At 04:49 PM 5/13/2016, Scott wrote: >while there, look for an insulated spark-plug wire pulling pliers ... >so you can pull off one plug wire at a time while it's idling. The problem with doing that is it violates the Bentley instruction that it's ok to ground the high voltage, but never let it run open circuit (because the resulting high voltage puts too much stress on insulating components in the system, possibly including the internal structures in the driver transistor**). And damage of that sort to a transistor can be cumulative, so it shows up as a failure down the road and not immediately. This is a hallowed old technique but it's not safe with modern ignition systems. **Using a scope I've measured roughly 450 volts for a few microseconds per firing pulse on the coil negative terminal -- that's why the tach bites you if you touch the connection. If the high voltage were not allowed to arc to ground I'd expect the primary voltage to go much higher, which would directly stress the extremely thin insulating layer inside the driver FET (field-effect transistor). Yrs, d |
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