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-   -   Fuel Pump Issue (https://vansairforce.net/community/showthread.php?t=105609)

BillL 10-21-2013 07:50 PM

Bob,

First, congrats on flight testing. 2nd, could you share some of the pressure vs time data?

Just because the high pressure electric pump can provide the fuel, (you have 2 sources of data, 58 GPH, and consistent 26 psi) does not mean there is not a suction leak or high restriction resulting in cavitation somewhere between the mechanical pump and the tank. It seems too obvious just to blame the mech pump. Where do you have filters and screens? I think those would be the fist place to start diagnostics. A new system is the most contaminated it will ever be.

Back to data, you said the pressure decreased not dropped when switching the electric pump off. It takes a little time to build up vapor in the line if either a suction leak or just high suction and vaporization.

Just wondering - -did you do any kind of fuel system, from tank to firewall pressure test to check for leaks? I was thinking about an air pressure test with a leak down type of test for small leaks. Maybe suction?

rleffler 10-21-2013 07:51 PM

I'm going to make a call to Lycoming again in the morning to debate the warranty status.

I've found that Tempest has a equivalent model for about $100 less. Does anyone have any experience with them or can comment on their quality?

Thanks,

Bob

Bill.Peyton 10-21-2013 08:03 PM

Bob,
I know the quick solution is to replace the pump, but I too am thinking you have a restriction or leak in the system between the mechanical pump and the fuel selector. I know you replaced the aluminum lines with flex line. I would pull all the lines and verify that there are no restrictions or flaps inside the hose. Prior to that I would pressurize the entire system from the fuel pump inlet line to the tank, and do a leak down test. Just thinking out load......

CharlieWaffles 10-21-2013 08:14 PM

Bob, any chance you have the Andair fuel pump or did you go with the stock one?

rleffler 10-21-2013 08:26 PM

Quote:

Originally Posted by CharlieWaffles (Post 818620)
Bob, any chance you have the Andair fuel pump or did you go with the stock one?

No, the standard AFP boost pump.

Bob

douglassmt 10-22-2013 09:25 AM

Level flight?
 
My fuel pressures drop in climb with just the mechanical pump (same during my transition training in the company -10), so I leave the boost pump on through most of the climb. You didn't really say, and I assume the pressure drop was in level flight, but if it was in a climb, it's pretty normal.

ScottSchmidt 10-22-2013 10:29 AM

Quote:

Originally Posted by douglassmt (Post 818742)
My fuel pressures drop in climb with just the mechanical pump (same during my transition training in the company -10), so I leave the boost pump on through most of the climb. You didn't really say, and I assume the pressure drop was in level flight, but if it was in a climb, it's pretty normal.

Yae, same thoughts from me.

Were your fuel tanks full as well? When I fill my tanks to the top and climb out for an extended period of time I will get a fuel pressure drop that will trigger an alarm. The second I level off and burn off some fuel it goes away. My hypothesis is that the fuel breather gets fuel in it and then the mechanical pump has to pump the the fuel from the tanks with a "plugged" breather hose that is filled with fuel. It won't do it if the tanks are not full.

douglassmt 10-22-2013 10:38 AM

Hmm
 
Quote:

Originally Posted by ScottSchmidt (Post 818775)
Yae, same thoughts from me.

Were your fuel tanks full as well? When I fill my tanks to the top and climb out for an extended period of time I will get a fuel pressure drop that will trigger an alarm. The second I level off and burn off some fuel it goes away. My hypothesis is that the fuel breather gets fuel in it and then the mechanical pump has to pump the the fuel from the tanks with a "plugged" breather hose that is filled with fuel. It won't do it if the tanks are not full.

Hmm, I hadn't made that correlation. I just assumed that the nose up attitude created a greater head between the fuel pickup line and the engine, so a boost is necessary. I'll check it next time with full and not full tanks.

Wayne Gillispie 10-22-2013 11:18 AM

Ours runs 28-29 psi in cruise and 19-20 psi during full fuel climb without boost pump. If it went below 15 psi or ran rough/lean then I would turn it on.

rleffler 10-22-2013 11:33 AM

Quote:

Originally Posted by ScottSchmidt (Post 818775)
Yae, same thoughts from me.

Were your fuel tanks full as well? When I fill my tanks to the top and climb out for an extended period of time I will get a fuel pressure drop that will trigger an alarm. The second I level off and burn off some fuel it goes away. My hypothesis is that the fuel breather gets fuel in it and then the mechanical pump has to pump the the fuel from the tanks with a "plugged" breather hose that is filled with fuel. It won't do it if the tanks are not full.

No, the tanks were about 2/3 full and this happened in both climb and level flight.


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