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FCU Investigation

The engine ran quite happily up to the start of 2012 and then refused to start!

An investigation soon showed that there was no HP fuel coming out of the FCU. A bit more fiddling and there seemed to be no HP fuel inside the FCU on the HP gallery either (there is an access port).

I decided to have a peak inside the FCU and see if anything was obviously wrong. It is a seriously complicated thing and unfortunatly most of the interesting parts have lee-style seals protecting them, but you can still access some of the major components without drilling things out.

 

Fuel Control Unit

Fuel Control Unit

 

Fuel System Schematic

Fuel System Schematic

 

 

First stop was to have a look at the fuel inlet filter. We did see lots of LP fuel coming out of the inspection port so it wasn't likely to be blocked though.

 

 

Fuel inlet and filter

Fuel inlet and filter

 

Fuel Inlet Filter

Fuel Inlet Filter

 

 

The next critical part is the pressure regulator. It's quite simple and just consists of a spring loaded bypass valve.

 

 

Fuel pressure regulator

Fuel pressure regulator

 

 

This bit is the internal filter that feeds the throttling pack.

 

 

Throttling pack filter

Throttling pack filter

 

 

And this is the HP outlet to the fuel injector. There is a minimum pressure valve in there but that lee-style seal stops it being removed for inspection.
As I wasn't seeing any HP fuel from the inspection port it can't be the problem, luckily.

 

 

HP outlet and minimum pressure valve

HP outlet and minimum pressure valve

 

 

So everything looks pristine and undamaged. The next possibility is that there is a fault in one of the accessories that is commanding no fuel. A possible culprit is the overspeed limiter/automatic shutdown device.


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