Fuel pressure gauge pegged high

[PTK]

Here's a fuel pressure gauge question. Before engine start when I switch on the boost pump the OEM fuel pressure gauge indicates needle movement and normal pressure. At engine start it pegs high. All along I've thought it was the gauge and lived with it since I back it up with the EDM. My question is is it possible that it's not the gauge but the engine driven fuel pump set too high? Does it even have an adjustment? My fuel flows are normal. I see 18-19 gph on takeoff at sea level.

[mooniac15u]

32 minutes ago, PTK said:

Here's a fuel pressure gauge question. Before engine start when I switch on the boost pump the OEM fuel pressure gauge indicates needle movement and normal pressure. At engine start it pegs high. All along I've thought it was the gauge and lived with it since I back it up with the EDM. My question is is it possible that it's not the gauge but the engine driven fuel pump set too high? Does it even have an adjustment? My fuel flows are normal. I see 18-19 gph on takeoff at sea level.

It might be the pressure transducer. Mine exhibited exactly those symptoms and replacing the transducer fixed it.

[PTK]

14 minutes ago, mooniac15u said:

It might be the pressure transducer. Mine exhibited exactly those symptoms and replacing the transducer fixed it.

Would that explain the gauge indicating normal with only boost pump on? i.e. engine not running?

[mooniac15u]

14 minutes ago, PTK said:

Would that explain the gauge indicating normal with only boost pump on? i.e. engine not running?

The pressure transducer is basically a variable resistor. When the engine is running the mechanical pump outputs a constant pressure and the transducer tends to sit in one spot for long periods of time which seems to wear that spot out. The boost pump probably generates slightly lower pressure so the transducer doesn't quite hit the dead spot.

I also suspected the gauge but replacing the gauge made no difference. Replacing the transducer fixed it.

[Alan Fox]

The Pressure transducer is a very common failure ,   Less than 100 if you know how to buy it..

[mooniac15u]

http://www.aircraftspruce.com/catalog/appages/pmaprod-mooney.php

$146.75 if you want a PMA'd unit.

[1964-M20E]

Check the transducer it might have a piece of foreign matter in there.  Mine was acting up and pulled it flushed the line and cleaned the sensor and now it is working fine.  I still have a new one arriving today.