Ignition Coil Mystery!!!

343fireman1 · Post by **343fireman1** » Wed Jul 08, 2009 11:55 am

Alright guys, I'm new to the site, so a little back-story first off. Im a 24yr old Fire/EMS/Law Enforcement student. Im very mechanically inclined and have been working on cars my whole life, but have no formal training. Most importantly, I'm the relatively new owner of a '54 Dodge M37 - quite possibly the coolist thing I've ever seen and had the priveledge of owning!

So here's the problem - After driving my vehicle for approx. 20-30 min, it sputters and stalls as if it were out of gas. It starts back up once, and only once, for only a brief period (maybe 30 sec.), then dies again. Both times this has happened, I empty the 2+ gal. reserve tank of gas I keep in the bed, and try to fire up. It tries to start, just a bit of combustion, then nothing. I try again, the starter motor turns but there's not even the slightest hint of combustion now. On a hunch the first time, I pulled the dist. cover to find my coil damaged. The plastic top had separated from the metal housing of the body. This exact sequence of events has happened twice now, however, the coil suffered the same damage when I left the battery and ign. switches on a couple days after purchasing the vehicle (oops! - never again).

The first time I replaced the coil, my parts guy said that when I left the switches on, I caused a constant current flow through the coil which may have heated it to the point of it's described failure. Although he said that he doesn't think the top should be separating like that. To me it seems reasonable. The heat causes expansion of the fluid inside to the point of release of built up pressure, i.e. the top separating from the body.

What I can't figure is why, under normal driving conditions, does it heat up to the point of failure? I live in Texas, and it's hotter than Hades, but you can't tell me this "tank" can't handle the Texas heat. What's the problem, and what can I do to fix it? Thanks.[/b]

HingsingM37 · Post by **HingsingM37** » Wed Jul 08, 2009 2:28 pm

WELCOME ABOARD

Are you saying the coil separation has happend twice?
It would have to get very hot. Are your cooling lines intact from the air horn to the distributor?
When the engine shuts down is there spark? Condenser is OK?

MSeriesRebuild · Post by **MSeriesRebuild** » Wed Jul 08, 2009 2:48 pm

Check those vent lines, are they in place with the correct fittings installed so that air flow is FORCED through the distributor housing? If they aren't coils will die faster than you can install them. I've had some that cracked as you spoke of, were very old "New Old Stock" & nothing but junk. Is the distributor in good shape otherwise; shaft bushings, rotor, inner cap, etc.? Give me a call if I can help, we'll figure it out. Contact info on website below.

The issue you described sounds like debris may be in the fuel tank & is clogging the fuel lines, Have you checked for rust, etc in your tank?

343fireman1 · Post by **343fireman1** » Wed Jul 08, 2009 11:56 pm

- Coil separation has happened a total of 3 times - once when I left the switches on, then twice while driving. The last two coils failed in the way I described in the post. On both occasions it happened the same way!?
- Cooling lines intact and appear to have stock fittings
- Sparks? - dunno, it starts up for a bit (maybe 30 sec.) then shuts off. Try it again and it wants to start and almost does but then nothing but starter motor
- Dont know how to check proper operation of the condensor, but condensor, rotor, inner cap, all appear to be new
-The previous owner said the tank is relatively new, but the fuel lines have got to be original. I think the sputtering is the point at which the coil begins to fail, bc the vehicle sputters and hesitates then I find the coil separated. The two events have only occured in conjunction.

Think maybe I'll try to remove and clean the cooling lines. There could be debris, maybe some kind of a blockage?
Im thinking - as it appears you guys are - that the coil separation is heat related. Maybe I need a new thermostat? Maybe the old one's rusty and not letting enough coolant pass by? Also, I read that coils can fail bc of bad plug wires or bad plugs. Could eighther one of those cause an impedence in the flow of electricity to the point where the coil heats up?

Post by **Cal_Gary** » Thu Jul 09, 2009 6:01 am

Welcome aboard Fireman1! Always glad to see a younger member enlist, to help rescue these fine machines! I too, have a '54.

Last summer I blew a coil by not having the ballast resistor wired in place-mine was a 12V coil but the symptom you described sounds ominously familiar. I do not know if the 24v includes this item-Charles, Lifer, or some of our other forum members may know.

Anyway, this is THE place for all your M37 questions-glad to have you with us!
Gary

Lifer · Post by **Lifer** » Thu Jul 09, 2009 6:37 am

Okay...I don't know what I can say except that separation is usually a heat-related issue. Any time the ignition switch is turned on, you will have 24 volts running from the battery, 'round and 'round and 'round through the primary windings, to the distributor. This excites a (much) higher voltage in the secondary windings, which provides the spark. If it were just a current flow problem, we'd all cook our coils every time we drove our beasts!

That said, it's either a ventilation problem or a defective coil. I've had no experience with the new replacement coils, but I've seen numerous reports on the forum that they aren't much good. I'd strongly recommend making sure your vent lines are clear and properly aimed. I'd also have any replacement coil tested before installing it.

Charles can give you some expert advice on the matter.

rickv100 · Post by **rickv100** » Thu Jul 09, 2009 7:02 am

343fireman1,

I am facing some problems with a coil myself but not what you are mentioning.

The cooling lines run from each side of the distributor across the block to the elbow connects to your carbureatour. It forces air thorugh the lines to cool the distributor so your thermostat can be eliminated as a possible cause.

Alan Bowes wrote a great article on rebuilding the M37 distributor. He used to have it online and someone may have an archived copy of it. It was also published in Military Vehicles awhile ago.

Rick

MSeriesRebuild · Post by **MSeriesRebuild** » Thu Jul 09, 2009 8:15 am

Can't assume anything, you need to know all is intact, clear, attached with correct fittings for proper air flow, etc. Take it apart & check, there is no other way. The previous owner saying the tank is clean is worth absolutely nothing, check it & the lines, fuel filter, etc. Nobody can tell you what to do sight unseen, you have to start eliminating the issues 1 by 1.

I'd run a compression test on the engine, that could be the issue, electrical problems & fuel flow may not be the issues at all, although cracked coils suggest something in the area of electricals.

I had a truck come in 2 weeks ago, would start up, run until warm & knock off, no more cranking until a day or so later. We ran a compression test at the onset as we generally do if engine issues exist. 40-50 lbs per cylinder was our result. Well that explains it all, no need in addressing outer issues until the engine is rebuilt, it is fruitless.

343fireman1 · Post by **343fireman1** » Fri Jul 10, 2009 1:27 pm

Alright, guess I'm gonna have to stop putting it off. My next day off I'll disassemble, check, clean and re-assemble the cooling lines. I've got a new coil and new plugs ordered (figured it's prob. time anyhow), so I'll install those and post, in about a week, any progress made. I’ll check my compression and post those results as well.

Thanks for all the help so far!

WCarlsrud · Post by **WCarlsrud** » Fri Jul 10, 2009 2:08 pm

You may want to check the air horn between the air filter and the carb. I've got one that is missing the angled tube and the bent tube that go into the airstream inside the air horn. IE look inside the tube where the lines connect to the air horn.

I burnt up a couple coils with that one.

amanco · Post by **amanco** » Mon Jul 20, 2009 6:37 am

My cooling lines are gone. Haven't been there since I have had the truck. Some one at some point in time decided they were not needed.
I want to put them back. What size line and in the previous message what angled tube should I be looking for? One inside the air tube between the air cleaner and carb? Any photos?

MSeriesRebuild · Post by **MSeriesRebuild** » Mon Jul 20, 2009 8:09 am

amanco wrote:My cooling lines are gone. Haven't been there since I have had the truck. Some one at some point in time decided they were not needed.
I want to put them back. What size line and in the previous message what angled tube should I be looking for? One inside the air tube between the air cleaner and carb? Any photos?

The line size is 3/16", the fittings are special to the application, you will have to find originals or make them if yours are missing.

Brett · Post by **Brett** » Mon Jul 20, 2009 6:48 pm

Has anyone got any suggestions on how to make a mil dist. live with a civvy carb setup? I was thinking maybe use the vacuum side of the fuel pump.

Brett

knattrass · Post by **knattrass** » Tue Jul 21, 2009 8:43 am

Ours were trashed, so we went to NAPA and bought a fist full of various length brake lines and BTF (bent-to-fit) following the ones that came off. We replaced all the fittings from ACE Hardware. We ended up using a small piece of copper tube and soldered it into place pointing up stream. We spent about $25 and it all new.

amanco · Post by **amanco** » Thu Jul 23, 2009 9:22 am

Thank you for the photo and other information!!

Ignition Coil Mystery!!!

Ignition Coil Mystery!!!

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