Technical Sideways mounted coil? Measuring Ohms?

Boring details are below, but my basic questions if you don't want to read all that are about will mounting an oil filled coil on it's side make it fail prematurely or function poorly, and how to determine the ohms of a new coil?


I'm having an issue with my T, it starts easy and idles OK but it breaks up badly under load. Hoping to race it in Hillsboro next weekend but this issue is keeping me from it.

Engine is a '38 24 stud, has never been rebuilt as far as I can tell but it doesn't smoke, original intake with a single Stromberg 97 (a rebuilt original one, #45 jet) with an oil bath air cleaner, ignition is a Stromberg E-fire setup bought last year, has the correct resistance style wires and what I believe is the correct 6V 1.5 ohm coil as the manual suggests.

It ran great last year, although it was driven very little. Ran good a few weeks ago when I got it back out, but after driving it a while (not a ton, less than 50 miles I'd guess) the plugs got fouled up black and it started breaking up/popping under load.

Plugs seemed wet, like weak spark or too rich on fuel. I drained out all of the fuel and replaced it (some was old, so I questioned it), I also replaced all of the plugs with new NGK B6L's but no dramatic change. Tried running it with no air cleaner as well, no help. Had the top of the carb off and still looks like new inside, not dirty. Inside of distributor cap looks like new yet.

The coil was mounted sideways, with the positive terminal straight up, which I've read is a bad idea. It didn't leak, and it hasn't failed completely, but it sounds like it's only 2/3 full of oil and the car sure runs like it's got weak spark.

I'd like to try to replace the coil and mount it vertically to see if it makes any difference, the Stromberg manual says it needs to be a 1.5 ohm coil, how do I determine that? How is it measured? I kinda doubt the parts store will have any specs on it. Could a bad coil even cause breaking up under load, or do they typically just fail completely?

I don't want to throw the Stromberg E-fire distributor under the bus just yet, I tried to buy new points for the old helmet style dizzy from multiple vendors and everything I got was junk. I was hoping this would be the fix and it sure starts beautifully now but my issues sure feel ignition-related.

Hoping for some guidance. Be gentle, I'm much more of a bodyman than a mechanic and I get frustrated easily.

 

Check resistance from positive to negative to get your reading .

secondary resistance is positive to coil wire plug.

sounds like bad ignition, I’ve seen coils crap out once heated up.

if it’s low on oil it’ll heat up faster, I know you can ,but I’ve never liked coils mounted on there sides, or upside down. Not supposed to be an issue but don’t make me feel warm n fuzzy

when’s the last time you did a complete tune up ?

just had a unit last week no start, went through the diagnostic everything checked out but no spark out the cap, so dug a little deeper.the rotor looked fine, but had high resistance in the rotor how that even happens is beyond me but a $2.19 rotor and it was up and running !! Oh wait that’s why !!!! A $2.19 rotor

 

Measure ohms across both the primary and the secondary winding.

Coils can sometimes fail in ways that are tough to diagnose. They can show defects when warmed up yet test OK when cold. All it takes is a few shorted windings in the secondary to cause trouble, it will test "in spec" and it would be impossible to find without a scope or substitution. Most of the time though, with engine problems, it ain't the fault of the ignition coil. You might he one of the lucky ones!

 

I’m also interested what someone with “real”knowledge has to say, my coil seem to have shit the bed also. 12 v mounted sideways on top of intake, poles are opposed and on a horizontal plane. Resistor wire off ignition and was functioning as best I could tell at the time, I did get it running again after about an hour, checked all connections, cleaned points and plugs, but ran like crap. BiL brought me another coil, installed, ran kinda shitty for a bit then cleared right up.

 

I understand the test process but what are the parameters for a “ good” 12 v coil with resistor.

 

Well if my ancient Micronta multimeter is correct, my coil gets 1 ohm on the primary circuit (too low for spec on the Stromberg distributor) and just shy of 8000 on the secondary. Not sure what the secondary reading is recommended by Stromberg but I'm certainly going to go to the parts house tomorrow and check a new coil, see what it's got. Maybe this thing did go bad, or is at least out-of-spec for the application I'm using it in.

Thanks Vandenplas and Truck64 for the replies, and Wanderlust I will be sure to report back what I find in case it's helpful. I've read a TON of threads over the past few days and too many get left open-ended without any real resolution to work from.

 

Hard to say any where from .5 to 2500 ohms on the primary
And 5-20,000 kilo ohms on the secondary .

gotta go by what it says in the coil.

general rule of thumb is low resistance on primary and high resistance in secondary , but to pin point and find a fault like @Squablow is looking for you need to know the specs of
Your specific coil.


There are general specs for testing just about anything.

And unfortunately with the cost of common parts now a days some times it’s easier to swap parts then diagnose stuff, but with the quality of parts some times your swapping junk for crap or vise versa

 

sideways mounted coil.....hmmm....seems a lot of 60s cars came with that as original equipment. The only time I've ever had trouble was with a 383 in a slightly off topic car, with over 200k miles on it, there was evidence of oil leaking out the coil, and it died going around corners. New coil fixed it. This was over 40 years ago, so my memory might be flaky.

about 1 ohm resistance sounds right to me.

I'd be looking at other things...but it wouldn't hurt to pop another coil in it just to eliminate that concern.

 

This is a case where someone with an ignition scope could tell you your problem in minutes. If you don't test, you can only guess.

 

YEAH, probably should not mount on side. I don't understand WHY Buick did it for so many [ 20+?] years.

Ben

 

True ignition coils from Bosch are meant to run in any position. The factory German (big dollars) and some Brazilian ones are filled with correct level of oil or the epoxy models can be run in any position. VW's are mounted upside down. Also their resistance is usually on the mark. The other Bosch coils made from other countries are not as good. Went thru this recently. Hope this helps.

 

Setting for a while , wet/ fouled plugs , dirt in needle & seat ? ,internal carb leakage ?

 

I should mention, the coil that was on my car sounds like a half-full can of soup when I shake it. I just grabbed an ancient one off of a '53 Chevy parts car I have in the back yard and it doesn't slosh like that at all. I've handled a lot of coils and never heard one slosh around like that. The old Delco one does however also check out at about 1 ohm primary resistance and 8K secondary, (same as the sloshy one) and the Stromberg manual insists on 1.5 minimum.

 

The car sat for about a year, which is why I suspected old gas, but draining and replacing it did nothing. It did have fouled plugs, I replaced them with new NGK's right after changing the gas but no change. I think the fouled plugs are a symptom and not a cause.

 

I'm trying my best not to just throw parts at this, and the Stromberg people are very specific about the resistance of the wires and coil and stuff this needs to run, so I'm trying to be really thorough. I don't know anyone with an ignition scope, if I'm being honest I don't even know what that is. I'm a body man in over my head here.

 

Ford mounted coils on their side from at least the 50's thru the 70's. I cant imagine they'd do anything that would cause possible mass warranty issues. But....if it sounds like it's low on oil, swapping it for a different one is an easy thing to do. I'm no help on selecting the perfect coil though.

 

I'm diggin' that T.

 

Micronta made some good meters, but they also made some really bad ones so your mileage can vary depending on what you have. Measuring small resistances in the single digit ohm range requires a pretty decent one. A 1.5 ohm coil is fairly typical for an electronic ignition coil although some of the "coil packs" on current engines can be quite a bit lower. A coil used in a points ignition system will be more in the range of 3 to 5 ohms as the current through the points needs to be low enough to keep them from burning up.

The oil in a coil is a dielectric, and helps to insulate the windings from each other. It is possible that if the coil has a low level (either from leaking, or manufactured that way) a portion of the secondary windings could be above the level of the oil and more prone to internal arcing between the windings, or to the iron core of the coil. Trying a different coil is probably a good idea.

The high end of your ranges for both primary and secondary are, um, well, high.

2500 ohm primary?

20,000 Kilohm secondary? That's 20 Megohms.

I don't think you'll see either in an automotive ignition system, although the DMC-12 Time Machine might have had something like that in it.

 

I've mounted them all over the place never had an issue. I never heard any of this until I got on the internet. Maybe I was just lucky, I doubt it...

 

OK, I did some research on this a few years ago when I had a coil go bad on my Model A. On my A, I had the coil mounted up side down with a short coil wire going to the dist. It lasted about two years when the car would not start when hot, after a cool down all was fine again. replaced coil and no problem.
So I wanted to find out if mounting the coil up side down was ok or not. Long story short, there are coils that are designed to be mounted on the side or up-right and I guess up side down. it has to do with where the wire windings are in the coil itself and the amount of oil. If they are more at the top with enough oil to cover them or if the windings are more at the bottom. I would think most universal coils should be mounted up-right so that is what I did and it has been fine for over 3 years now.

 

You want to use 4 wire resistance testing for such low resistance, i.e. the current going through the test subject and the voltage measurment on the test subject is connected by separate wires. That way the resistance in the test wires does not change the result.

There are good meters for this, but you can get it done using the ordinary stuff too. You need a battery (or other current supply), something to limit current to a sensible level, something to measure the current, and something to measure the voltage. If you for example run 1A through the test subject 1V across it would mean 1 ohm. 1 millivolt would mean one milliohm, which is basically nothing, and most multimeters can measure millivolts, so this can be a VERY sensitive method (as long as the test subject can handle a large enough test current).

 

I googled it, yeah, it's an electronic distributor.

I'd use points also. Getting good replacement parts these days can be a problem....and finding good old used parts for stuff that old, is also difficult.

 

Jimmy six and Chevy stovebolts often have coils mounted upside down. Sometimes, plug wire sets for those engines have coil wires so short, it's the only solution.

 

Don't get too hung up on this, your meter is probably not real accurate at 1 - 2 ohms anyway (most aren't). There's little to go wrong in a coil that will result in a loss of.5 ohms resistance in the primary coil. There could be an internal short circuit that eliminates some of the turns of the primary coil, but I think that would be rare. Shorts are more likely to be in the secondary side where the voltage is much higher.

What about the condenser, have you replaced it?

 

I’m using the e fire, as well, with no problems. Not every 6v coil will be the spec stromberg calls for (1.5 ohm). I tested a few cool looking 6v coils, and never found one exactly at 1.5ohm. Eventually went with the pertronix flame thrower. They sell an epoxy filled version in black, and chrome. I would use that, or the Bosch. Electronic ignitions are great when ran as they were intended.

On a side note, I ran an oil filled coil on my model a banger upside down for years without issue. You mileage may vary.

 

I don't think I ever saw one of those old Ford "yellow top" coils that wasn't mounted sideways from the factory, and I've also never had one that didn't still work, or have one leak- pretty good product. I always save them off cores, as guys doing restorations are always looking for them

 

it's electronic.

 

The yellow top Ford coils are epoxy filled.

 

Than it's probably not an ignition problem....