Robert,

I would eliminate a spark plug problem before thinking about anything else.  If one plug is not firing, the EGT will rise somewhere between 100 and 200 degrees.  But why would the plug stop firing during a low manifold pressure lean condition?  A lean mixture is harder to fire than a rich one and maybe this plug is marginal.  Do a mag check when the condition exists and I'll bet you'll find that on one of the mags the EGT will show which cylinder is not firing.  That will pinpoint the plug not firing.

Just my guess.

Gary Casey

 

Last week I had been cruising LoP and during the power back for landing
Cyl #3 suddenly jumped 125F and sent the Chelton lady shouting into my
ear. That would not be unusual if I had failed to either further lean
or go full rich but in this case I had leaned and the other 5 cylinders
were OK. I leaned way back and really lost power and then went full
rich, and it finally settled down. On the return flight I reduced power
and carefully kept leaning and had no problem. Yesterday it was deja'
vu all over again. Powered back on approach and only #3 went nutso
until I leaned even more. On the return flight there was no recurrence.


Does this sound like a problem with the injector, with the thermocouple,
or ? ? ?

Robert Simon