260c fuel pump output

[Joe Greene]

I've got a 260c that has been hesitant to indicate fuel flow during the engine priming procedure. It used to have no issue indicating the 4gph but now usually seems to show 0gph while operating the dukes electric fuel pump. I'm not certain if it is an indicator issue or low pump pressure issue.. According to the service manual, the dukes pump should pump 50g/hr @14 psi... I attached a length of hose and pressure gauge to the fitting on the forward side of the firewall (smaller fuel line with adapters, t-fitting, elbow,). At the end of my test rig I placed a small ball valve to adjust the out flow and achieve the 14psi. The no flow test yielded 22psi, and the 14psi flow test yielded 35.6 Gph. (Filled a 1 gallon jug in 1:41sec). Does anyone here think this would be an accurate test, or are the numbers specified in the service manual based on a bench test (14v, pressure guage mounted directly to the pump, and short straight test line for flow? I'd hate to replace the pump only to get the same performance out of a rebuilt unit!

[Clarence Beintema]

Your test method sound accurate enough. I recently had a Pump repaired at Aeromotors LLC. Good price and turn time. They may be able to offer advice.

Clarence

[Joe Greene]

Pa24-260c..... I sent out the fuel flow indicator to century instruments, they did an overhaul on the unit and stated that it had a loose "sector"? Reinstalled with no change in indications. I proceeded to send out the Dukes pump to Aeromotors llc in brown town Wisconsin, 400.00 (rebuilt pump end, as well as new brushes and armature. The pump now seems to sounds stronger and I am quite sure it is performing better! However, now I still do not always achieve the 4gph on initial pre-start prime. (Only tested a few times so far). I also think the in-flight fuel flow indication is a bit low (overhauled original indicator), showing just shy of 12gph @ 3500ft, 71f oat, 22mp-2300 rpm, aprox 100 deg rich of peak on stock egt. I would think it should be closer to 14gph.. A timed test flight this weekend may help confirm actual fuel burned. Cleaned and inspected all lines to the fuel flow indicator, as well as the flow divider. Checked for air bubbles at the firewall too. I also did a 3 minute leak check on the fuel servo, by capping the output, with not so much as a drip produced from the intake drain. I am wondering if the flow divider could be internally "tired" so to speak, it is nowhere near new but looks clean? The plane runs normal as well. I do seem to get a puddle of fuel on the ground if I wait for the 4gph to show while priming, how normal is this in others experiences?

[Zach Grant L1011jock]

There is nothing magical about a 4gph flow rate to prime the engine. Running the pump with a full rich mixture will send some fuel from the fuel fuel servo to the flow divider, at a certain flow rate there will be a certain pressure based on the back pressure of the fuel nozzles. If the flow rate from the servo to the divider is less, the pressure will be less, but the fuel will still flow thus flooding the engine and allowing a puddle of fuel to form under the engine as it runs down the intake risors and out of the sniffle valves, if the pump is run for an excessive period. If the pump is putting out proper pressure, and the gauge is reading correctly, what is between the two is the metering valve of the fuel servo (throttle body). If it gets fuel and starts, everything is just fine! If you really want to know what you are burning, invest in a true fuel flow instrument that uses a flow transducer, not a pressure gauge marked in GPH. A JPI FS450 is very economical in the great scheme of things, easy to install and worth it's weight in gold as both essential information and as a diagnostic instrument.

Zach

[Joe Greene]

Thanks for the reply. I agree with most of what you said! I am actually trying to chase down what has recently changed in regards to my priming indication and fuel flow indication in flight. A modern fuel flow or engine anylyzer would be a nice upgrade no doubt, but regardless of the equipment installed I need or would Atleast like to determine what has caused the recent change. I have learned a lot about these aircraft from this forum, and figure this experience may help someone else here down the road!