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Continuous spark with motor not running 700 1988

posted by  Flemming on  Sun Dec 31 07:01 CST 2006
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last visit: Tue Aug 13 09:22 CST 2013
[RELATED]

After doing some major PM on my 1988 780 B280F -- new coolant hoses, injector seals, knock sensors, and TB cleaning -- it won't start. Initially it would run for about 5 seconds and die. If I touched the accelerator it would immediately die. While trying to diagnose the problem I was surprised to have the motor turn over on its own when turning on the ignition (position 2). I traced this down to the coil producing spark when the key is turned on (position 2) -- it's a continuous spark! Assuming it's a false signal to the Ignition CU, I started unplugging sensors, including the Injection CU. It made no difference, the only way to stop this behaviour is to unplug the Power Stage or the Ignition CU. Though this sounds like a failing Ignition CU, I'm more inclined to think it's a wiring problem as I moved it about quite a bit while pulling the intake manifold. Any suggestions or thoughts as to what the problem is with the coil producing a spark without the motor running would be welcome.






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