08-19-2019, 04:00 PM | #1 |
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Coil failure ?
As I was driving my ‘31 Model A home from the local gas station yesterday, the engine suddenly died. A little roadside diagnostic work suggested an ignition issue - confirmed later after being towed home.
Points and condenser were replaced several months ago, engine timing is right on. Although there is absolutely no spark, the ammeter shows deflection as the starter cranks the engine over - from the points opening and closing. I suspect the coil, although I guess the condenser could be part of the issue as well - it’s an original style one installed in the original distributor. The coil is an original one - almost 90 years old. I‘Ve never had a coil failure on this car in the 50 years I have owned it. Has anyone else experienced a sudden coil failure ?? Thoughts ?? Thanks - Jim |
08-19-2019, 05:26 PM | #2 |
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Re: Coil failure ?
Well, it’s obvious the coil is trying to work, because your amp meters moving. Have you checked for spark at the coil wire to ground. Coils do fail, but not as often as people think.
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08-19-2019, 05:43 PM | #3 |
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Re: Coil failure ?
yes - I pulled the high voltage wire out of the dist cap and held it close to one of the head nuts while cranking the engine with the ignition switch on - absolutely no spark. Also - after the first few seconds of cranking, the ammeter stops deflecting ‘normally’ each time the points open and close and starts swinging back and forth - showing discharge and charge- as if the coil is generating a back voltage - never seen this before. I suspect the coil has an internal short.
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08-19-2019, 06:50 PM | #4 |
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Re: Coil failure ?
Maybe the cutout opened up disconnecting the generator from the battery, the generator voltage goes high because it is not regulated by the battery and the excessive voltage overheats the coil and damages the coil windings. Ed
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08-19-2019, 06:51 PM | #5 |
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Re: Coil failure ?
Check the coil for carbon tracks . Carbon tracks will short out the coil if they make it to the metal part of the coil . If a carbon track is found , it usually can be scraped off with a pocket knife and all should be well .
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08-19-2019, 07:28 PM | #6 |
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Re: Coil failure ?
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After replacing the coil, I am back in business. |
08-19-2019, 08:13 PM | #7 |
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Re: Coil failure ?
Might check the resistance in the primary and secondary windings. Seems like the secondary winding may be the issue. Unless there is a hard failure, coil troubleshooting can be challenging. The number of coils changed is much more than the number of actual failed coils. Let us know what you discover.
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08-19-2019, 08:19 PM | #8 |
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Re: Coil failure ?
1. If the cutout opens, how does generator voltage get to the coil? 2. Isn't generator voltage regulated by the position of the third brush, not the battery?
Last edited by 40 Deluxe; 08-19-2019 at 08:34 PM. |
08-19-2019, 08:46 PM | #9 |
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Re: Coil failure ?
Voltage depends on the volt of the battery that is used . the generator charges in amps and the amount of amps that the generator charges is controlled by the adjustable third brush in the generator . To increase the amount that the generator charges push down on the third brush . to decrease charge , raise the third brush .
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08-19-2019, 09:01 PM | #10 |
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Re: Coil failure ?
The condenser would be the first suspect on my list Those original style condensers are real cheaply made inside take one apart. After taking one apart and seeing how the connections are made and what they are made of I am using only the more expensive short proof condensers . B0B
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08-19-2019, 09:03 PM | #11 |
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Re: Coil failure ?
X2. If I had the condenser and coil biz for Model A owners who changed those parts when they were good, I'd be a rich man.
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08-19-2019, 10:40 PM | #12 |
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Re: Coil failure ?
Mine failed on a rural road in Nevada, 50 miles from nearest house. I let it cool turned it over and drove home. Bought a new coil and have been carrying it around in the car for 2 years but the old one is still working. Old coils are oil cooled and sometimes short-out when pointing down. Good luck
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08-20-2019, 08:12 AM | #13 |
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Re: Coil failure ?
I've had coil failure in cars, but it's rare. My A was running great this summer but started missing and would barely run. Stalled in the driveway so I pushed it in the garage since it would not start again. Swapped the coil out but still nothing. It had a "made in USA" condenser that I had swapped out two years ago from my Dad's stash, so I didn't think it was the culprit, but changed it with a short-proof one from Snyders and engine started right up.
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08-20-2019, 08:40 AM | #14 |
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Re: Coil failure ?
Did you replace the condenser for a reason? I would look at the work you did recently before changing out a part that has been trouble free for 50 years. Those old coils are known to be very reliable.
On a side note, I recently acquired 2 untested original coils. Put them both on the car, both made a nice strong blue spark. Gave one a coat of paint, put it on the car and I swear it runs better than the 30 year old oil filled coil it replaced. |
08-20-2019, 09:55 AM | #15 | |
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Re: Coil failure ?
Quote:
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08-20-2019, 10:46 AM | #16 | |
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Re: Coil failure ?
Quote:
Same experience as in post 14. |
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08-20-2019, 11:00 AM | #17 |
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Re: Coil failure ?
My vote is condenser. or a loose conection.
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08-20-2019, 11:25 AM | #18 |
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Re: Coil failure ?
I purchased a NOS Delco coil for my 50 olds it quit on me after a short while,when the engine rpm went up the engine would start to die,then it left me on the side of the road.The condensers are all original style for the most part,Brattons sells an excellent one.
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08-21-2019, 08:52 PM | #19 |
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Re: Coil failure ?
Update - new coil and condenser installed today, although both removed parts tested OK with my DVM. I have good spark now, and the timing is right on the mark, but the car will still not start. I’m puzzled, as there is plenty of fuel flow to the carburetor. tomorrow, I plan to take the carb off and check it out. The car died suddenly after I had just filled the gas tank to the top and was driving home at 40 mph or so. I would appreciate any bright ideas, as I am puzzled !
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08-21-2019, 08:56 PM | #20 |
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Re: Coil failure ?
Sudden death would usually turn me towards the ignition system. However, gas flow to the carb doesn’t always equate to gas flow out of the carb. Crank it and see if the plugs get wet?
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08-22-2019, 10:36 AM | #21 |
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Re: Coil failure ?
The low priced ignition switches have caused this problem for me in the past .
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08-22-2019, 02:29 PM | #22 | |
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Re: Coil failure ?
Quote:
If your A stops running, and everyone suggests it's the coil or condenser (as they certainly will). So you test them and they test good. DON'T replace them. Continue to diagnose until you find the problem. Replacing parts before the cause of the problem is known just introduces additional variables.
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08-22-2019, 04:14 PM | #23 |
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Re: Coil failure ?
Remove wire lead off spark plug. Place it 1/8 inch or so from the spark plug terminal - ignition on, turn over via starter, should see a nice blue spark across the lead to plug gap. Quick way of telling if you have spark.
Pull plug, smell plug for gas. |
08-23-2019, 09:09 AM | #24 | |
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Re: Coil failure ?
Quote:
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08-23-2019, 10:50 AM | #25 |
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Re: Coil failure ?
Bought a new coil at NAPA. checked for spark, nice blue spark. Pluged i the coil wire it would not start, no spark. The long and short of it is, the coil would not throw a spark when firing under compression. Change out that coil ran fine
Moral the story, Just because it's new don't mean its good. JB
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08-24-2019, 09:37 AM | #26 |
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Re: Coil failure ?
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I've had 2 coils fail on me over the years, not on Model A's. One was a '69 Ford 1/2 ton w/a 302, driving one day and the truck backfired and snorted a couple of times and settled down and ran fine. 2 or 3 years and many miles later it started running not quite right, felt like it was a carburation problem, disassembled, cleaned and checked over the carburetor and all was good. Truck still didn't run quite right. Cleaned and re-gapped spark plugs and truck ran good for a day or 2 and then started acting up again. Talked to an old timer friend and he said "it's your coil". So I replaced the coil and problem solved. The other time a coil failed was on a '89 Ford Bronco w/a 351, it just quit and that was it. I was on my way to work and a work mate stopped and gave me a hand to push the car around the corner onto a side street for later retrieval.
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08-24-2019, 10:03 AM | #27 |
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Re: Coil failure ?
I had a similar problem until I finally replaced the conduit covered wire from the ignition switch to the base of the distributor. My original one had dried out and in many places missing wire insulation and would ground out .
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08-24-2019, 10:09 AM | #28 |
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Re: Coil failure ?
I had a similar problem until I finally replaced the conduit covered wire from the ignition switch to the base of the distributor. My original one not only had dried out insulation but also missing insulation and would ground out.
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08-25-2019, 07:36 PM | #29 |
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Re: Coil failure ?
31Ford - that is exactly what my problem turned out to be...my ignition cable inside the conduit was shorting intermittently.....new cable arrives tomorrow (I hope) - I’ll post an update. For all I know, the original could may be good, in which case I will re-install it and keep the new coil as a spare.
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08-27-2019, 06:41 AM | #30 |
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Re: Coil failure ?
Last post on this - I installed a new ignition cable/conduit yesterday, and immediately had a very strong spark from the coil. The car started right up. In hindsight, I should have gotten my DVM out first thing to troubleshoot the issue - hope I remember this in the future. Anyway, with new points, condenser and coil as well, the car should be good for a while.
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08-28-2019, 12:08 AM | #31 |
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Re: Coil failure ?
I bot a new 6v coil from one of the parts houses couple of years ago..30 model A..car would run fine in my yard but at speed it missed badly so I checked spark at a very fast idle speed !! no spark at speed ,so in the ditch the new coil went and found a old 50's coil works good since..be ware junk products on the market....sc
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