Every once and a while there is a question about testing a Ford induction coil.

The advise a majority of the time is to use a HCCT to identify and reset double sparking coils.

The advice is also given not to use a "buzz box" to test coils as all they do is indicate a coil is buzzing, but no value to the health of a coil.

My question is this, when driving a a T that is not missing, how do you know the coils are double sparking when traveling a warp speed of 20 mph and in hyper drive at 30 mph?

My suggestion is that if your car runs smoothly with no detectable miss, especially when pulling a hill or when you first start out or shift to high, leave things alone. However when you test the coils the best test would be on a hand cranked coil tester. you can do a pretty good job on a "buzz box" especially if you connect it to a T running on magneto. You should get a steady spark and fire at about 1.3 amp. Then put your coils in a T and run it around at different speeds and different attempts to accelerate. If it is smooth, go with it.

The Coil tester or electronic coil tester is the best way to test coils and if you are going to just test and adjust coils and keep them for spare or send them to someone else, best way to test them, but NOT the ONLY way to test.
Norm

I use this one from fun projects.

Not as pricey as an HCCT but does a decent job
www.funprojects.com
under the products tab search for CT-1

....and is MUCH lighter to carry!

Coils that double spark can result in poor engine performance, typically at lower engine speed. Here is another way to know for certain a coil is double sparking and how to correct it.



Proper coil adjustment also requires all 4 coils are set for equal firing time which this tester actually measures. The HCCT relies on average coil current of 1.3A as an indirect approximation of firing time. Be very careful to not bump the points during transient an installation, they are more sensitive to missadjustment than many realize.

Much more information is available at: www.modeltecct.com

RE; Be very careful to not bump the points during transient an installation, they are more sensitive to missadjustment than many realize.

That is so true! A little bump can change for great to bad real fast.

Not a problem for those with the gift of being able to tune a coil by ear.

PS, how do you do that rolly eyes thing?

Here's how a double spark looks on an HCCT.

Let me re-phase the question.

On the forum the question about double sparking has been asked. The implication appears to be the double sparking of a coil can be an issue to the performance and operation of the Model T, or similar car using the induction coil as part of the ignition system.

1. At normal driving speed in a Model T - 25 mph for example - how can one determine that the coils while in the car are double sparking?

2. When starting a Model T Ford -- either with the battery and starter, with the battery and crank, magneto and starter, or with the magneto and hand crank for starting.. how does one determine that there is double spark occurring?

3. When is the double sparking a determent to the starting or operating of the car in normal driving conditions?

The introduction of using a HCCT or a electronic tester is with the coil off the car, then the double sparking is part of a discussion. But only when the coil is on the test bench it is pointed out that double sparking is occurring.

Don't know of any way to check for 'double spark' without a HCCT, or modern Strobo or newest ECCT.

What you can expect with a 'double spark' coil when running is lost of power.

Had experience once with the '24, trailered it to brother's house, and fired up, ran good. Then loaded 4 folks in the T for a cruise up his driveway and out, but the T just struggled to reach the top.

Did the screwdriver to plug test, and all were firing. But still ran poor when climbing with 4 aboard. Later ran more by myself on flat, and T seemed OK then.

Back home pulled the coils and put on the HCCT, and low and behold, one was double sparking bad.

So, you can suspect double spark as cause, if you notice poor performance occurring. Sometimes you need a hill to give a load to the T, that will stress coils, plugs, and other parts too Including the driver!


My home made 'Buzzer Box' for testing, has amp gage and plug to check for sparking at the plug.



Seems OK, the coil can spark a plug



Then put that 'good' coil on my assembled HCCT, and you can see things you can't on the buzz box.



At some points on the magneto plate, appears good sparking,.....



....until you see this !

Hold a spark plug lead near the fan, works better if you make an arched piece of wire. Poor mans road side coil tester.

George. Double sparking leads to a loss of available voltage. At idle or even light cruise you may only need 5-6 kv to fire the plug. This can be supplied by a double sparking coil. When accelerating or pulling a load or hill the kv requirement raises and you may require 15-20 kv or more. The double spark shares the available voltage and can't meet these requirements resulting in misfire. The only reliable way to test is on a coil tester. A buzz box won't reveal a double spark but you may notice an erratic spark at the gap.

Andy

Found this reference to sparking in a 1921 Motor magazine.

The discussion on sparking had to do with coil points.

The article stated that sparking (not clear if was also related to double sparking, the article did reference adjusting the points/coil on a HCCT) may be related to:

1. an exceptionally strong magneto.
2. to stiff an adjustment to the vibrator springs.
3. too wide a sparking plug gap.

So one thing that may still be possible even after using a HCCT to adjust the coils, the double sparking can still occur whilst driving if the vehicle's magneto is producing a higher output (current, not voltage?) than the HCCT (and even the modern electronic tester.)

https://books.google.com/books?id=VT0fAQAAMAAJ&pg=RA2-PA34&dq=double+sparking+fo rd&hl=en&sa=X&ved=0ahUKEwjW6OCaoaXXAhWJ4iYKHfa_Cms4ChDoAQglMAA#v=onepage&q&f=fal se

Kep, now that makes sense, I'll have to try it. Dave in Bellingham,WA