912ULS Low Fuel Pressure on Climb-Out

Bob, and John,

Are your carb vent lines and the mechanical fuel pump vent line routed per the maintenance manual? They should not be exposed to any airstream.

John, loose airbox or carb mount fittings should not cause a fuel pressure drop.  You may see other minor issues symptomatic of an engine running lean but fuel flow in this kind of engine has no relationship with intake air leaks.

Jim Isaacs wrote:

Bob, and John,

Are your carb vent lines and the mechanical fuel pump vent line routed per the maintenance manual? They should not be exposed to any airstream.

John, loose airbox or carb mount fittings should not cause a fuel pressure drop.  You may see other minor issues symptomatic of an engine running lean but fuel flow in this kind of engine has no relationship with intake air leaks.

Thanks Jim, all lines are routed correctly. Do you think the colder weather, ambient temps in the 30F range could cause low pressure readings on climb out? Engine runs fine, smooth. Pressure recovers to 3.5-5 psi, has been as low as 1.7psi with the pump on. Stabilizes as I level off. Engine temps always above 150-170F.

John,

To answer your first question, no, if your electric boost pump is operating at the minimum correct pressure when cold. Actually the opposite should occur, the colder a liquid becomes the denser it becomes. Water vapor cooling to liquid then eventually becoming ice as an example, and dense fuel should be easier to push through the lines, again assuming a properly operating pump. What psi output is your electric boost pump?  Have you placed a direct reading* gauge on your electric pump?

Oh, also, are you certain your fuel vent system is unobstructed?

Thanks for the information.  Installed the new higher pressure fuel pump and now the psi at 3.0 and above.  Still, I wonder why all of a sudden we had the problem.

Thanks again.

Bob

Jim Isaacs wrote:

John,

To answer your first question, no, if your electric boost pump is operating at the minimum correct pressure when cold. Actually the opposite should occur, the colder a liquid becomes the denser it becomes. Water vapor cooling to liquid then eventually becoming ice as an example, and dense fuel should be easier to push through the lines, again assuming a properly operating pump. What psi output is your electric boost pump?  Have you placed a direct reading* gauge on your electric pump?

Oh, also, are you certain your fuel vent system is unobstructed?

Fuel vent system is good, have not place a direct reading gauge on it yet. I’m waiting on an oil change as soon as weather cooperates and will check with the gauge. I’ll check the model of the aux fuel pump to ascertain psi next time   I’m at the plane. Thanks Jim.