TheSamba.com :: View topic - how do you test a coil with a multi meter?

Wed May 19, 2010 6:17 pm

title says it all

Wed May 19, 2010 7:19 pm

my man,set it to ohms. better yet hook a test light to your coils hot terminal from the ignition,make it so they are both hooked up. When the bus dies,does the light go out?

Wed May 19, 2010 7:26 pm

it dies only when driving. it will idle all day.

Wed May 19, 2010 7:32 pm

Alright now we are getting somewhere,does it sputter than die,can you keep your foot in it to keep it going? If it just quits with lights in the dash,right away,you are losing spark.

Wed May 19, 2010 7:38 pm

yes yes yes

Wed May 19, 2010 8:23 pm

You just made me think of something.. I was following your other thread... My coil usta get so f'n hot it would burn your hand. It was a silver one. I put on a blue one and never had a problem.. Same thing, My thing would run for about 5 minutes then die, not to start again for about 30 minutes...

Wed May 19, 2010 11:10 pm

In my thread in the other post, I mentioned that you should check the carburetor's electro-magnetic cutoff valve. A bad one will make the engine do what it has been doing. Did you check it?

Thu May 20, 2010 3:32 am

from aircooled.net:

To check your existing coil, first make sure you have 12V going to the terminal 15 on the coil (Terminal 15 is positive, terminal 1 is negative (think of 1 sideways being negative). If you do, then pull the wire out of the center of the distributor with a rubber handled pair of pliers, and hold it about 1/4" from the metal clips that holds the distributor cap on. Have someone crank over the engine, and there should be a nice blue spark that goes from the end of the wire you pulled out of the center of the cap to the metal clip. It should look and sound strong, and should be easy to see, even in daylight. If it looks thin and weak (yellow is weak, blue is strong), then the coil windings may be giving out. Another test for the Bosch Blue coil, is to use an Ohmmeter and with all the wires taken off the terminals of the coil attach the positive and negative, red and black, wires of the meter to first the terminal 1 and 15 that are printed (stamped) on the coil. You should have a reading of at least 3-4.5 ohms, which is the resistance reading inside the coil. A bad coil will show a higher reading then 3-4.5, you want less resistance. Next, place the red or black lead from the meter to the center of the coil (secondary post), and to either one of the terminals, again 1 or 15 on the coil. You want 9500-10000 Ohms, sometimes you'll see less, but you don't want to see something like 11,000. Or if you have no reading in either case, the coil is trash.

there is also a good post in ratwell's website:
http://www.ratwell.com/technical/BlueCoil.html

Sat Jun 19, 2010 11:09 am

I tested my coil today using a multimeter (ohms), and across terminal 1# and 15# I got 2.8 ohms which seems ok, but from the centre of the coil to terminal 1# or 15# I only got 5300 ohms.

Does this indicate a broken/failing coil ?

Sat Jun 19, 2010 2:31 pm

Spend the 30 bucks or so and buy an new coil. If it fixes it, you are done. If not, at least you have a new coil and one less thing to worry about.

Sat Jun 19, 2010 2:43 pm

Xavi, wow that is a great site I often had coil questions, will this info be for all vehicle coils?

xavi_242 wrote: from aircooled.net:

To check your existing coil, first make sure you have 12V going to the terminal 15 on the coil (Terminal 15 is positive, terminal 1 is negative (think of 1 sideways being negative). If you do, then pull the wire out of the center of the distributor with a rubber handled pair of pliers, and hold it about 1/4" from the metal clips that holds the distributor cap on. Have someone crank over the engine, and there should be a nice blue spark that goes from the end of the wire you pulled out of the center of the cap to the metal clip. It should look and sound strong, and should be easy to see, even in daylight. If it looks thin and weak (yellow is weak, blue is strong), then the coil windings may be giving out. Another test for the Bosch Blue coil, is to use an Ohmmeter and with all the wires taken off the terminals of the coil attach the positive and negative, red and black, wires of the meter to first the terminal 1 and 15 that are printed (stamped) on the coil. You should have a reading of at least 3-4.5 ohms, which is the resistance reading inside the coil. A bad coil will show a higher reading then 3-4.5, you want less resistance. Next, place the red or black lead from the meter to the center of the coil (secondary post), and to either one of the terminals, again 1 or 15 on the coil. You want 9500-10000 Ohms, sometimes you'll see less, but you don't want to see something like 11,000. Or if you have no reading in either case, the coil is trash.

there is also a good post in ratwell's website:
http://www.ratwell.com/technical/BlueCoil.html

Tue Jun 22, 2010 12:05 pm

is 7500 ohms too few? also, with the battery hooked up, I'm only getting a reading of about 10.3V at the positive post of the coil...meaning? battery's at about 12.75-13V

Tue Jun 22, 2010 12:44 pm

Emeritusx wrote: My thing would run for about 5 minutes then die, not to start again for about 30 minutes...

Sounds like a serious problem, you may want to have that looked at. :lol:

Mon Jul 12, 2010 11:01 pm

Buy a coil and keep it in the plastic and just hook up the wires like usual. If it works, mount it up. If it doesn't, return it and say you found a loose wire before ever testing it. Works every time, 60% of the time...lol. My main lead from the coil to distributor went out recently, so when I went to test the coils spark by grounding, I had nothing. Tried 2 coils before I realized it was the lead itself...