Unexplained EGT surge in level cruise

[varlajo]

Timeline of events as follows:

* I must say I did not catch the out-of-nowhere increase in all CHTs until I analyzed EIS data after the flight (although CHT3 only momentarily increased above 380F).

* What I did notice was a drop in oil pressure from the usual 66-67 PSI to 64 PSI, whereupon I increased engine RPM from 2400 to 2450

* This immediately brought oil pressure back where I wanted it

* I then re-leaned the mixture to 50 LOP (see peak in FF)

The observed drop in oil pressure seems to coincide with an abrupt and rapid increase in all four EGTs and then CHTs and subsequent slight flutter in fuel flow and fuel pressure. The commanded increase in engine RPM immediately brought all EGTs and CHTs down to normal (why??), and they stayed there after re-lean. 

I am curious about the reason behind the EGT spike. This occurred at level cruise at 6500 ft at 61% power (2400 PRM, WOT, 7.9 GPH), approx. 45 minutes at this setting. Shown are EGT vs FF and CHT vs oil pressure (red line is 385F). The vertical line is both charts shows the time where EGTs started to increase. 

The complete timeline of the charts is approx. 30 minutes. 

Edited May 12 by varlajo

[DXB]

Seems most likely just a transiently fouled plug on #1.

Or maybe a partially clogged injector? 

[varlajo]

5 minutes ago, DXB said:

Seems most likely just a transiently fouled plug on #1.

Or maybe a partially clogged injector? 

Oh, the momentary spike in EGT1 at 01:18 does not worry me much. The 50 degree increase in all EGTs and subsequently all CHTs starting at 01:05 does. 

[N201MKTurbo]

If all your EGTs went up, a mag probably quit working. If it does it again, do a mag check.

[varlajo]

3 minutes ago, N201MKTurbo said:

If all your EGTs went up, a mag probably quit working. If it does it again, do a mag check.

Yep, this was my first thought as well. Just found it curious that a minor adjustment to RPM and FF immediately fixed it. 

[N201MKTurbo]

1 minute ago, varlajo said:

Yep, this was my first thought as well. Just found it curious that a minor adjustment to RPM and FF immediately fixed it. 

Your adjustments may just be a coincidence. It may have came back on line if you did nothing. I have had mags do this where it just goes offline for a few seconds and comes back. It is usually because the point gap has gone to nothing. This may be caused by a bad condenser. 

[varlajo]

1 minute ago, N201MKTurbo said:

Your adjustments may just be a coincidence. It may have came back on line if you did nothing. I have had mags do this where it just goes offline for a few seconds and comes back. It is usually because the point gap has gone to nothing. This may be caused by a bad condenser. 

Good point. Do you observe engine RPM drop when your mag goes offline for a short time?

[N201MKTurbo]

I never noticed and I didn’t have a recording monitor. The power will drop a little and it may take a bit for the prop to catch up. Just like when you do a mag test and the RPMs drop a bit on one mag. The same thing will happen in cruise.

[varlajo]

4 minutes ago, N201MKTurbo said:

I never noticed and I didn’t have a recording monitor. The power will drop a little and it may take a bit for the prop to catch up. Just like when you do a mag test and the RPMs drop a bit on one mag. The same thing will happen in cruise.

My RPM remained rock solid at 2400 throughout the 10-minute event.