Fuel Pressure

[grainfarmer]

IO-320 fixed pitch over the last couple x countries, at higher altitudes, Ive noticed that my fuel pressure is at the bottom side of the green arc if not out of the green. Not low while scud running and scouting. Boost pump brings it up a little. Any thoughts?

P.S. Gotta throw this in, BFR last week, the CFI couldn't get the grin off her face after she took the controls and personally thanked me for using my plane. Tally another grin!!

[Ron Lee]

If carbureted I see that all the time. In over 1600 hours no miss due to low pressure.

[664781]

It's a RV thing.....Feaks out new pilots who see it for the first time.LOL

[rjcthree]

The question was about the indication of low fuel pressure specifically at high altitudes. Does this mean fuel pressure is solidly in the green at lower altitudes? If so, there are a number of things to check. If it's always low, there are other things to confirm.

As I understand the design of the VDO pressure sensor (fuel or oil) it references atmospheric pressure; high altitudes would indicate HIGHER sensed (reported) pressure, all other things being equal, they aren't. I cannot speak to the accuracy of the temperature compensation that may or may not modify the signal, for instance.

Regardless, if you are concerned about low indicated fuel pressure, first thing to check is if the pressure is really low - your choice, you can check the fuel pressure with a known accurate secondary guage or check the indicator against a known pressure, find out what it reads. From there it gets easier.

This just rings of 'early indicator'. But I'll admit to being suspicious.

Rick 90432

[Ron Lee]

My field elevation is 6840 feet. Seldom do I cruise below 10,000' MSL.

[Sam Buchanan]

Originally Posted by grainfarmer

IO-320 fixed pitch over the last couple x countries, at higher altitudes, Ive noticed that my fuel pressure is at the bottom side of the green arc if not out of the green. Not low while scud running and scouting. Boost pump brings it up a little. Any thoughts?

P.S. Gotta throw this in, BFR last week, the CFI couldn't get the grin off her face after she took the controls and personally thanked me for using my plane. Tally another grin!!

Originally Posted by Ron Lee

If carbureted I see that all the time. In over 1600 hours no miss due to low pressure.

Originally Posted by 664781

It's a RV thing.....Feaks out new pilots who see it for the first time.LOL

I believe the IO-320 is fuel injected so I would be hesitant to explain this one away with the well-known sensor issues on carbed engines. If the problem is indeed altitude sensitive, it might still be a sensor problem. But if the pressure fluctuates at various altitudes, me thinks the sensor and/or pressure needs to be checked. Could be a pump getting weak.

[Ron Lee]

Good catch Sam. I missed the IO part so disregard my comments reference my carbureted setup.

[grainfarmer]

My bad, its carbureted Updated my logbook just last week actually and have 68 fun filled, smiling hours in my RV. 60 of which have been 3000' msl and the other 8 at 8500-9500 msl. At 3000', its at the top of the green arc. Thanks for the replies.