why wont truck stay running?
have a 1976 f150 4wd with a 390. the truck turns over and fires but wont stay running
unless you keep the key turned. as soon as u let off it dies. have changed the cylenoid,
tested the ignition module and still nothing different.
There is the start circuit and then the run circuit, in the primary. It sounds like the start works and when the key springs back to the run position, your resistor wire circuit is at fault. look at the schematic and the tests in the Ford manual. Those manuals have been widely donated to public libraries for reference. The fuse panel, the switch, the wires, are all suspect because of the vehicles age. A schematic and the tests can help you find where it has been altered, corroded or has a worn ir moisture damaged part perhaps. The duraspark boxes have been consolidated to like 3 different low cost replacement modules. in the event you still have an issue after proving out the run circuit. any circuit that exceeds .5 ohm is considered excessive resistance except a run circuit that is designed to reduce voltage to save the coil after start up.
An ignition feed harness is supposed to be shielded where it traverses the engine longitudinally to reach the ignition parts. alterations to that harness, or an overheating condition can lead to damage and no or "low" spark.
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