Fuel pressure issues

[DesertNomad]

Recently I have become hyper-aware of my fuel pressure as I feel it might not be behaving the way it used to. I have had my Dakota for 4 years and in the past with the electric fuel pump off, my pressure sat right around 4psi. Turning on the electric pump would push it up to about 6psi. The phase of flight did not seem to affect anything - idle, taxi, cruise, etc.

I have not tracked it well (doing that tomorrow), but at cruise power at 10,000' I saw about 3psi on a recent flight. At about 15" MP and 7,000' it had climbed to about 6psi. Yesterday at Reno I was forced to wait at the hold-short line for about 15 minutes on a 90F day while 5 airliners landed/departed. At idle and electric pump off, with the engine already warm from an earlier flight, it was about 1-2psi and fluctuating a bit. Does that seem too low?

Bumping up the throttle to about 1200 rpm didn't seem to change it. When I was finally cleared for takeoff, at full power with the electric pump on, I saw about 8psi. I have checked the vent lines in both tanks and they are clear. The Dakota maintenance manual says a few things:



I am looking to see if the group here thinks this is normal.

 

[deyoung]

Somewhat late reply here, sorry. Curious what you've seen since?

If the engine never hesitates or stumbles, I'd probably tentatively say watch it and see. Check the fuel filter for obstructions maybe? Possibly the engine-driven pump is on its way to wearing out.

I suspect this is unrelated to your issue, but I do notice for me that when my tanks are completely full, with the electric pump off, my fuel pressure drops quite low while climbing. Not out of the green, and the engine never seems to mind, but near the bottom of the gauge. It comes up with the electric pump on, and it also comes up (without the electric pump) after leveling off. After I've burned off a few gallons it no longer does this.

I've assumed it's a venting issue somewhere, though I could be wrong.

 

[Chip Sylverne]

According to Lyc you only need .5lbs, so you've still got some margin. I know my Comanche pressure drops a bunch under full throttle TO ops when flowage is high, almost to their bottom of the green. Got my attention quick when I first bought it. Checked all the vents, no blockage. Even though it didn't really change much, and the pump wasn'leaking, fuel pumps are cheap so I just replaced it for peace of mind.

Do Dakota's have any known heat-related vapor lock issues?

 

[NordicDave]

From what I understand, The important value is full power operations. What GPH fuel flows are witnessed at full power and corresponding fuel pressure? Carb engines have a low pressure fuel flow. Are the fuel flows matching the values in the POH and are the minimum/max pressures within the range specific in your engine manufacturer's operations/maintenance manual?

My O-470R pressure range is .5 to 6 psi depending on applied power. Reno is high & hot thus Mother Nature restricts max power and corresponding required fuel pressure required to maintain GPH per manifold pressure.

-David

 

[unsafervguy]

The pump may be getting a bit weak, but at those temps and idling for that long there may have been a bit of boil off going on at idle. I would watch it for a while and see what it does.