Ignition coil problems

Tech questions that don't fit above forums

Moderator: Team

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Ignition coil problems

Post by Truckedup » Sun Apr 07, 2013 5:23 pm

This is a recent problem on my 47 Willys Jeep.I replaced the flat head four with a Chevy 153 engine last fall.. The old flattie had 12 volt system and I used the battery, alternator and coil from the old engine and swapped it on the 153. Points ignition has a ballast resistor. The battery voltage running is 14.5.
Went to go for a ride and it dies....The ignition coil was faulty ,primary shorted to ground...So I put on a brand new supposedly made in USA Crane coil.1.5 ohm coil with 1.8 ohm resistor just like it should be .The Crane coil lasts 10 minutes....Bench test show ohm readings are ok...I substitute a rusty old Delco coil and it starts right up.Put the Crane coil back on...won't start.
So I leave on the old Delco coil.And you guessed it,conked out on the road. Substituted yet another old coil and the engine fires right up..... What the hell is going on here???
Cliff notes,the battery voltage is a steady 14.5..........1.8 ohm ballast resistor....coils used are all around 1.5-1.7 ohms..Newer spark plugs with Packard 440 wire..Vehicle wiring is in excellent condition.
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

Warpspeed
Guru
Guru
Posts: 1249
Joined: Fri Nov 17, 2006 4:10 pm

Re: Ignition coil problems

Post by Warpspeed » Sun Apr 07, 2013 6:36 pm

From the way you tell this, there appears to be nothing wrong with the setup, just some faulty coils and sheer bad luck.
I guess kind of like getting three punctures on the same day.

If the coils were actually burned up and too hot to touch when they failed, that would be a very different matter. But a short to ground or an open circuit winding (without first cooking the coil) sounds more like a like random failure.

If the coils are overheating, it could be that the ballast resistor is not being switched into the circuit when you turn the ignition key from "start" to "run".
Is that a possibility ?
Last edited by Warpspeed on Sun Apr 07, 2013 6:44 pm, edited 1 time in total.
Cheers, Tony.

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Sun Apr 07, 2013 6:39 pm

The coils were not getting hot at all.
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

User avatar
af2
Guru
Guru
Posts: 6091
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Ignition coil problems

Post by af2 » Sun Apr 07, 2013 7:31 pm

What is the primary voltage when you get one to run?
GURU is only a name.
Adam

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Sun Apr 07, 2013 8:05 pm

af2 wrote:What is the primary voltage when you get one to run?
Using a Fluke digital meter is around 12 fluctuating volts. At the same time the system voltage is 14.5. Generally the voltage through the resistor is is around 9 on other engines I have checked.
I tried two different resistors and they were the same voltage.They show 1.8 ohms .... I have never seen a ballast putting out too much voltage,only no voltage...
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

Warpspeed
Guru
Guru
Posts: 1249
Joined: Fri Nov 17, 2006 4:10 pm

Re: Ignition coil problems

Post by Warpspeed » Sun Apr 07, 2013 11:14 pm

Truckedup wrote:
af2 wrote:What is the primary voltage when you get one to run?
Using a Fluke digital meter is around 12 fluctuating volts.
That is your problem right there.
If the ballast is 1.8 ohms, and the coil about 1.6 ohms, there should be less than half the total voltage across the coil.
There should be more voltage drop across the ballast than the coil.

With 14.5 volts, there should be about 6.8 volts across the coil with the points closed, and zero volts across the coil with the points open.

What you actually measure will depend on the dwell angle of the points, but it should be even less than 6.8 volts with the engine running.
As you are seeing 12 volts, I suspect the ballast is not reducing the voltage to the coil as it should.

Check the voltage drop across the ballast with the engine running, I suspect you will measure little or no voltage drop. Either the ballast is incorrectly wired to the ignition switch, or the ignition switch contacts are stuffed.
Cheers, Tony.

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Mon Apr 08, 2013 5:54 am

Yes,the voltage is high,but why? Several different coils and ballasts it's still high.And the meter test ok.
But higher voltage won't ruin a coil.My actual experience with using a typical 1.5 ohm points coil with a Multi Spark CD box. The box feeds 400 volts to the coil primary...The coil lasted for several years and was replaced not because of failure.
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

User avatar
af2
Guru
Guru
Posts: 6091
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Ignition coil problems

Post by af2 » Mon Apr 08, 2013 4:22 pm

Truckedup wrote:Yes,the voltage is high
But higher voltage won't ruin a coil.
Yes it will and that was the point.
GURU is only a name.
Adam

Warpspeed
Guru
Guru
Posts: 1249
Joined: Fri Nov 17, 2006 4:10 pm

Re: Ignition coil problems

Post by Warpspeed » Mon Apr 08, 2013 4:58 pm

af2 wrote: Yes it will and that was the point.
+1
Cheers, Tony.

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Mon Apr 08, 2013 5:07 pm

Warpspeed wrote:
af2 wrote: Yes it will and that was the point.
+1
High voltage will ruin the coil? Go back up and read what i said about using points coils with CD boxes.
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

Warpspeed
Guru
Guru
Posts: 1249
Joined: Fri Nov 17, 2006 4:10 pm

Re: Ignition coil problems

Post by Warpspeed » Mon Apr 08, 2013 5:29 pm

CD boxes discharge a high voltage capacitor into the coil primary.
The peak voltage is very high, but it is only there for a very few milliseconds which is not enough to heat up the windings.

Connecting twelve volts across a coil designed for only six volts will cause twice the current to flow.
Twice the voltage, and twice the current equals four times the power, which causes four times the temperature rise of the ignition coil ABOVE whatever the under hood temperature is..

We can only offer advice. In the end it is your car, and your problem.
Cheers, Tony.

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Mon Apr 08, 2013 6:36 pm

Ok,back on topic. I have tried several new ballast resistors of around 1.8 ohms.I have checked the resistor ohms before and after the engine has been running.Several different coils of .1.5 ohms.All the set ups have 3.5 or so ohms as measured my a Fluke meter.With the engine running at idle the positive side of the coil shows 10 volts at idle,increases to 12.5 volts with more RPM.The other side of the coil connected to the points is about 7.5 volts. The vehicle system voltage is a steady 14.5 volts at any rpm.This Chevy 153 engine runs very well.....until the coil craps out...... What is causing the high voltage at the coil? Everyone is saying the 12 volts will ruin the coil very quickly. Various catalogs list the same ignition resistors for 4,6,and 8 cylinder engines.
And...when the coils fail they are not hot,in fact they are just warm.not even as hot as the engine ..................
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Mon Apr 08, 2013 7:08 pm

And now this, I just went out and swapped the wires onto the coil that failed on the road.Jumped in the Jeep and it started instantly.This was the coil on the engine when is gave a big backfire and stalled out yesterday .There was voltage to coil at that time but no spark.It was only driven 2 miles.. I walked back home and then drove back with another coil. Tried to start the Jeep,no go.So I swapped out the coil,started instantly and ran fine for two miles back home.Nothing was disturbed but the coil wires.
Ohm readings on the coils are normal after a stall and no restart.
So this coil comes back to life....There's always power to the coil,the coil is not getting warm,the engine backfires or misses briefly before stalling out.It's happens three times and each time a substitute coil starts the engine.I rewired the Jeep last year so there's no weird gadgets under the dash killing the power.
Did I mention the condenser was changed and made no difference ....... The points are look normal.................Maybe something goofy with the points????? Maybe I'm looking in the wrong place?
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

User avatar
af2
Guru
Guru
Posts: 6091
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Ignition coil problems

Post by af2 » Mon Apr 08, 2013 7:14 pm

Do you have the start wire hooked up through the starter?
If so unhook and try your readings again.
GURU is only a name.
Adam

Truckedup
Guru
Guru
Posts: 1346
Joined: Mon Jan 21, 2013 2:41 pm

Re: Ignition coil problems

Post by Truckedup » Tue Apr 09, 2013 6:13 am

af2 wrote:Do you have the start wire hooked up through the starter?
If so unhook and try your readings again.
Yes,and it's been checked ,unhooked and no difference I removed the points and they look ok,made sure the plate the points screw to is grounded.
Naked frame LSR bikes, dressed in animal hides clinging to machines propelled by fire...

Post Reply