Monday, July 31, 2017

Fuel Pump Failure

End of June I wanted to depart on a breakfast flight to Benson with my wife, when ~3 minutes after take-off the cockpit quickly filled with a strong stench of gasoline. It wouldn't pass for a minute or two and I knew what that meant.
I turned around and climbed to 10,000 feet. Once over the field I turned off the electric fuel pump and watched the fuel pressure drop quickly to 0.2 PSI when the engine started running rough. I turned the electric pump back on and landed the plane, canceling our breakfast plans. Apparently the diaphragm on the engine-driven fuel pump had ruptured and leaked gas out the weep drain and overboard. At just 207 hours, that's rather frustrating.

out comes the old one....

It didn't take too much time replacing the pump, besides the inaccessibility of course. With crow's feet it's pretty impossible to put any controlled torque on the bolts and that includes the fuel distributor block.

... and in with the new one.
I did an extensive engine ground run at full throttle with only the engine-driven pump running to see if it was working alright. Then I headed for a test flight, steep take-off staying over the field and climbing to 10,000 ft.. Stayed there for 20 minutes before moving away, always staying in gliding range.
Without the electric pump running, the fuel pressure was oscillating between 2.6 and 3.4 PSI. I never saw that with my previous pump. It was a very repetitive oscillation pattern, almost rhythm-like.
Even on a cross country flight a week later I could still see this oscillation pattern but it never dropped below 2.6 PSI.
After coming back from Oshkosh (flying commercial) I had another flight where the mechanical pump produced rock solid 3.9 PSI. No oscillation and no jumps. Apparently, a new fuel pump does need some break-in period.

Let's see how long this one will last. Fingers crossed!

I'll disassemble the old pump to verify the failure mode of a ruptured diaphragm and I will update this post when I have the pictures.