No spark from coil

[ejay]

My engine issues persist, and this is the latest chapter. Upon turning the key this past weekend, the A4 would not get going. So I dutifully pulled up the unexpected shut down video on youtube and went through the list, again.

I have no spark from the central distributor wire to the block. None at all. I have done this in the past (not my first rodeo) and I had some spark, although not strong. At one point in time I actually bought a new coil from auto store and the spark was really strong! However I convinced myself the old coil was fine with a weak spark, so I did not replace it. Of note is the fact that I have not measured the resistance or amperage on the coil, yet.

My questions:

1-Does a weak spark indicate a weak coil?
2-Does the absence of any spark indicate a dead coil?
3-Should I get a moyer marine coil, or a different brand from an auto store?

As always, I look forward to the education. Thanks!

ej
78 C30

[Dave Neptune]

#1~~~Yes a week coil or a week signal or poor connection or all 3.

#2~~~Yes it could or a "bad" connection.

#3~~~It is a good idea to go with the WWI supplied coil as it will be correct and supports our host and this site.

Do you have points? If so clean with a point file or emery board.

Check for voltage at the positive coil connection with the key on and remember to shut off the key so you don't fry the coil.

Be sure all connections are clean and good and snug!

You can try your extra coil and if it works then be sure of resistance in case you have an EI. For good confidence get one from our host and keep the extra for emergencies or testing.

Dave Neptune

[ejay]

I hate to admit this fact, but there has been more than one occasion where the key was left in the "on" position, without the engine running. I noticed that the coil got very hot, which could represent "frying"?

[Dave Neptune]

Absolutely, it is a common mistake when sorting out trouble to leave the key on. The overheating will cause a winding to "open" leading to full failure. When cooled back down they can work again until the winding opens up again, then no spark.

With the info so far I would say install the extra coil and if she fires up call MMI for the proper coil.

Dave Neptune

[joe_db]

Leaving the key on can also damage the points. They need checking too.
As for the coil, Moyer sells the correct one. Most auto shops have no clue what you need.
I am a bit lucky living on an island, the auto parts guy knows Atomic 4s and will grab the right coil, 99% of shops will not.

[alcodiesel]

Admittedly I am slow on the uptake but I just discovered another reason for a low oil pressure alarm. It will honk, not if, but when I leave the key "on."

[pknier]

Eliminate the possibility the switch is faulty...I had the similar problem and chased everything for days and it turned out to be the switch that would turn the starter, but not make connection to coil/distributor while and upon release. Replaced switch and she roared to life...

[Al Schober]

Spark ignition using points & condenser is a strange beast.
The coil is a transformer and generates the high voltage. The low voltage winding of the coil is connected to the + and - terminals. The high voltage winding goes to the terminal on the top and the - terminal. It does NOT go to the case of the coil. So ask yourself - how does the spark energy get from the spark plug back to the - terminal? The answer is: Through the condenser! It can't go through the points as the points are open.
Please don't ask me to explain electronic ignition.

[ejay]

Does anyone use the male-female electrical connections that attach to +/- posts on the coil? I had those on my old VW bug, which made connecting and disconnecting wires easier.

[ndutton]

Originally Posted by ejay

Does anyone use the male-female electrical connections that attach to +/- posts on the coil? I had those on my old VW bug, which made connecting and disconnecting wires easier.

They're bad form in the marine environment. Closed, captive ring terminals fastened under threaded hex nuts are preferred. Strive for reliability.

[joe_db]

Originally Posted by Al Schober

Spark ignition using points & condenser is a strange beast.
The coil is a transformer and generates the high voltage. The low voltage winding of the coil is connected to the + and - terminals. The high voltage winding goes to the terminal on the top and the - terminal. It does NOT go to the case of the coil. So ask yourself - how does the spark energy get from the spark plug back to the - terminal? The answer is: Through the condenser! It can't go through the points as the points are open.
Please don't ask me to explain electronic ignition.

There are two kinds:
One acts as electronic points. The functionality is the same as mechanical points. They tend to burn out coils, they are "better" than moving metal around and can give you longer dwell. This is great for high RPM hotrods and terrible for a low RPM boat engine. There is a lot in the A4 archives about this and discovering the correct resistance for coils.
Next up is adaptive dwell, this system is also "electronic points" but changes the dwell on the fly to be kinder to coils.
Lastly are the variations on capacitive discharge, aka CD, ignitions. They work like a camera flash, the energy is not stored in the coils it is stored in capacitors that discharge into the coil.

Here is a scope photo from connecting it to my coil:

The big oscillations are the coil firing and the little one is the points closing again.

[Sam]

Joe _ would you have any information on which brand of EI for an A4 distributor would pertain to a particular design that you mentioned. I too get confused explaining electronic ignition other than recommending buying from Moyer. Thx

[joe_db]

The Moyer version is Pertronix, which is a simple points replacement. It will burn out coils picked at random, thus the Moyer brand coil that works with it.
The Indigo ignition is an adaptation of a Crane system that uses an optical trigger. The cheaper one is likewise a simple points replacement and has the same coil issues. Their more expensive system has adaptive dwell.
There are no "Atomic 4" CD systems, but you can certainly adapt one that is sold for car use. Our engines are not demanding enough nor high RPM enough to bother with this IMHO.

[sastanley]

Originally Posted by joe_db

Leaving the key on can also damage the points. They need checking too.
As for the coil, Moyer sells the correct one. Most auto shops have no clue what you need.
I am a bit lucky living on an island, the auto parts guy knows Atomic 4s and will grab the right coil, 99% of shops will not.

We are pretty lucky here too. I took my alternator in for a rebuild to the local Mennonites, and the guy recognized it as from an A4 by the paint color..I knew I was in the right place..their shop is the one that recommended an adjustable regulator.