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This scenario is occurring with my TL30 Sirius with a 912ULS

When at altitude with 5200 rpm, fuel pres drops to 2.0-2.1 psi. Problem alleviated by turning on the Aux Fuel Pump...brings the pres into the 4.2-4.8 range. What's odd is that during taxi, run-up and take-off, without using the Aux Pump, the fuel pres does not fall into the 2's. It only happens once I am at altitude. 

Now...after landing and clear of the runway, I turn off the Aux Pump and the fuel pres remains in the high 4's. Plus there a faint smell of fuel.

Question 1: if I am losing pressure with just the mechanical pump due to a fuel leak, where would be the most obvious place to check the fuel circuit. All the hoses were just replaced as part of the 5-year advisory from Rotax. 

Question 2: Prior forum posts advised not running the Aux Pump continuously. Is this what is generally accepted, even when experiencing low pres?

Mark Bearss, Brainerd, MN

 

 

  • Re: Low Fuel Pres w/Mech Pump

    by » one month ago


    What mechanical fuel pump do you have installed?

    Can you provide P/N and S/N?


  • Re: Low Fuel Pres w/Mech Pump

    by » one month ago


    I am the 3rd owner of this aircraft and am unable to locate data on the P/N or S/N's for this fuel pump.

    It has a mfg date of 2009. It is the mech pump located on the prop gear box. I am trying to rule out whether there is a slight leak occurring somewhere due to detecting a fuel odor, and because the hoses were just replaced. So I am trying to determine where in the circuit would I check first for a possible loose connection. My best guess is downstream from this pump. But what does not make sense is the observation of normal fuel pressures when taxiing and the Aux Pump is off.

    Also, the fuel circuit does NOT recirc./return back to the left fuel tank; it goes to a gas-collator. 

    Again, any suggestions will be greatly appreciated.

     


  • Re: Low Fuel Pres w/Mech Pump

    by » one month ago


    The engine requires more fuel at higher RPM and it's not unusual to see fuel pressure drop as flow increases. That said, it should not drop below the minimum of 2.2PSI

    If you smell fuel, then it is likely you have a leak upstream of your fuel pump and this can cause the fuel pump to lose pressure as you are sucking air on the suction side of the fuel pump. We have seen many aircraft return fuel to the gascolator; however, it should return to the fuel tank so vapor can be properly vented and not sucked back into your fuel system. 

    Remember this rule... IF Your fuel pump is GOLD...It's OLD! and must be replaced with a new style grey BCD fuel pump! 

    If you want to check for leaks on the suction side of your fuel system, We suggest you block off one end of the fuel system and place a vacuum pump on the other end. A vacuum pump similar to what you use for bleeding brakes (hand activated). If your fuel system can hold a vacuum then it's solid


  • Re: Low Fuel Pres w/Mech Pump

    by » one month ago


    I thought fuel pumps were a mandatory 5 yr change, if in doubt chuck it out.


  • Re: Low Fuel Pres w/Mech Pump

    by » one month ago


    I will check under the cowling my next trip to the hanger and see what vintage fuel pump is there. Thank you! If my memory serves me, I believe it's gold. Will pour thru the service records, too.

    I will also follow your suggestion to conduct a negative pressure test. I appreciate the feedback. 


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