Low Fuel Pressure o-320 160 HP

[vlittle]

OK, here's a puzzler that I worked out. Let's see if any of you folks can determine the problem/solution.

On the first flight after my annual, my low fuel pressure alarm sounded, with fuel pressure showing 1 psi, even with the boost pump on. In flight debugging showed that I could get it to 2 psi by flying slowly (low engine power) with the boost pump on.

I also experimented with positive and negative G's with no affect.

I did notice a fuel flow increase when the boost pump was on, which is normal and indicated that the pump was working. The engine ran normally throughout.

Post landing engine-off checks indicated that the boost pump was working, but could only generate about 4psi, where 6psi is normal. So what's your guess of the problem and how to fix it (hint: no replacement of parts was necessary to fix this. Fix took about 15 minutes)?

V

 

[LifeofReiley]

Forgot to remove the protective sleeve over the fuel vent?

Or, bleed air from gascolator after servicing?

 

[gasman]

Bad electric connection on your sender.

 

[Doug]

Cleaned the air bleed hole on the end of the transducer?

 

[jwall]

have RV6A and experienced low pressure. boost pump on, pressure was eratic, then dropped to .5 lbs. after landing, checked pump, pressure came up O.K. engine ran O.K. during flight. hope you can get some insight to this problem Vern? Thanks. John

 

[vlittle]

Cleaned the air bleed hole on the end of the transducer?

Everyone's on the right track. So here's the fix:

As I mentioned, this was the first flight after the annual. I had removed the fuel line from the carb to clean the inlet screen, plus drained and cleaned the gascolator.

I thought that there might be air trapped in the system, so I backed off a pipe plug on the Van's sender manifold to bleed the air from the fuel pressure sender. Turning on the boost pump ensured that the air was out (indicated by fuel leaking from the pipe plug). Turn off boost pump, tighten the plug and fuel pressure was up to 6 psi indicated.

I was wondering why this has not happened before (last 6 years), and I think I know why. When I released the fuel line from the carb, it dropped down and spilled it's load on the floor. In previous years, I remember bending the line up to keep the fuel in it. So I think the fuel drained out of the pressure sender line, entrapping the air. That's my theory, so I'm sticking too it!

V