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Low fuel pressure


BaldEagle

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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...

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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.

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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).

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