| Dustbowl | -- 02-10-2011 @ 5:53 PM |
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See my topic "Stops Going Uphill" yesterday. Thanks for many thoughtful suggestions. DK states that he measures 4.2 volts in ignition wire to the coil. In mine, I get only 2.7v when the resistor is cold, dropping to 1.6v after one minute as resistor heats up. (this is without motor running). This seems low; am I correct?
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| drkbp | -- 02-11-2011 @ 11:07 AM |
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Yes, that's too low. You are looking for 4 volts or a little more. Change the resistor. Like they have said on the other string, running 6 volts to the coil will shorten coil life. Are you getting 6 volts to the coil? This can be complicated by using too small battery cables (12 volt cables are too small), probably dropping the voltage lower when you start. When it starts it should jump up though. Ken
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| supereal | -- 02-11-2011 @ 12:23 PM |
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When the distributor points are open, you should read battery voltage, about 6-7 volts, at the coil input terminal. When the points are closed, the voltage at the coil should read about 3.5 volts. You can't check those voltages with the engine running, as you are seeing the "RMS" (root mean square) of the wave form. The purpose of the ignition resistor is to keep the input to the coil stable as the system voltage rises with engine speed. As voltage increases, the resistor heats up, increasing the resistance which, in turn, lowers the voltage thru the resistor. The size of the battery cables doesn't affect the ignition voltage unless the battery is dying, or a poor connection exists. Be sure that the battery ground strap to the engine is present, and the connections are clean and tight. Poor grounds are the major cause of electrical problems in vehicles.
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| TomO | -- 02-12-2011 @ 7:42 AM |
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In addition to the resistor, your ignition switch could be putting resistance in the circuit. Check the voltage at the yellow wire on the switch and then on the black and red wire to the resistor. You should read full battery voltage at these points. In most cases you can disassemble the switch and clean the contacts and brush. You can also get reproductions of the brush and switch plate if the switch plate or brush are severely worn. It helps continuity if you continue on the same post by clicking on the REPLY box, instead of starting a new post every time you want to update the problem. Tom This message was edited by TomO on 2-12-11 @ 7:44 AM
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| supereal | -- 02-12-2011 @ 11:04 AM |
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As usual, I agree with TomO, with one word of caution. Until you locate the source of a problem, don't disturb the circuit. This usually results in either masking the real fault, or inducing an additional problem. To test for bad connections, place the leads of your voltmeter across the ends of each part. The reading of the meter will show you the amount of voltage lost in that leg of the wiring. As it is put in one of Henry Ford's "Fordisms" tucked into the service bulletins, "Diagnose, Don't Guess".
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