Cherokee 140 Fuel Pressure gauge sporadically high

[John Tyrone]

Hello,
I'm a flying a 1969 Piper Cherokee 140 "C" that is having a strange issue with the fuel pressure gauge. Usually the gauge will read in the mid-green with engine running and high green (or slightly above green) with electric pump on. Rarely, with or without electric pump, gauge will peg to the far right. Later it will correct. I can't find any contributing factor and it seems to be unrelated to on/off of electric pump. Mechanic bleed lines with no real improvement. Any suggestions? Thank you.

 

[Bell206]

Any suggestions?

The only thing I can add is most indicators will usually full scale (peg) if it loses the voltage/capacitance signal or grounds out. So a loose/chafed wire is possible as are a number of other things.

 

[mondtster]

It’s been a while since I’ve had to look at an older Cherokee but I believe the 140 should have a mechanical gauge. Of course this assumes we’re discussing the original instrument.

If it does it regardless if the boost pump is on or off I’d be tempted to try a different fuel pump since all the fuel goes through it.

 

[charlie]

A blockage in the crankcase breather will cause high crankcase pressure. The AC pump is vented to the crankcase so the case pressure can raise the fuel pressure high enough to the point where the float bowl overflows which will cause the engine to quit. There should be a scarf cut "whistle" in the aluminum breather tube to prevent this.