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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
> --
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