What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel smell, boost pump

M

Mike Coady

Well Known Member
Ok builders, need some info on this one. When I run my boost pump, I'm getting a fuel odor. But, I've uncovered everything to check for Leaks and there are not. Is it normal to smell, is pump venting some how?
 
Mike Coady said:
Ok builders, need some info on this one. When I run my boost pump, I'm getting a fuel odor. But, I've uncovered everything to check for Leaks and there are not. Is it normal to smell, is pump venting some how?
Click to expand...

Assuming the smell is in the cockpit, high probability there is a leak. This also means it would suck air with the boost pump off and could result in loss of engine power.

If smell is FWF, and the engine is fuel injected, it could be from loading the cylinders with fuel. Not good. Washes them free of oil. Be careful.
 
Last edited:
Fuel smell

In addition, the engine is running fine, no onomalees. When I switched tanks, I used fuel pump as recommended and I got a definite wiff of avgas in the cockpit while flying. I tested it on the ground as well and also got a wiff. I uncovered my lines in the floor and can see nothing there or around the fuel pump itself.
 
must be a leak somewhere. Check the fittings. I had a bad flare at the valve that caused a leak. Did all my fuel flow calibrations before ever noticing it.... Meaning I put about 10 gallons through that pump before noticing. Deffinately had better fuel flow after fixing it too because no longer any cavitation. Unhook the fuel line at the carb and pump some fuel through, it should be a strong steady flow, no air or gurgling.
 
Fuel smell = fuel leak... keep looking until you find the source.
Airplane should be grounded until you do.
 
Check here at the gascolator and on the other side. It happened during Phase 1 when aux pump was running.


 
put a wrench on every fitting in the fuel system. Start with the easy ones. Which fuel valve? check the stem on the valve.

Just my $2 worth. [Yes, I meant 2 dollars] Pennies need to be phased out. ;)
 
Walt said:
Fuel smell = fuel leak... keep looking until you find the source.
Airplane should be grounded until you do.
Click to expand...

Yep.

I had a fuel smell that was very faint but bugged me. I discovered it when I checked the vent lines. There was some blue residue that collected at the bottom of an AN bulkhead elbow which revealed the source. Another 1/8 turn fixed it. It was the right side 90 degree bulkhead fitting (see picture):
http://www.aclog.com/rv-9a/images/Fuselage/DSC_0049.JPG
 
Easier to find leak by LIGHTLY pressurizing tanks and isolating sections of the fuel lines with the tank valve. Tanks can be pressurized by removing cap and cutting out the valve from an inner tube along with a small square from the tube itself. Tape that up over the cap hole and pump air in with a bicycle pump. Set up a manometer with some clear tubing attached to the fuel vent lines so you can keep an eye on the pressure. Don't go over 1 or 2 psi. Then check for leaking fuel! Sometimes just running the fuel pump won't result in an obvious leak of liquid fuel if it's a small leak, but your nose doesn't lie.

erich
 
Fuel

Ok thanks Walt and vlad. It's only when I flip low pressure boost om. I'm think it has to be from pump to gascolator. I'll keep looking
 
The fuel evaporates but the blue dye does not. Rub your fingers around each of the connections - any residual dye will stain your fingers at a leakage point. The leak may be obscured from view even with inspection mirrors.
This method worked for me when I had a feint smell only when I first rolled the canopy back after several non flying days.
 
I had a smell of fuel after a flight that turned out to be the main fuel fitting going into the carb. We had the carb off for rebuild and had about 10 hrs on the Plane after reinstalling the carb. When the boost pump was on we were spitting fuel out the fitting. Removed the fitting installed fuel lube on the fitting and reinstalled and it has been fine for offer 200 krs. I really smelled it when I opened the oil door for cooling.
 
Doug said:
The fuel evaporates but the blue dye does not. Rub your fingers around each of the connections - any residual dye will stain your fingers at a leakage point. The leak may be obscured from view even with inspection mirrors.
Click to expand...

+1. Take a clean white tissue and wipe down each fitting and you will find the leak. Be careful of over torquing the fittings, you can easily damage the flare.
 
drill_and_buck said:
+1. Take a clean white tissue and wipe down each fitting and you will find the leak. Be careful of over torquing the fittings, you can easily damage the flare.
Click to expand...
Second this. Also, if you don't find a loose fitting, you really should take them all apart and look for cracked or damaged tubing flares. If you don't find one. Start inspecting backward toward the tanks.
 
Fuel thanks

Thanks all! I'll find it one way or another using all you sound advice. I'll try to post my results here in the next week sometime. Right now, it's to darn cold in the hangar so it'll be a few more days.
Thanks again,
Mike
 
Fuel leak

Well, after a littLe vigilence and contorting my big body in under the panel, I uncovered all my fuel lines and finally found my fuel leak. Thanks for all the tips! As it turns out, the culprit was exactly what Vlad had posted for me. It was the 90' AN fitting that goes through the firewall and doubler into the gascolator! The fitting was not completely tight and it could have used a bit more sealant. I replaced it and since I was able to tighten it another quarter turn, I had to remanufacture a new fuel line from the boost pump to the gadcolators elbow fitting. The fuel did not leak to sighting for about fifteen full seconds of running the boost pump so it was a slow leak. And, since it was behind the doubler, it took it a while to show itself. I'm very glad to have stuck with it and finding it. Thanks to you all for taking the time to give advice and pics! Back in the air for N771MK!
 
Just a note that takes an absolutely microscopic amount of fuel to stink. It might all be evaporating so you can't see it. Not sure if there is a way to make a stain visible or not. Perhaps some grey haired a&p member would have a trick up his sleave? Like wrapping a kleenex with a tiewrap around various joints, then running the pump and checking for stains? Of course you don't want to go flying with gas soaked paper in the cockpit...duh.

On my airplane I put seal lube on all the npt fittings (not flare fittings) and no more issues. It's one of those sticky goos that never cures.

So it's leaking - the extra pressure with the pump is sqeezing it out a tiny hole. Just gotta track it down.
 
sblack said:
Just a note that takes an absolutely microscopic amount of fuel to stink. It might all be evaporating so you can't see it. Not sure if there is a way to make a stain visible or not....
Click to expand...
The blue dye, assuming you're using 100LL, does just this. Fuel evaporates, dye remains.
 
You must log in or register to reply here.
Back
Top