Air in fuel lines

[Mike Vinci]

I recently started catching air in my fuel system.  All component of the fuel system are less than five years old (tanks, lines, valves,etc)  The Racors were not catching air but the secondary filter on the engine was.  The fuel filter would be down quite a bit on the secondary.  To try to narrow things down I bypassed the secondary, changed the primary to a small micron, and ran the motor.  I don’t seem to be getting air anymore.  My throughs are possibly a hairline crack in the filter assembly, or I am using the wrong filter.  I did take the two hoses on either side of the secondary filter along with the filter and assembly itself and pressure test it and spray it down with soap.  I know the system is normally under vacuum not pressure but figured its worth a shot.  Below is a picture of what model QSM11 I have along with the filter im using.

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[pwrobert]

Additional next steps

Tony helped me out to find leaks in my Sarboard fuel lines fairly recently.  

He had me make up sections of clear vinyl hose with the proper malefemale fittings to fit in your fuel lines.  Can be done one by one or a couple at a time depending on how many hose segments you have.  I had several as I had a Maretron FFM100 between the tanks – filters-and engine last chance filter. So I typically had 3 clear pieces.  One before all the filters, one after the last filter and one after the FFM100 between it and the on engine filter.

I recommend getting the vinyl hose that is not the real thin type as it dooes not seal snugly to the brass fittings.  Do not use that with reinforcement mesh in the vinyl – it makes it too hard to see fine bubbles. Even with that I put a clamp on each tubinig commection with sealer on the barbs.  (ask me why if you must but trust me it is necessary as vinyl hose is not as elastic and tight to fittings as rubber or silicone hose is).  I bbought Press-Lock fittings and used PEX clamps with Permatex Gasket maker for it’s sealer but you can do that how you want.  I’ve kept and stored the clear hoses with their fittings in my spare parts box at home in case of futere need to track down an issue again.

Re-prime the engine filters and let the system run for a few minuts to get out any residual bubbles and see which junction is the first to show bubbles.  That’s your leaking fitting or hose.

If it shows bubbles in the first segment before the filter(s) then you have to think about your pickup or any manifold fitting or valves between the tank and filter(s)..  

If there are no bubbles in any segments then it has to be in the filter or it’s fittings.

All you would start out with is Segment A and Segment C most probably.  Or worst case scenerio ones leading fom tank (unlabeled) or just before hose G.  All the rest of the stuff in diagram is for my fuel flow analyzer testing.

[Tony Athens]

QSM11 On-engine fuel filter

All you can do is eliminate possibities one-by-one.. New Fleetguad filter ( install twith he oil/grease on the top gasket. Or maybe pressure  the sysem at about 15-25 PSI?

All Fittings out and all reinstalled with sealant ( I like Rectorseal 5 for these  style of fittings) , a very close casting inspection? 

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