On Fri, 12 Nov 2004 03:16:35 GMT, (John_F) wrote:

A spark plug that is broken internally will cause this at high power
settings. Find a spark plug tester that uses air pressure and fires
the plugs under pressure to test the plugs.

I've had bad plugs that have passed that test. I think a problem is that
the pressure in those testers is only a fraction of the pressure that
exists in the cylinder. But it is a place to start.

The problem was rough running. The affected cylinder and plug was
determined by a multi-probe EGT and running on single-mag. The plug passed
the 'test' in the box. But the engine ran properly after that plug was
replaced.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)