Engine driven fuel pump acting up...??

[hughfi]

Hi there,

I am experiencing some unusual problems with my engine driven fuel pump on my O-320 E3D

Basically, it indicates correctly when down below 6000ft or so, but when I continue climbing up above that, the pressure drops to 0, or at least between 2lbs and 0lbs. The engine never actually splutters so I doubt the pump has actually stopped working and when I start down again, the pressure from the engine driven pump starts to rise back to normal again.

When I bring on my boost pump while showing 0lbs on the gauge, the pressure does rise back to the bottom of the green again, which tells me the gauge is working o.k.

[What I have tried so far]

1.) Checked all pressure lines to verify there are no leaks at the fittings going into the pump as well as those going into the pressure block. All seem to be fine.

[What I am thinking]

1.) The pump does not have a cooling shroud around it, so is heat hurting the pump substantially? Is this a sign that the pump is wearing out? The fact that the pressure readings are correct when I start down (and have significantly more cooling) leads me to believe that his might be the case.

[Questions]
Is my pump just wearing out and needs to be replaced?
Do I need a cooling shroud on this pump to be safe?

Any help anyone can provide would be greatly appreciated.

Thanks,

Hugh.

[MontanaMike]

Hugh...I don't have a direct answer to your question, but yesterday I spent about 2 hours reading about fuel pressure and guage problems, similar to yours, after searching "fuel pressure" to help me design my FP gauge installation.

The threads were very interesting and will likely be very helpful to you.

Good luck.


MontanaMike
RV-6 N918MB Reserved

[Kyle Boatright]

If your pressure shows as too high (or higher than expected) during descent, you're seeing the same problem that lots of us have scratched our heads over in the past.

Common wisdom is that the fuel pressure sending unit (probably automotive) has too small of a vent hole (its static reference), and reads low on climb out and high on descent.

[Ron Lee]

Mine has read low for about 1100 hours...maybe longer. Engine has never stopped. I biased my Rocky Mtn engine monitor to add 1 psi so it does not blink at me. Of course you want to verify that there is no real flight impacting issue.

[Wallbangar]

HAD ONE THAT THE BOLTS ON THE BOTTOM WERE LOOSE AND LEAKING ON THE HANGAR FLOOR. ALL 340 HOURS SINCE NEW HAD LOW FUEL PRESSURE READINGS (1-3PSI) WITH SLIGHT INCREASE WITH BOOST PUMP ON. SINCE INSTALLATION OF NEW PUMP, PRESSURE INDICATES 4-5PSI WITH BOOST PUMP OFF. INFO ONLY.

[grantcarruthers]

Mine has been similar on the -4 I bought and I plan on looking at it in April with condition inspection.

My Thoughts???

Is the pressure gauge placed where it doesn't 'see' the mech pump pressure? IE, is the gauge in line before the mech pump? I have no idea. If my fuel pressure is at the carb itself and should register from either/both the mech and electric fuel pumps, my mech pump or gauge must be broken as the gauge frequently reads zero. Engine couldn't care less, runs fine with zero registered on the fuel pressure gauge, makes pilot nervous though.

As far as fuel pressure in climb vs decent, I think in mine it seems to have to do with attitude and relative fuel tank position. In the climb, nose up, the tank is relatively lower than the carb, thus less gravity fuel pressure. In the decent, nose/carb lower than the tank, higher gravity fuel pressure?

Clear as mud??