Voltage at coil?
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Voltage at coil?
Ok my son's truck was iding in the driveway Sat morning, warming up. 80 f-100 with a 302 auto. It started to idle rough and then died, like it ran out of fuel. Check and I've got fuel but no spark. I've got with the key on 2.6-2.7 volts at the lead wires going to the coil. I don't have any spark coming out of the coil though. Is this the right voltage or do I need to check else where? If so then what? Thanks, Texcan
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Joined: May 2007
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From: Solon, Ohio
I don't know on that particular truck, but Ford used to run 8 volt coils with a dropping resistor in series with the 12 volt supply voltage to provide the 8 volts run current.
They had special solenoids that jumped over the resistor during cranking to provide full battery voltage to the coil during cranking. This was done to make up for the loaded down battery which dropped below 12 volts during cranking.
If you have that setup, you would have less than 12 volts to the coil, but it should be around 8 volts I believe.
If that is the case, and that resistor is bad, the truck should still start and run till you let off the starter.
They had special solenoids that jumped over the resistor during cranking to provide full battery voltage to the coil during cranking. This was done to make up for the loaded down battery which dropped below 12 volts during cranking.
If you have that setup, you would have less than 12 volts to the coil, but it should be around 8 volts I believe.
If that is the case, and that resistor is bad, the truck should still start and run till you let off the starter.
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Joined: Jun 2004
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From: Niceville, FL.
Could be the ignition module is bad (shorted) so that there is a constant current flow through the coil. Take the wire off the "Tach" (-) terminal of the coil and see if the voltage rises to approx. 12 V. with Ign. Sw. in "Run". If so, have the module tested at a parts house. Typical voltage at coil (+) with engine running is about 7.5 to 9 Volts as I remember.
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Just an update! It ended up being the ignition module located on the drivers side fender well. Got a new one, and put it in, and it fired right up. I guess after 28 years the thing went out. I wouldn't have thought about it, untill getting some help from ya'll. Thanks
