Fuel Pressure

03-07-2011, 08:55 AM

gderamel | Fuel Pressure

Can anyone tell me what they get for indicated FUEL PRESSURES on the ground and flying? Something doesn't seem right with mine.

I'm getting 17-19 PSI at 1000 RPM (idle), but the Lycoming Operator's Manual ( if I'm reading it correctly) says I'm supposed to get 20 PSI MINIMUM and 40 PSI MAX. Is Lycoming assuming the pump/engine is inline with the fuel tank - not 5' above like the Seawinds - when they give these figures?

Anyone, please chime-in and let me know what you've got. Perhaps this is normal for the Seawind, but I've got a nagging suspicion that my primary fuel pump is starting to failing (only 300 hours total time??!!).

03-07-2011, 10:17 AM

Jack Ardoyno | Fuel Pressure

Hi Guillaume,

I have been wrestling with engine driven pump fuel pressure for a long time and I do believe that the lift of the fuel has a lot to do with some of our problems.

To wit: Nearly all of the Seawinds I have flown (26 at last count) have a rough idle on the engine driven pump alone. The idle smooths out when an electric pump is turned on. I have tried to rule out other possibilities, such as spark plugs, idle mixture, etc.

One of the tests I do on new Seawinds is to see how high they will climb on engine pump alone. This varies from 4,000 feet to 12,000 feet seeming to depend on the intricacies of the the fuel pressure regulator, which may or may not port into the header tank.

Most of the planes will run at full power with as little as 10 PSI to the fuel servo.

If you have a reliable electric pump (or two) I would not replace the engine driven pump just yet. Always take off and land with an electric pump on, but check fuel pressure with sufficient altitude on the engine pump alone. Reportedly the IO-540 likes to see 35 psi at the servo but will run quite well as low as 10 psi.

I hope this helps.

Jack

03-07-2011, 11:05 AM

gderamel

Thanks Jack. Very helpful, not to mention allaying some anxiety.

Wondering, is there a telltale sign that the ENGINE DRIVEN PUMP is about to go sayonara?

I failed to mention on my initial post that the indicated fuel pressure on the ground (not moving) goes from 25 PSI (+-) with the Boost Pump (Mallory 4060FI) "ON"... DOWN to 20 PSI when I'm climbing out (in flight)?!? Perhaps attributable to plumbing (main tank vent relocated from under wings to leading edge of rudder/engine nacelle)? Once I level off, the fuel pressure usually stabilizes in the 'Green' (>10 PSI?) in the low altitudes but I'm puzzled why it's dipping down to 20 PSI on the takeoff climb with the boost pump on (which was doing 25 PSI on the ground).

03-07-2011, 01:04 PM

Jack Ardoyno | Fuel System

Hi Guillaume,

A frequent culprit in fuel pressure fluctuations and failures has been the fuel pressure regulator. I believe the Mallory is capable of 60 psi. Since the fuel servo likes to see 35 psi, most applications incorporate a pressure regulator in the system. Some of these have openings to both ambient air and a recirculating circuit for excess fuel, sometimes dumping into the header tank. This can be very dangerous if not plumbed correctly. In a number of cases it is suspected that the ambient air has been driven into the header tank pushing its fuel back up into the wing, starving fuel to the engine. I believe you would be well served to inspect and possibly replace your fuel pressure regulator. It may be something as simple as an adjustment up in pressure. Fuel pressure reductions during climbout are common and, I think, are caused by the reduction in ambient pressure coupled with the working of the pressure regulator.

Jack

03-07-2011, 06:27 PM

gderamel

Thanks Jack. I'll check it out tomorrow - report back.

03-07-2011, 07:15 PM

Fred Lohr

If you are looking to replace your regulator, you might consider replacing both pumps and old regulator with the airflow dual pump system mentioned in previous posts. these are continuous duty pumps, so leave them on or turn them off, whatever you like. They are two identical pumps both capable of suppling sufficient pressure in the event of a engine drive pump failure (which i am told are somewhat rare). The orginal seawind "by the book" set up had one mallory pump and one other pump. In my case the mallory pump failed after two or three years and i replaced it. Then, i have always suspected the regulator went bad as well. I would get low fuel pressure warnings. these were not consistent, but occurred when the electical pumps were not on.

all of this was solved by the new airflow setup, and not a single problem since.

you already have the wiring for two pumps back there, so it is just a plumbing job and mounting the new dual pump unit. No need to change anything else. best money i ever spent, simply for the peace of mind

03-08-2011, 07:46 AM

Mike

The dual pump is the way to go. The package simplifies the system. I changed my setup to the dual 2.5 years ago and haven't had any problems. I keep one on whenever the engine is running although in cruise I could turn it off and let the engine pump work by itself. The manufacture of the dual setup does mention it is ok to keep them on all the time. My mallory pump now transfers fuel form one side to the other at about 1GPM. DON'T TRANSFER WHILE FLYING..!!; the engine doesn't like it!!

03-11-2011, 10:10 PM

Ed Lynch | Fuel Pressure

Hi Guillame, I have the "stock" Seawind fuel system as delivered with the kit, and installed according to the book. My pressure while at idle on the ground is 19 psi, and in the air it's 21 to 23 psi on the engine pump alone. Adding the electric pump brings it up to 24 to 26 psi. That's the most I've ever seen. Early on in my flight test hours, I replaced my engine driven pump because I became suspicious of the 19 psi, but the new one gives just the same. By the way, if your regulator has a 1/8 inch hose port on it, it should be tightly capped, not vented, because this was designed to increase fuel pressure on supercharged engines by connecting it to the intake manifold on a car. So leaving it open will lower the regulated pressure as you climb to altitude--not what you want. Lastly, you can increase the regulated pressure by turning in the screw on the end of the regulator, after backing off the locknut. Ed

03-12-2011, 09:35 AM

gderamel

Thanks Ed.

I've opted to switch to another boost pump system made by Airflow Performance Inc. It's a dual-pump package that comes with a new fuel pressure regulator. I don't have the part numbers, but as soon as I do, I’ll post them along with the pricing. Unfortunately the website doesn't include any spec-sheets or more info. Planemakers is ordering it and installing. Shouldn't entail too much work as the wiring is already there - just some plumbing and possibly new mounting brackets. Fred Lohr and Mike Witkowski both have this system installed with no complaints.

Back to your post... which is the "1/8 inch hose port"? (see attached pic). I assumed that was an overflow... but come to think of it I've never seen any fuel stains come out of it. The 'port' stubs out just on the trailing side of the left wing root.

03-17-2011, 08:23 PM

Ed Lynch | Fuel Pressure Regulator

Yes, that small hose nipple should be capped. It is not a vent. Capping it will help your fuel pressure at altitude-- not a problem for me, since I rarely get above 500 feet. Ed