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low fuel pressure

F

Florida John

I'm New Here
Hi all my first post. I bought my RV12 completed, builder deceased, and have been battling fuel pressure for ever 54 hrs on it.
Flying yesterday I had 1 psi at 5400 rpm oat 53 deg. both pumps on . shut off elect pump 0.7 psi.
First I replaced the Facet #40105 pump 3 to 4.5 psi with Facet pump #40106 4 to 7 psi on the ground wit h a mech.gauge installed 2 psi ,mech. gauge and skyview read the same, next I replaced the Pierburg pump with a new BCD #893110 pump and. , cleaned gascolator screen. still low .
when climbing sometimes I can feel the engine stumble .The plane is a EAB
Thanks John
 
Remove the gascolator drain and with the electric fuel pump running, Time from the fuel valve opening until 1 gallon has emptied into a container. Max Time should be less than 180 seconds, typically about 2 minutes.
An orifice is in the fuel return line. If it is missing, that will cause low fuel pressure.
Assuming the fuel pumps and pressure gauge are working OK, then low fuel pressure can be caused by an obstruction in the supply line, a leak, or excessive fuel flow in the return line.
 
Welcome - Florida John

Welcome to the VAF, John. And please let us know about your progress in trouble shooting this problem. That's how we all learn. Best to you!
 
John, welcome to VAF. Sounds like you are doing the correct things to trouble shoot. The best piece of information you put out was that you already confirmed the accuracy of the pressure sensor and Skyview by using a mechanical gauge. Combined with the engine "stumble" I would say you have proven that this is a "real" problem rather than an indicator problem. Also confirming this is the fact that both or either fuel pump produces low pressure, and it is highly unlikely that you have a dual failure. This leads me to the conclusion that you are most likely missing the orifice in the fuel return system, and there is therefore a high volume of low pressure fuel being returned to the tank. You didn't say who the builder was, and obviously you can't ask him or her questions about this, so I suggest taking the fuel hoses apart and checking against the original plans. Hopefully you got the plans with the plane, but if not you can get them from Vans website or from one of us. Keep us in the loop, I'm sure by now there are a bunch of us with our curiosity aroused!
 
Read plans page 46-11:
RV-12 Engine install plans
It says, "WARNING: It is possible to install the VA-216 Fuel Return Assy.
with the ends reversed which WILL RESULT IN LOW FUEL PRESSURE.
Double check to verify a proper installation."
 
If you have a bore scope you can see the fuel return line looking down the tank filler port. If properly installed you will see it just barely overflowing when the electric pump is running with the engine off. If it's squirting (judgment call here) the orifice is not restricting return flow which means it was never installed or the assembly is wrong.

I had a hi flow alarm once which caused me to observe the return line flow and verify the orifice in place. I doubt your engine would run above idle if the orifice was in the line to a carburetor, but I can't say that with certainty.
 
When troubleshooting, never look in the fuel filler hole while someone turns on the fuel pump.
If the previously mentioned fuel hose is installed backwards, the return line will shoot fuel all the way up to the fuel cap.
 
Thanks for that information Scott. It might prevent someone from getting splashed in the face with gasoline. Observing the the fuel return in the tank can also help "Florida John" troubleshoot his low fuel pressure problem without taking apart fuel lines.
 
Scott, I've never seen one without the orifice, so I defer to you. The method is still valid. Remove the cap, start the pump and if you don't see a squirt use the bore scope to check it out. If you do get a squirt the evidence is conclusive.

Rich
 
Thanks all for your help. took the fuel line off at the mech pump 123 sec. to pump 1 gal of fuel.Looked in the fuel fill neck slow steady flow, not squirting.The restrictor is in the banjo bolt .Now waiting for a new fuel pressure gauge that I can install permanently.Will let you know results.
john
 
Mike,

It's been a while since I messed with this, but as I recall the restrictor orifice for the return line is not the pilot jet. The restricting orifice is not accessible without physically removing the return line from the manifold block. That's why the blow test is used to verify the configuration.

Rich
 
RV12

Thanks to all for your help All fixed mrt 980 was right I removed the jet from the banjo bolt and the pressure came up to 5 psi with one pump on
again thanks to all john
 
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