[Shehryar Hassan]

Hello

Recently I encountered a problem with MFI-17 aircraft (Lycoming IO360A1B6 engine) where the fuel flow rise 2 GPH whenever boost pump was turned OFF. (electric boost pump is in parallel with ED pump)

There seemed to be no problem with fuel nozzles, divider, injector, ignition system or air system. The boost pump have been checked on test bench and is operating in its normal pressure limits.

I have a doubt on faulty ED pump but can't workout a logical reason for this odd problem.

Any suggestion would be appriciated.
Regards
Shehryar

[Paul_Sengupta]

A1B6 engine!

What fuel flow gauge is this? Is this the one which operates on fuel pressure from the spider at the top of the engine, where the gauge is sometimes marked in "fuel flow", or is this an actual fuel flow gauge somewhere in the lines?

I'm not going to know the answer to your problem, but narrowing it down might helps someone diagnose it!

[carlmeek]

My aircraft fuel flow reads a completely different number if pump is on or off. Probably caused by turbulence or pressure or something. However the actual amount of fuel going into the engine is unchanged.

[Shehryar Hassan]

A1B6 engine!

What fuel flow gauge is this? Is this the one which operates on fuel pressure from the spider at the top of the engine, where the gauge is sometimes marked in "fuel flow", or is this an actual fuel flow gauge somewhere in the lines?

I'm not going to know the answer to your problem, but narrowing it down might helps someone diagnose it!

Yes, this fuel flow gauge is the one whose input line is taken from fuel flow divider. So it is basically pressure calibrated for fuel flow I guess.

[Shehryar Hassan]

It is basically pressure taken from fuel flow divider. It means fuel flow gauge is calibrated for pressure may be.

[Dusty_B]

Can’t tell you why, but I can tell you that it is not unusual! Seen it on a few aircraft.

[Ian Melville]

Don't know scecifics for that aircraft or engine, but....
If the fuel flow is derived from pressure then yes I would expect to see an increase if the electric pump is turned off. If fuel by the engine is increased (opened throttle) for a fixed pump output, the the pressure in the pipe work downstream of the pump/s will drop. Likewise if the flow to the engine remains constant and you reduce the pumped output ( turn off a pump) the pressure will also drop giving the impression that fuel flow has increased.