wire resistance in some detail. It indicates that your resistance range is OK, but I never run with them with that high resistance. Usually when they get that high in resistance, they are getting a bit old. SPARK PLUG WIRES

    The whole purpose of the resistance is to slow the rate of the current rise the spark, to suppress radio and electronics interference. But too much resistance, then the spark energy gets suppressed so much that it may or may not fire the mixture. This is somewhat suspicious with your idling miss....especially as it occurs with heat.

    What spark plug model are you using? And to what distance is the gap set?
     
  4. Stephan D

    Stephan D Well-Known Member

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    Got in touch with an old collegue that is an electronics freak, so he will bring his oscilloscope today and try to do some measurements.

    Any input on what to look for would be appreciated.

    I suppose it´s the secondary pattern that could be interesting?
     
  5. Stephan D

    Stephan D Well-Known Member

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    I will check and take some spark plug pictures when we mess with the oscilloscope today.
     
  6. Stephan D

    Stephan D Well-Known Member

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    Spark plugs are NGK BP6ES, looking like this:
    Spark Plugs NGK BP6ES.jpg
     
  7. 512Stroker

    512Stroker We are all here because we are not all there.

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    Need a pic from the side showing ground strap
    And a view looking in the plug
     
  8. Stephan D

    Stephan D Well-Known Member

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    Sorry, english is not my native language...

    What ground strap?

    Looking IN the plug, is that possible?
     
  9. 512Stroker

    512Stroker We are all here because we are not all there.

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  10. Stephan D

    Stephan D Well-Known Member

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    Oh, that was interesting!

    I had no idea that much could be read from the spark plugs.

    I had the valve seals replaced this spring as it was smoking blue at warm up after sitting a couple of days.

    Not sure if the new seals solved the problem as it still smokes at warm up, maybe there was old oil left since before the valve seal replacement?

    So today I took the little Mopar for a spin on the highway, with a lot of full throttle accelerations up to 5000 RPM, it smoked at first but later there was not a trace of smoke when I pushed the throttle hard.

    Removed spark plugs and took some pictures, it´s hard to get the colours right, but the plugs are very clean after this run and the colour is sort of grey-ish, with some changes at the ground strap bend, see pictures and inserted arrows below.

    I'm still not sure of what I see, still confused but on a higher level.
    Tänsdtift 2.jpg Tänsdtift 1.jpg Tänsdtift 3.jpg
     
  11. 512Stroker

    512Stroker We are all here because we are not all there.

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    Nice. I am glad you liked the information.
    Yes sparks can tell you a lot about your engine
    Reading the plugs is the key to tuning any engine.
    The timing on the plugs is very correct - don't change.
    Air fuel ratio looks lean.
    Need to have more regular driving miles to get an accurate reading.
    Drive the car at normal speeds for 100 miles and read the plugs again.
    Good luck
     
  12. Stephan D

    Stephan D Well-Known Member

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    Finally got in touch with a friend and his oscilloscope, not sure of what we found out.

    Can anyone interpret these graphs?

    Tried on a single spark plug wire on cylinder 1, looked like this:

    cylinder1.png

    Wire from the ignition coil, it seems to differ a lot between the pulses to each cylinder:

    Spole.png

    Spole5.png
     
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