Sudden EGT spike on all 4 cylinders

[Jake14]

Thanks,
The questionable FF indication seems to be a dropped (1-sec sampling rate) data point on the AFS5500 EFIS. It shows up on other data as well. See here:

SavvyAviation

apps.savvyaviation.com

However, I do have a new red cube on order since it's the only item between the fuel pressure monitoring point and the servo and the one I have is a few years old. I guess it could be restricting flow while pressure still reads high. Also, the chart which plots the EGT's vs G-load shows the fuel flow dropping right at the time I pull up from around zero G at 18:20, see below.
Since there's a turbine wheel spinning in the red cube, I suppose it may have been affected by the gyro or g forces?


I agree with you that the data indicate an un-commanded reduction in fuel flow, so my plan is to replace the entire fuel system from the boost pump to the injector nozzles with the exception of the engine driven fuel pump. The components are coming up to 10years and 1,000hrs so I don't feel too bad about doing it. The fuel hoses are 10 years old too so I'm going to replace those as well on the outside chance that they may be causing some kind of restriction.

The other point is that the in-flight incident was different after the EGT spike since I was able to fly back to the airport. If it had behaved like it did on the static runup, I wouldn't have made it back. Maybe the problem in flight was somehow exacerbated on the ground runup.

Thanks for all your comments and insights.

 

[lr172]

Thanks,
The questionable FF indication seems to be a dropped (1-sec sampling rate) data point on the AFS5500 EFIS. It shows up on other data as well. See here:

SavvyAviation

apps.savvyaviation.com

However, I do have a new red cube on order since it's the only item between the fuel pressure monitoring point and the servo and the one I have is a few years old. I guess it could be restricting flow while pressure still reads high. Also, the chart which plots the EGT's vs G-load shows the fuel flow dropping right at the time I pull up from around zero G at 18:20, see below.
Since there's a turbine wheel spinning in the red cube, I suppose it may have been affected by the gyro or g forces?

View attachment 111635
I agree with you that the data indicate an un-commanded reduction in fuel flow, so my plan is to replace the entire fuel system from the boost pump to the injector nozzles with the exception of the engine driven fuel pump. The components are coming up to 10years and 1,000hrs so I don't feel too bad about doing it. The fuel hoses are 10 years old too so I'm going to replace those as well on the outside chance that they may be causing some kind of restriction.

The other point is that the in-flight incident was different after the EGT spike since I was able to fly back to the airport. If it had behaved like it did on the static runup, I wouldn't have made it back. Maybe the problem in flight was somehow exacerbated on the ground runup.

blockage can be like that. sometimes it blocks nothing and sometimes a little and sometimes a lot. G forces could have dislodged the debris, then plugged something partially. with debris floating around in the system, all sorts of strange things can happen.

 

[lr172]

w, so my plan is to replace the entire fuel system from the boost pump to the injector nozzles with the exception of the engine driven fuel pump.

no gaurantee there is no debris in the fuel pump. may not be the source, but it could have ended up in there.

 

[Jake14]

I'll flush the system when it's opened up

 

[jcarne]

Any updates on this sir?

 

[Jake14]

Just to close out this thread:
Spent several weeks getting the servo ordered and replaced. The first servo fell out of the car door when I opened it and leaked when I installed it. Apparently there's a very tight tolerance press fit connection which can be damaged even in a drop of about a foot. The next servo was set way too rich and gave 250+ rpm mag drops and FF was 7.8gph at mag check vs 4.6 on the old servo. Sent it back and the third time lucky servo is now working fine. Anyway, wound up replacing the fuel system from engine fuel pump forward, All hoses, red cube, servo, spider, injectors. Engine runs great now and all temps and fuel flows are as before the incident. Never found the cause but suspect the servo.