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Old 01-07-2013, 09:45 PM
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Bad Ignition Coil?

Hey everyone. I just bought a 69 Mustang and it starts and idles fine. After idling for about 20 mins or driving for about the same amount of time the car will die. I have to let it sit for 5 mins or so then it will start back up and run again and then do the same thing. When it begins to die it starts to jerk and stutter. I have taken the + coil wire off and touched it to the post to see if it gets a spark and it doesn't seem to get one right away after it does this. After it dies the carb is still getting fuel. I have tested the coil with a multimeter and it seems fine but it does get 12 volts with the key on / engine off and the same with the engine running. Any ideas what could be causing this behavior?

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Old 01-08-2013, 12:58 AM
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Do you still have points ignition? If so, you shouldn't be getting 12 volts in the run position, only while you're cranking.. Should be around 8-9 volts I believe Could be the coil is heating up and/or shorting because of this. It'll also burn your points out quicker.
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Old 01-08-2013, 03:46 AM
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Coil is def a suspect....... also check your dizzy cap and rotor for a hairline crack. I had one that had a hairline crack, it was an after market etc..... when it heated up it would start cross firing and stumble and die..... ended up replaceing them both and the problem went away.
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Old 01-08-2013, 06:24 PM
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Thanks guys I'll check these items and post back how it goes.
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Old 01-08-2013, 08:11 PM
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One more thought. I once had a Dodge Red Ram in a model A. Similar issue. The lead to the points was grounding on the distributor case inner wall. Didn't happen when cold, only after warm up. Good luck!

PatM
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Old 01-18-2013, 09:28 PM
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Another possibility is the RFI capacitor grounding
out when it gets hot. It's the small cylinder connected
to the coil that suppresses radio static.

Simply disconnect it for testing.
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Old 01-19-2013, 11:34 AM
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When it dies try opening and closing the points by hand while checking for spark at the coil wire. If there is no spark and the points are ok it is most likely the coil. A better test would be to disconnect the distributor at the negative side of the coil and using a jumper wire short the negative coil post to ground while checking for spark at the coil wire.

Also a good first test is when it is not running check to be sure there is voltage at the positive side of the coil with the key on.

I have a wiki article on troubleshooting ignition that will bring you through it step by step. Just search the wiki for ignition troubleshooting.
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Old 01-26-2013, 06:50 PM
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Just a quick update, I have changed the coil, condenser, cap, and voltage regulator. I was getting about 16 volts at the battery with it idling until I replaced the regulator. I will be double checking everything tomorrow as it is still doing only much sooner now. When it dies I am still getting voltage to the coil. There are 3 fuel filters on the car so I will check those as well. Thanks for all the help and suggestions. I will give an update soon.
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Old 01-27-2013, 05:12 AM
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Although your coil is a suspect...have you ruled out vapor lock?
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Old 01-27-2013, 06:55 AM
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At this point, I am leaning towards what PatM said. The lead to the distributor from the coil could very well be shorting to ground at the distributor housing,keeping the coil grounded which would kill the motor.
I have personnaly seen this a few times in all my years of wrenching , it does happen.
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Old 01-27-2013, 09:38 AM
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bad coil

That will be an interesting one to test. You going to just let it idle until it does it again while running an OHM meter on it? Intermittent electrical problems are always a pain in the backside. Good luck with it and keep us posted on how it turns out.
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Old 01-27-2013, 09:53 AM
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The best way would be to connect a test light lead to bttery positive and the light to the ground side of the coil (lead going to points) if the lead gets shorted the test light will illuminate and stay on as long as the short to ground is present.
You can use a regualer 12 volt bulb 1156 whatever , just solder a few leads to it and connect to system at the respective test points as described. Voila just drive till it quits...status of the light will indicate if that is the issue or not. LA Tech
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Old 01-27-2013, 10:07 AM
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Quote:
Originally Posted by kaoticmustang View Post
Just a quick update, I have changed the coil, condenser, cap, and voltage regulator. I was getting about 16 volts at the battery with it idling until I replaced the regulator. I will be double checking everything tomorrow as it is still doing only much sooner now. When it dies I am still getting voltage to the coil. There are 3 fuel filters on the car so I will check those as well. Thanks for all the help and suggestions. I will give an update soon.
16 volts is most likely overheating the coil or condenser.
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Old 01-27-2013, 10:45 AM
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[QUOTE=kaoticmustang;1632052] After it dies the carb is still getting fuel. [QUOTE]

Why check the fuel filters?
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Old 08-24-2013, 12:03 PM
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Quote:
Originally Posted by T-bucket23 View Post

I have a wiki article on troubleshooting ignition that will bring you through it step by step. Just search the wiki for ignition troubleshooting.
This it what I got at wiki
The page "Ignition trouble shooting" does not exist. You can ask for it to be created,
8-24-13
Pat
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