Posted October 23, 2012 - 05:31 PM
Posted October 23, 2012 - 05:39 PM
I'm thinking either you have bad points or a break in the wire. Possible a loss of the ground to the points?
Posted October 23, 2012 - 05:44 PM
Posted October 23, 2012 - 05:53 PM
Posted October 23, 2012 - 06:11 PM
Posted October 23, 2012 - 06:14 PM
Assuming you do have 12 volts at the + side of the coil, check for 12 volts at the - terminal of the coil. If you find 12 volts there, then for the moment, the coil would appear to be OK.
But we need to find that out. So, disconnect whatever it attached to the negative terminal of the coil. You need a piece of wire a couple feet long that will have one end attached to a clean spot on the metal of the engine so that it finds a good, solid ground. Remove the spark plug, attach the plug wire to it and then lay the body of the plug tightly against the engine so that it makes a good ground.
With the keyswitch turned on, take the loose end of that jumper wire you grounded to the block and swipe it past the negative terminal of the coil so that it makes momentary contact. If the coil is working and you grounded the plug properly etc then you should see a spark jump the plug gap.
A nice, fat blue spark says that the coil is good. No spark says that you either did not perform the test correctly or the coil is defective.
Assuming that you do have spark, then you have now isolated the problem to the points and the wire leading from the points to the coil's negative terminal. If this wire has defective insulation or is trapped under the points cover then it may be grounding out, thus rendering the points useless. So check that wire carefully.
this was sent to me from ta
Edited by CASENUT, October 23, 2012 - 06:15 PM.
- KennyP said thank you
Posted October 23, 2012 - 06:43 PM
Test light in the plug wire hole of the coil (when working properly) will blow the test light. I have both the adjustable spark plug test dummy and the inline neon test light. They are cheap and really speed up the troubleshooting on engine problems. $50 now will save you a hell of a lot of time over the life of the test equipment if you are making a hobby out of this, if not auto part stores will loan them for free.
Edited by rat88, October 23, 2012 - 07:02 PM.
Posted October 23, 2012 - 06:53 PM
Posted October 23, 2012 - 06:59 PM
Jim, I will try that. It sounds like a good way to test it!
- CASENUT said thank you
Posted October 23, 2012 - 08:16 PM
if you have 12 volts at pos. terminal of coil the neg. terminal of the coil connects to ground through the points. Points should close at TDC on compression stroke. Boom fire if fuel, spark and compression.
Most automotive coils run on 6V, not 12V - even if the car has a 12V system. There is either a ballast resistor or resistance wire to drop the voltage while the engine is running and there is usually a circuit to deliver full battery voltage to the coil while the engine is cranking over, to provide a hotter spark. Running a 6V coil on 12V will make it heat up and fail prematurely.
Spark is produced when the points open, not close. The collapsing magnetic field in the coil produces the high voltage needed to fire the plug and when the points close the field is renewed for the next time.
Posted October 23, 2012 - 08:28 PM
Coils with internal resistors are a whole different critter. Suffice it to say you'll have 12 at the +, and 0 at the - with the points closed referenced to ground.
Posted October 23, 2012 - 10:12 PM
I remove all wires from the coil
I check the + to - if I get a reading good for now
second: check the + to coil tower - if I get a reading good for now
third : check the - to coil tower - if I get a reading good for now
this tells me that I do not have a short in the coil
then I check the manufacturer's web site for the specs the I model I am testing
if it check close to the model specs the it should be good
if not close to the specs you got a weak coil and you should replace it