Old School Ignition Coil Problems


$100 site donor 2023
Feb 19, 2013
Phoenix, AZ
Having some issues with the ignition coil on my sand rail with a built 2234cc VW turbo air-cooled engine. Has an 009 distributor and electronic ignition. I brought it back from a trip to the dunes and it wouldn't start when trying to pull it off the trailer. Would sputter a little bit but would not run. My aunt has a '70 Beetle (1500 SP) and I went and pulled the ignition coil from it, hooked it up, and it fired right up. That coil is looking pretty old so I decided to buy 2 coils from the local VW shop, some blue Beru ZS172 ignition coils.

I've tried both Beru coils and I can barely get it to start, and it'll only run with throttle. Not very well. I can put the coil on every time from the '70 Beetle and it runs just fine. I actually was able to put the original coil back on and get it to run now, but it doesn't seem it runs as well as with the borrowed coil.

I put a Beru coil in the '70 Beetle and it seems to run fine, I haven't driven it yet though.

Any ideas? I'm very new to this sort of stuff.

In the pics, from left to right is Original Bosch coil, borrowed unknown coil, and then Beru coil. From left to right, the ohms from the +/- terminals is 3.6, 1.8, and 3.7.

The original is a Bosch 9220081083 K12V. Was painted purple years ago to match the car.

I would be curious what the resistance of the primary and secondary windings of each coil would be.
In the pics, from left to right is Original Bosch coil, borrowed unknown coil, and then Beru coil. From left to right, the ohms from the +/- terminals is 3.6, 1.8, and 3.7.

No surprise that the the coil with 1.8 ohms works the best,

Spark energy is proportional to the primary current squared times half the inductance

With approx double the primary current the 1.8 ohm coil may have near 4 times the spark energy.

Having said all that, while the stronger coil works I suspect it's greater spark energy is simply masking another fault. I would be suspecting the ignition leads particularly the one from the coil to the distributor or the rotor in the distributor.
Is there a ballast resistor in the car? It would be in series from the ignition switch to the + primary side of the coil. The newer coils are usually self-ballasted and should not have a resistor in the car.
What resistance is required by the electronic ignition? Most require an internally ballasted coil, but some can use a non resistor coil.

That said, as barryh noted, I would guess there is another or several other issues. I would look at the HT leads and the ignition feed to the coil including the switch, as well as the feed to the module and all grounds. Check the module itself. Do you maybe have a resistor wire? If so, those can cause problems with age.

I have not had a Bosch coil fail and find the vintage ones are very durable, however your sand rail is probably the definition of severe use so anything is possible.
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as mentioned above, the high tension wires and rotor in the distributor should be considered. Also consider the distributor cap itself. Years ago, I was at my favorite VW supplier store when a VW classic aircooled Beetle pulled up. It was running poorly. The store mechanic took one look, and replaced the aftermarket yellow transparent distributor cap the owner had in it, with a stock bakelite unit. Problem solved.
The distributor rotor on a VW has a resistance unit in it. Yours may be open and it takes the lower resistance coil to jump the spark over from center to rotating tip.
Not a bad idea. Try swapping the rotor from the other VW and see if that helps (assuming its the same).
It's stored at my aunt's house, I'll see if I can go over tomorrow, I'm really new to this stuff so I'm not sure how to tell which is which. I do have this picture with the borrowed coil just sitting there.

AC VDubs are COOL + its amazing the amount of parts available for them as they are quite popular for "buggys" for their low cost + simplicity! hope you get it sorted out!!
If I were you, I'll check the air gap with a feeler gauge between ignition contact points or the igniter to see if it's within specs. It happened once, my Isuzu P/Up's engine suddenly stopped. I'm glad I had an extra new ignition coil. Glad I made it home. The next day, it will not start, again bad ignition coil. I checked the distributor's igniter and it was way off. Corrected the gap into spec and bought 2 more ignition coils, (one extra just in case the one installed fails) and the problem never came back to this day.
When I was a teenager a friend took me for a ride on a Sunday afternoon in his old (new to him) Chevy. A few miles from town the car quit. It would run but as soon as you tried to go more than a few miles per hour it would die - a classic bad coil. His dad was a mechanic and brought us a new (but used) coil. It still wouldn't run properly.

The second coil was bad too.
Just turn the key on and tell us the volts. Yes positive side
12.75v with key on. 9.8v while cranking. That’s at the positive wire to the coil.

The ‘70 Beetle is 12.0v with the key on and closer to 6.0v while cranking. Battery is 12.6v though.

Distributor cap, rotor, and wiring seem ok to me.

your last picture shows what I believe to be a hall sensor that replaces conventional ignition contact points. Your picture before that shows an rpm rev limiter rotor. Either one can fail. Try replacing the rotor with an ordinary one sans a built-in resistor. Amazon has a lot in stock, for example:

there's a lot of info on air cooled vw bugs in many forums out there, thesamba.com is one of them