Fuel Pump Going Out?

[MikeyDale]

I have got 19 hrs in Phase 1 and my mech fuel pump has never missed a beat. Lyc IO360 W/Bendix FI. Burning 12 gph I get 23 psi. Burning 8 gph I get 26 psi. My engine rebuilt 75 hrs ago plus the 19 I put on it. Fuel pump was rebuilt same time as the engine. But, yesterday, I filled up with gas to the very top of both tanks. I took off and flew 30 minutes and landed with no issues. When I restarted after on the ground about 30 minutes, my fuel pressure started fluctuating and engine died. OAT 80. I restarted and taxied out ok without the boost pump. I turned the boost pump on and took off. I climbed out and turned off the boost pump and cruised 1 hr. Back home over my airstrip before desending, I decided to do some stalls. When I came back in with the power after stalling, fuel pressure started fluctuating. Several times later, I made the fuel PSI fluctuate in cruise burning 8 gph making 30deg backs right and left. Tried both tanks, same. I landed. ....De-cowled and checked everything out. Looked good. I took the airflow performance boost pump fuel filter out and blew thru it and it had no resistance. Found two tiny slivers of aluminum cleaning it, otherwise, clean as a whistle..........Cranked up this morning, OAT 73, no boost pump, and after warming up started taxi and PSI started fluctuating! Both tank vents are clean. No other fuel filters....Is there a screen in the Lycoming mechanical pump that could be clogged? Ive never had one apart. Should I go ahead and order a new fuel pump? I've read some threads suggesting a blast tube on the fuel pump in which have not, but fluctuating pressure in the cool morning before taking off rules that out, doesn't it? Thanks in advance.

[aerhed]

Crack the line at your FP sender and purge it. Not saying thats it, just an easy thing to do.

[MikeyDale]

Took off this morning with a little over 1/2 tank of fuel on each side. Flew for two hours and the mechanical pump never skipped a beat. Landed and filled up, took off , and here we go again. Fuel PSI started fluctuating! Landed and pulled up to my hanger and had to hit the boost pump several times to keep the engine running at a idle. I'm wondering if fuel is getting in my tank vent lines when I fill up causing this or is my mechanical pump getting weak?

[Walt]

I would suggest inspecting the entire fuel system from the selector valve foward for leaks (any sign of a blue stain means a leak) and that all fittings are tight. Verify that there are absolutely no restrictions from the selector valve to the fuel pump. look closely (internally) at flex lines, fuel flow xdcr or anything else installed in the feed line.

Verify both tank vents systems are clear (fuel in the vent lines will not cause fuel starvation but clogged vents will).

If none of the above reveals anything, I would replace the pump before further flight.

[MikeyDale]

Thanks Walt. I'm going to work on it.

[Pmerems]

Could it be a vapor lock issue? What does your fuel plumbing look like FWF? Where is your fuel flow sender mounted? Just thinking outside the box.

[MikeyDale]

I thought so to but a couple of mornings ago, I started up and while warming up, fuel pressure fluctuated a few times. I'm going to go thru everything first to make sure the mech pump isn't getting air from somewhere.

[Steve Melton]

how to pressure check connections downstream of the fuel selector and upstream of the pump? on the ground, select any tank, turn on pump, note fuel pressure rise, then select fuel off, turn off pump. this should raise the pressure on all lines back to fuel selector. let it set overnight and check for blue stains. I don't know if this would work for fuel injected.

[BillL]

Originally Posted by MikeyDale

I thought so to but a couple of mornings ago, I started up and while warming up, fuel pressure fluctuated a few times. I'm going to go thru everything first to make sure the mech pump isn't getting air from somewhere.

Probably a good idea. I have taken a pressure gage and made a test setup to pressurize the fuel system from the extremes. I think from mechanical pump inlet back to the bulkhead connector at the wing root is as far as it can be connected. I take air pressure at 30 psi, pressurize and shut off the valve. Then watch the pressure. It should not drop - at all. Maybe 1/2 psi overnight, and that is with no fuel in the lines, just air. I found leaks on my 7 and my friend found a leak in his boost pump. The factory assembled part.

IT does not take much hardware. I use kids bubble juice for finding the leak.

Good luck!

Edit: To confirm, you are using 100LL? Not living dangerously with auto gas are you?

[MikeyDale]

To confirm, you are using 100LL? Not living dangerously with auto gas are you?

The last time I had PSI fluctuations, I had 1/2 100LL and 1/2 auto gas (No Ethanol) in one tank and all 100LL in the other. I had the same PSI fluctuations from both tanks swapping back and forth.