Quote:
Originally Posted by ford38v8
Harylufa, To "test the coil heat", the next time your engine fails, pull a plug wire and hold it to a head stud to test spark while you crank it over. A good coil will deliver a strong blue spark about 1/2" long. A weak coil will show a smaller orange spark or none at all. This same weak coil may show strong when it is cool again.
|
If you get a spark from that test then you know you have spark and that the coil, condenser, points, and wires all work. If you don't get a spark, however, that can be because any one of those things has failed and you will only know be testing each one individually as follows:
To truly test the coil to see if it is the problem it must be isolated from all other components that make it fire. To do that, I always carry a spare high tension coil to distributor wire (the one that looks like a short spark plug wire). Then I unplug the fat wire from the bottom or end of the coil and plug the test one in. Then, crank the engine while holding the end of that test wire close to a head bolt. If it fires then when it didn't through the spark plug wire then you know that the spark is stopping somewhere between the coil and the spark plug and isn't a problem with the coil. It could be the short fat wire from the coil to the distributor, the distributor rotor, the distributor cap, or, most likely, the spark plug wire. If the coil still won't fire I then isolate the coil from any problems with the points or condenser by disconnecting the small wire from the top of the coil that goes to the distributor. I then connect a jumper wire from ground that I'll use for this test. Then, with the end of the short fat test wire near a head bolt and the ignition turned on I intermittently tap the small grounded jumper wire on the terminal that I took the other wire off of. That creates the same on/off switching that the points do. If I now get a spark I know it's the points and/or condenser. If I still don't get a spark (and I'm sure power is getting to the coil from the ignition switch) that only leaves the coil as the problem.
I tell you all of this because in the past I too many times jumped to the erroneous conclusion that my ignition problem was a coil problem and replaced the coil without fixing the problem that has always turned out to be something else.
Hope this helps.