Initial fuel flow tests - no fuel

Flying Canuck · #1 03-30-2018, 01:28 PM

I'm scratching my head today. Just tried to do my fuel flow test on my nearly ready 9A. I have a FlyEFII boost pump with pre-filter coming out of my fuel selector. Goes to a firewall mounted Andair gascolator (Canadian requirement) then the engine driven pump followed by a red cube. I disconnected the fuel line at the servo inlet. Problem is that I am getting no fuel whatsoever as far as the open line. Nothing in the gascolator either. The boost pump is running, but makes irregular noises, something between a click and a clunk. I've got a gallon in each tank, same result on both, regardless of the position of my fuel selector. I tried initially at a 15 degree pitch (as is required for fuel flow tests in Canada) and then again after lowering the nose to ~level. I've got no leaks and can sump fuel out of both tanks.

I'm not sure what to look at now. I'll verify the orientation of the boost pump and the pre-filter, but I don't think that's the problem. Is it possible to wire those backwards?

Anyone have any insight? Maybe help identifying the noise I hear?

Thanks.

Jpm757 · #2 03-30-2018, 01:38 PM

Sounds like your pump is cavitating/not getting fuel. Try putting 5 gallons in the tank. My DAR wanted a 5 gallon measured fuel flow test. Is this a carb or F/I engine. In general these pumps will need a head of pressure to get an initial "prime", especially the low pressure pumps.

YellowJacket RV9 · #3 03-30-2018, 01:50 PM

How long are you letting it run for? You have to listen to it make that awful noise for a bit until it draws the fuel in, unless you can prime the fuel lines up to the pump somehow. I recall mine taking at least 5-10 seconds to prime.

Chris

Flying Canuck · #4 03-30-2018, 01:55 PM

Canadian fuel flow tests are supposed to be done with minimum fuel which is calculated based on engine horsepower. Works out to 1.1 gallons. I can certainly add more fuel to try to get it primed, I'll just need to drain it for the actual test. My engine is an IO-320, Precision Silver Hawk EX fuel injection. My boost pump is a BPM-1. Not sure what's considered a low pressure pump, this one is supposed to deliver 30psi.

Bevan · #5 03-30-2018, 01:55 PM

With the fuel valve on, and fuel line disconnected at the servo inlet, put a small amount of pressurized air into the vent port to very SLIGHTLY pressurize the tank and wait for the fuel to be pushed through the lines to the disconnnected line. I agree you should probably have more than one gallon in the tanks to start with. Start with 5 gallons.

Bevan.

Flying Canuck · #6 03-30-2018, 01:56 PM

Quote:

Originally Posted by YellowJacket RV9

How long are you letting it run for? You have to listen to it make that awful noise for a bit until it draws the fuel in, unless you can prime the fuel lines up to the pump somehow. I recall mine taking at least 5-10 seconds to prime.

Chris

I'm waiting for a good (but not pleasant) 30 seconds on each attempt.

BobTurner · #7 03-30-2018, 02:18 PM

I had the same issue. I assumed the never-got-wet seals weren?t sealing?? Anyway, with the engine side fuel hose disconnected, I just blew thru some tubing connected to the fuel vent until the pump got ?wet?. Then it worked fine. I pumped all the fuel thru and let it sit. Next day it worked okay, no prime needed.

DRMA · #8 03-30-2018, 02:21 PM

Quote:

Originally Posted by Bevan

. . . put a small amount of pressurized air into the vent port to very SLIGHTLY pressurize the tank . . .
Bevan.

Be VERY careful if you do this as you can very easily over pressure the tanks and damage them. Pressure should be no more than a couple inches of water (e.g. less than 1 psi). I believe a safer approach is to add additional fuel to the tanks instead.

David Paule · #9 03-30-2018, 02:49 PM

Probably no issue at all, but is your fuel valve set up so that "on" is really on? Be a shame if it wasn't....

Although I imagine that one tank at least would have flowed if this were the case.

Dave

Flying Canuck · #10 03-30-2018, 05:36 PM

Thanks for all of the quick responses on this. I went back out to the airport armed with those suggestions and quickly had fuel flowing. I added more fuel (to 4 gal) to the right tank and blew some air through the vent line to add some pressure. Worked like a charm. Did the same on the left, but probably didn't need to, that one flowed right away. Got my flow tests done with satisfactory results.

Thanks again, I love this place!