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Scott:
I just read your response and I believe you may have nailed my problem. At the very least you have given me a good procedure to check what I believe to be the culprit...air leaking into the fuel system via the fuel selector valve.
I will let you know how I make out.
Thank you!
Sent from my iPad
Berni Breen
Bbreen@cableone.net
On May 15, 2011, at 7:48 PM, Scott E Keighan <scottekeighan@sympatico.ca> wrote:
> I had the exact same issue 2 years ago. It took me 6 weeks to finally track down the problem.
> I did the same things as yourself as in dismantaling the engine driven fuel pump, took the entire fuel system apart from the engine
> pump to the injectors, checked all the fittings and connectors from the tanks to the engine etc.
>
> An auto mechanic told me how to find the problem, vacuum not pressure. Lots of time a system will hold pressure but not
> a vacuum.
>
> My issue was a broken o-ring on the fitting for the electric fuel pump (got old and brittle). Air was being sucked into the
> system via the broken o-ring. This is what you do to check for this. Go to Harbor freight and get a
> hand pump vacuum pump (around $29). Remove the fuel line at the engine fuel pump and make
> a fitting that will work with the vacuum pump. Place your fuel valve to the off position. Try to get some
> of the fuel out of the line by the vacuum pump as the fuel will ruin the diaphram at the pump (i learned this
> the hard way). The pump will hold a vacuum if everything is ok. If there is a leak start to disconnect fittings
> and cap them off between the fuel selector valve and the pump to determine where the leak is.
>
> Another check is to run the electric fuel pump with the mixture at idle cut off. Have enough fuel in the tanks to cover the
> fuel return ports in the tanks. If you hear bubbles in the tank then air is getting induced into the system. (mine did this also).
>
> Good luck
> Scott Keighan
> LIV
>
>
>
>
>
> > To: lml@lancaironline.net
> > Date: Sun, 15 May 2011 08:04:47 -0400
> > From: bbreen@cableone.net
> > Subject: [LML] Fuel restriction or air?
> >
> > I have been trying to chase down the cause of a fuel issue in my normally aspirated Lancair IV engine. During a cross country flight my fuel flow indicator began to show fluctuations which I mistakenly believed to be false readings. Shortly thereafter during the same flight the engine began surging, slightly at first but increasingly worse in short time. So much so that I began to plan for an emergency landing as I was looking to find the cause and to introduce a remedy. I turned on my electric (back up) fuel pump and the engine immediately began to run strong and the fluctuation readings stabilized.
> >
> > After gaining altitude I turned off the electric pump and the unstable fuel flow readings as well as the engine surge returned.
> >
> > My initial take was that my problem was caused by a failing engine driven fuel pump. Even with that belief (once back on the ground) I checked as much of the fuel system as possible looking for potential restrictions. I looked at and cleaned the screens at the wing root connections as well as the inlet on the GAMI injectors. I found no restrictions so I removed and exchanged my engine driven pump for a rebuilt unit.
> >
> > After installing the rebuilt pump the engine tested fine on the ground and fine in the air on a subsequent cross country trip. Approximately 2.1 hours of flying time later the exact same symptoms returned...erratic fuel flow readings followed closely by engine surge.
> >
> > I am now at a loss as to what I should now look for. Could my problem be due to air somehow being introduced into my fuel flow? Should I be looking at my fuel selector as a possible culprit? If so how would I test that possibility?
> >
> > Any and all suggestions would be most appreciated.
> >
> > Sent from my iPad
> > Berni Breen
> > Bbreen@cableone.net
> > --
> > For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
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