Tom,

 

One of the ways the EGT temps can abnormally increase is if fuel is being burned in the exhaust because it was not completely burned in the cylinder. In such a case the CHTs might be lower than expected for the throttle position.   Just something to consider.  Remember in injected engines that fuel is delivered constantly in the intake area - not much of a problem at high rpm.  But it can be a problem at very low rpm (too much fuel awaiting to be sucked in when the valve opens,  except that MAP also affects the flow (lo MAP, lo flow).  The pressures appear to be in range but the flow change was interesting - maybe a problem with the throttle body or flow divider or, maybe a hiccup (technical term) in the ignition with a late spark.   ???

 

Scott Krueger  

 

Folks

Yesterday I had quite a start on short final on the ILS into Dulles. My MFD started to complain wildly about high EGTs. My high limit is set to 1525 which I never see in normal operations

All cylinders on my io360 were starting to exceed my red line and climbing rapidly.  I had my Dukes boost pump on, my facet belly pump on and pressure was 28psi.  I switched tanks; no change.  Naturally I was thinking about what to do if the fan quits a half mile off the end.  Since I am writing this, it did not quit!  This is the first time I have seen anything like this in 200hrs on the airplane.

By the time I got to the FBO, almost 1.5 mile taxi, I ran the engine up every which way, mag switch, low power high power etc and could not replicate the problem.  One thing I did notice however was that when I turned ON the Facet at low power (13-15 inches MAP) and with the boost pump on, the line pressure increased from 22psi to 28psi (no surprise there) but the indicated flow rate went from about 5 gal/hr to less than 2 with some noticeable increase in EGT.  That surprised me and I never noticed it before, mainly because I never have only one of the pumps turned on at a time at takeoff and landing

I pulled the cowl and checked all was normal, no leaks etc. everything tight no ice in the inlet and so on and then buttoned it up and went about my business. 

Fast forward two hours, filed to get out of IAD, thorough engine runup, flipped the Facet pump on and off, same behavior as before.  High power runup with all pumps, good fuel flow, pressure and    EGTs. Long taxi to runway, decided on another mag check, all good, so good to go.  Cleared for takeoff, takeoff run fuel flow good 19gph, temps good, rotate, on my way.

Approach to home airport 1hr later, did not run backup pump, uneventful approach, temps normal


So after all this, i am none the wiser on what happened on my approach to IAD.  The only thing that was different from what I might have done in the past is that ATC asked me to hustle since I had a heavy in trail.  I was sliding down the ils banister at 140kias until 3 miles out and it was shortly after that that things went pear shaped.  So I am thinking I had the throttle nearer to idle than usual and the engine was likely being driven by the prop.  So is it a fuel servo problem where it is not regulating flow correctly at the very low end with the front door almost shut.  I would have expected rich rather than the other way round but 4 high EGTs can't be wrong.  My servo is the standard Precision Airmotive RSA 5ad1 serviced 30hours ago by an authorized shop. 

Sooo.. Anybody have a similar experience with their engine or thought on what might have caused the anomaly?

I am pulling the flight data out of the mfd tonight to see if there is anything obvious there

Thanks

Tom
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