BaldEagle Posted September 9, 2019 Report Share Posted September 9, 2019 Came back from a cross country this morning: fuel pressure was fine (at the white reference mark near the top of the green arc on the gauge), stopped for lunch, and the rest of the trip the fuel pressure was at 14 psi at the bottom of the green arc. Turning on aux boost pump did not increase the pressure. If my mechanical fuel pump is failing, surely the boost pump would increase the pressure? Clogged fuel screen? Wondering how I can troubleshoot this... Quote Link to comment Share on other sites More sharing options...
Browncbr1 Posted September 9, 2019 Report Share Posted September 9, 2019 With engine off and mixture cut off, run aux pump to build pressure. Turn off aux pump and watch pressure. It should hold. Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 9, 2019 Report Share Posted September 9, 2019 Check gauge first... if one pump was dying, the other would have shown an improvement... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted September 9, 2019 Report Share Posted September 9, 2019 6 hours ago, BaldEagle said: Came back from a cross country this morning: fuel pressure was fine (at the white reference mark near the top of the green arc on the gauge), stopped for lunch, and the rest of the trip the fuel pressure was at 14 psi at the bottom of the green arc. Turning on aux boost pump did not increase the pressure. If my mechanical fuel pump is failing, surely the boost pump would increase the pressure? Clogged fuel screen? Wondering how I can troubleshoot this... What kind of FP sensor do you have? The previous owner had an EI sensor installed with a primary (for fuel pressure) FP-5L. I just had the sensor fail with pretty much the same symptoms--FP would read about 14-17 psi and turning on the electric pump only increased it 2-3 psi. When I turned the electric pump with the motor off, it would still only read 17 psi. Obviously, though, if you have the factory fuel pressure gauge, this may not apply. What pressure does your gauge show when the engine is off and mixture closed? If it is a partial obstruction, it should show 25-30 psi because there is no flow to restrict. If it is a sensor/gauge problem, it will show low as well, assuming you don't have a simultaneous engine and electric pump failure. Quote Link to comment Share on other sites More sharing options...
BaldEagle Posted September 9, 2019 Author Report Share Posted September 9, 2019 I have the original factory gauges (cluster). I'm going to swing by the hangar after work to try the above described by @Browncbr1 to see if I can rule out an issue with the engine driven pump. The electric pump sounds strong when priming. I have a feeling that it may be a gauge issue because the needle on the oil pressure gauge (same cluster) sometimes bounces off max with the engine not running (bad ground). Quote Link to comment Share on other sites More sharing options...
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