how to test coil (coil hot)

mas00 · Posted: Mon Apr 09, 2018 2:31 pm Post subject: how to test coil (coil hot)

So I have done a top build of my vw 1500cc and I am trying to test the engine. While the ignition turns it back fired and the coil ran very hot. I test the + and - and got 3.5 ohms, but when I tried to test the coil wire and got no reading.

Does anyone know how to test the coil or possibly other wires to see what is wrong or is my coil just bad? Thanks in advance. Mas

mukluk · Posted: Mon Apr 09, 2018 3:23 pm Post subject: Re: how to test coil (coil hot)

It's normal for the coil to heat up with the ignition on and the engine not running.

Testing the primary is like you did, measure from the positive to negative posts. The secondary is checked by measuring from the positive to where the coil lead plugs in -- normal reading will be in the 10k ohms area. Don't leave the coil to distributor lead installed when checking the secondary as that will skew the results.

If you're not getting a spark from the coil lead, the lead itself might be bad. Try plugging a spark plug lead directly into the coil instead to see if you get a spark that way.
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tasb · Posted: Mon Apr 09, 2018 6:44 pm Post subject: Re: how to test coil (coil hot)

Here's an illustration that I like.

Image may have been reduced in size. Click image to view fullscreen.

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Wayne S. Johnson · Posted: Mon Apr 09, 2018 6:48 pm Post subject: Re: how to test coil (coil hot)

I set dwell on the bunch with a hand drill taped the distributor shaft. The same setup could be used with a coil, the length of the spark is proportional the output voltage. Not sure exactly what is normal, but about 1/2" should be good.

My CD ignition makes a 2" spark, I don't need a high voltage wire for testing because the spark jumps out of the coil and down the side.
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mas00 · Posted: Tue Apr 10, 2018 7:11 pm Post subject: Re: how to test coil (coil hot)

thanks, coil was bad so I had to get a new one

tasb · Posted: Tue Apr 10, 2018 9:56 pm Post subject: Re: how to test coil (coil hot)

some would tell you to find a genuine German Bosch (old) rather than brand new.
_________________
Roads Scholar
1957 Kombi low mileage 36 hp governor equipped M 178 Slow Drag Winner 2014, 2015, 2018

1965 hardtop Deluxe Microbus owned since 1990 M 620 factory 12 v 1500cc

1961 (October)Single Cab- Road Trip Workhorse

Member# 2059


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