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Intermittent Spark from Coil - Need Assistance Please


EPK

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I think you mean both sides of the coil ?

 

Well. Look at the points and make sure the wiring from condenser to points is not open or grounded.  

 

GL,

Ray

Stop reading this! Don't you have anything better to do?? :P
Two running things. Two broken things.

 

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Well, there's your problem.  When the points are closed, you ought to have ground on coil -.

When you meter the arm of the points, do you see 12v or 0v?

If 12v, then your points aren't grounding for some reason.

If 0v, then the wire between the points and coil - isn't doing its job.  You

can make a jumper yourself and connect the two.

 

Wallah, one problem solved...

...it's not impossible you have several, he says, pessimistically!

 

t

 

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Riddle me this:

 

Two wires connect to the coil.  I disconnected the wires from the coil to do the following.

 

With the ignition on, one displays 12 volts and the other displays 3 volts.  Shouldn't one be 12v and the other zero volts?  I'm placing my voltmeter on the end of the wire (that would connect to the coil) and grounding the other voltmeter lead.

 

This doesn't makes sense to me but I'm not as well versed as y'all.  

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38 minutes ago, EPK said:

 

@TobyB

 

I see 12.x volts on both sides of the coil.  So, they must not be grounding right? 

 

I forgot to say that you should be testing at the points arm, as per what Toby says  Keep all your wiring connected to both sides of the coil and to the points.

With the points open the resistance from the stationary side of the points to ground should be zero to check if the points ground.  The points are just a simple switch to ground from the coil.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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15 minutes ago, EPK said:

and the other displays 3 volts.

Check from the distr housing to battery ground, it should be zero volts.  The points trigger wire should be zero volts with the points closed.

Edited by jimk

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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34 minutes ago, EPK said:

and the other displays 3 volts.

I had a thought and set up a spare instrument cluster on a 12V power supply and the tach will back feed 3 volts to that wire.  Something new for me to know.

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A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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2 hours ago, EPK said:

@TobyB

 

I'm 100% certain that my points are closed.  Given this, meter to ground shows that both the + and - posts of the coil produce 12 volts.

 

@ray_

 

Continuity is ok on the positive wire.  I removed it from the coil and condensor to check.

 

I'm curious what Toby has to say about 12 volts on both sides of the condensor.

One side of the coil must be connected to ground if the points are closed, since that is the coil "charging" cycle.  This suggests that your points are not truly closed, or there is a break in the wiring someplace on this side of the circuit.

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I found this nice diagram on the Internet to which I added nodes for reference.  Referring to the nodes on the diagram, a step by step check may turn up something:

  • With ignition switch off, what does ohmmeter show between A and C?  Should be around 1 to 3 ohms.  If not, bad coil.

  • What does ohmmeter show between B and F?  If open or dead short, bad coil.

  • Do your points work?  Disconnect D from C and check with ohmmeter between D and E.  If continuity does not vary between open and short, points are bad.

  • Check continuity between E and chassis.  If open, broken wire.

  • With ignition switch turned on, do you have 12 volts at A?  If not, bad wire to coil.

  • With points open, do you see 12 volts at C?  If not, points stuck closed.

  • With points closed, is C at zero volts?  If not, points stuck open or wire between C and D broken.

  • If all the above check out, if no spark when you open the points manually, then your HT leads or coil are suspect.

 

Ignition Nodes.png

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Thank you to everyone.  I worked on this until mid day today and then had to quit.  I needed a break and distraction otherwise I would go nuts.  I will read over the other comments and try those next.  

 

I appreciate everyone's support and help.

 

Erik

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If you own a simple 12V test light you can use that to diagnose the ignition primary circuit, probably easier than with a dvom/multimeter. Attach the clamp on the test light to a good ground then touch the probe end of the test light to the positive terminal on the battery or the large 12V lead at the starter motor, just to make sure the test light is functioning. If yes, touch the probe to the + side of the coil. Key on, test light comes on, key off, test light goes out. If no, the test light never lights then you don't have voltage to the coil. Stop and determine why, repair problem then continue testing. If yes, touch the probe to the - side of the coil and crank the engine. Test light should flash on and off while cranking. If yes the primary side is functioning normally. If no, and the light remains on, the points are open all the time OR you have a break in the wire to the points OR the distributor is not grounded properly OR you've got the wrong wire connected to the points/coil. If no and the light remains off, the points are closed all the time OR you have a dead short someplace in the wire that goes to the points OR you have the wrong wire connected AND a dead short in it someplace.

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@torquewrench80

 

Here's how far I made it:

 

Probe on - side of coil, cranking engine and the light stays on.  

 

- I don't think the wires are connected wrong.  I am attaching the wire that displays 12v with key on, to the + side of coil.  I tried reversing wires for the heck of it as well.

- I don't think the points are failing to open either as I turned the distibutor shaft by hand prior to installation and they open and close.  I checked the gap as well (.016).

- I don't think there's a break in that wire and here's how I tested that.  I disconnected the wire from the condensor and the wire from the + side of coil and checked for continuity using the ohm meter.  It goes to zero so there shouldn't be a break.  The - side of coil has no continuity to the condensor wire.

- Distributor not grounded : I can only imagine that this is the case.  It would explain my issues for sure and although, as stated earlier, the ground wire doesn't appear broken it could be hard to detect.  These distributors unfortunately don't have a separate ground like many that I've seen and instead rely on that little ground wire inside going to the body. 

 

If that's correct, I need to fix it this week in order to make my rally and I'm not sure how to do that on my own.  Jeff Schlemmer usually has a long wait and I don't expect him to expedite this for me.  

 

Thoughts?  Did I miscalculate somewhere?

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Hi,

 

If the distributor isn't grounded, you will definitely have problems.  It's that node E to chassis that you are referring to in my diagram above, correct?  Can you take an ohmmeter and do a continuity check to chassis to confirm?  Also, at high currents, poor contacts become very resistive so an ohmmeter reading cannot always be trusted.  Is there any way you can temporarily run a  wire from the points to chassis?

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I would set the point gap at .014, as per the blue book factory workshop manual. Then check it for the proper dwell angle once it's running. There are some variables there, we can cross that bridge later.

 

"I disconnected the wire from the condensor and the wire from the + side of coil and checked for continuity using the ohm meter.  It goes to zero so there shouldn't be a break.  The - side of coil has no continuity to the condensor wire." 

That's a little confusing to me, particularly the last sentence. You should have continuity on the wire to connected to the - side if coil and at the condensor. Your description sounds as if something is not connected to the proper terminal at the coil. Whenever I had a vehicle in the shop that ran properly when it came in and either refused to start or ran poorly when I was finished the first thing I did was look for something that I did wrong to cause the problem. It's quite easy to make a mistake and there is no shame in it, we all do it. Not saying you did, only that it's a possibility Are you using a 12V test light as I suggested or a dvom?

 

Use your 12V test light to check if the distributor is grounded properly. Place the clamp on the positive terminal of the battery or the 12V lead at the starter and touch the probe to the distributor case, the light should come on. If the light doesn't come on, the distributer case is not grounded properly, determine why and repair. I can't imagine that it it wouldn't, you'd have to have no engine ground in that case. Continue using the test light to check for grounds. If the light comes on, the distributor case is grounded properly, then start back tracking all the various ground points - the ground wire from the contact breaker plate to the dist case, the breaker plate itself, the contacts (points) and so forth back to the coil - side. 

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