Low fuel PSIs at high power

Hello!

So I recently finished the install of the Dynon D-10 EMS which is great except for the fact that now that I have a working fuel psi gauge I have noticed significant drops in fuel PSI on high power events like takeoff or climbs without using the boost pump. It'll drop down to 1 PSI with the throttle wide open. When I use the boost pump it'll put the pressure back up and hold it around 4-5 after that. It'll maintain good pressure at cruise.

I'm just wondering if this is normal. Looking at the O-360 1A1 section it states 8 MAX, 3 nominal, .5 minimum. My question is, does this seem normal or is it indicative of a failing engine driven pump? I haven't noticed any significant loss of power during this drop.

Thanks all!

CW

I have seen a problem similar to this when there was a partial kink in a line, easily letting a certain amount of fluid through, but at high-demand times, it could barely keep up. Have you checked all of your fuel lines?

First, I would encourage you to always use the boost pump for takeoffs. It would be a really bad time for a fuel pump to fail in a low wing airplane.

Leaks in the hoses will allow air in, so check all of them for proper tightening and no leaks. And check the gascolator screen as well.

Vic

I definitely have started using my boost pump for all takeoffs now. So to confirm, this is not normal even though Lycoming states .5 PSI is min and lowest I've seen is 1psi (though I think the dynon's only working in whole increments). I'm going to do some more troubleshooting and see if I can isolate it to a specific side.

There's a small dent in the left tank's supply line where under the wing fairing right before it runs into the fuselage. I didn't think it was large enough to cause any significant restriction but perhaps it is. Next time I take it up I'll see if it's just when running on the left tank. Otherwise I'll check the gascolator screen.

Doesn't sound like failing pump?

WingnutWick said:

I definitely have started using my boost pump for all takeoffs now. So to confirm, this is not normal even though Lycoming states .5 PSI is min and lowest I've seen is 1psi (though I think the dynon's only working in whole increments). I'm going to do some more troubleshooting, and see if I can isolate it to a specific side.

There's a small dent in the last tank's supply line where under the wing fairing right before it runs into the fuselage. I didn't think it was large enough to cause any significant restriction but perhaps it is. Next time I take it up I'll see if it's just when running on the left tank. Otherwise I'll check the gascolator screen.

Doesn't sound like failing pump?

Click to expand...

.5 PSI is the minimum safe pressure but that does not mean it is normal (for an RV it is not).

It is normal for some RV's to have a reduction in pressure during a long climb. This is usually in hot temps.

It is standard operating procedure to always use the boost pump during tack-off and landing.

It could be a failing pump, but it could be a lot of other things also. Dynon has a document on their web site related to fuel pressure sender accuracy with changes in ambient pressure (such as climbing). I don't think recently delivered sensors would be effected by this but it is worth checking.

I had exactly the same problem with my o360 RV7. Tried a new pump, insulated fuel lines, cooling shroud and blast tube on pump, etc... no help. I saw another RV where the builder had added short extensions to the tank vents on the belly. I took a couple pieces of soft aluminum tubing and made extensions with the open end facing forward in the slipstream, sort of a ram effect to the vent. Problem solved!! I now see a steady 5-6 psi all the time. Quick and easy! Hope this helps.
Jim

Charles, I would encourage you to test the fuel pressure with a KNOWN mechanical gauge to verify if you really have a pressure issue, or an instrumental issue. We see it all the time where guys will spend months chasing a pressure issue, spend lots of time and $$$$$ replacing pumps, hoses, rigid tubing, rebuilding tank vents, etc, and an intermittent connection at the pressure sender was the big issue.

NOT to say there maybe a real failure here, but test---dont guess.

Tom