Fuel pressure needle gone wild!

[Joe Larussa]

Ive been messing with my fuel pressure gauge for about six months. Needle vibrates like a big dog. If I drain the fuel in the hose that comes from the inside firewall to the gauge it's perfect for a few flights then back to crazy town. I do have the sniffer on the back of the gauge that's supposed to dampen the needle vibration. Here's my thought. Could you put the sniffer gizmo on the other side of the firewall to help fuel from entering the hose on the inside of the cabin and possibly stop the banjo? 

[N201MKTurbo]

Take the hose off of the servo and the gauge. Blow it out with compressed air To get all the fuel out.

That should fix it for another decade.

Are there any fuel stains in the cockpit? If it leaks any air, the fuel will fill the line back up.

[Joe Larussa]

I have drained all the fuel out but never used compressed air.

[N201MKTurbo]

Did you drain it all the way back to the servo? You said that you only drained it back to the firewall.

[Joe Larussa]

Just now, N201MKTurbo said:

Did you drain it all the way back to the servo? You said that you only drained it back to the firewall.

Drained from servo all the way to the gauge. Always seems to come back.

[N201MKTurbo]

Well, there must be a tiny leak somewhere that is letting the air out and allowing the fuel to replace it.

[Guest]

7 hours ago, Joe Larussa said:

Ive been messing with my fuel pressure gauge for about six months. Needle vibrates like a big dog. If I drain the fuel in the hose that comes from the inside firewall to the gauge it's perfect for a few flights then back to crazy town. I do have the sniffer on the back of the gauge that's supposed to dampen the needle vibration. Here's my thought. Could you put the sniffer gizmo on the other side of the firewall to help fuel from entering the hose on the inside of the cabin and possibly stop the banjo? 

Joe,

Normally the fitting at the fuel servo finger screen is the restricted one. Also clearing the line of all fuel is sufficient to steady the needle.  There must be a small leak at the gauge or firewall fitting.

Clarence

[mooniac15u]

I know most of the vintage Mooneys had a fuel line all the way to the gauge but I thought all the M20Js had electronic fuel pressure gauges with transducers on the other side of the firewall. Do you have the old style of gauge?

[jetdriven]

19 minutes ago, mooniac15u said:

I know most of the vintage Mooneys had a fuel line all the way to the gauge but I thought all the M20Js had electronic fuel pressure gauges with transducers on the other side of the firewall. Do you have the old style of gauge?

they didnt replace the mechanical fuel pressure gauge until early 1978.   mine is a 77 it still has the mechanical gauge and accompanying fuel hose behind the panel.

[Joe Larussa]

2 hours ago, mooniac15u said:

I know most of the vintage Mooneys had a fuel line all the way to the gauge but I thought all the M20Js had electronic fuel pressure gauges with transducers on the other side of the firewall. Do you have the old style of gauge?

I do have the old style gauge with braided hose going all the way to the back of the gauge unfortunately.

[KSMooniac]

My '77 J was the same as well...until getting replaced with an EDM-900 and removing those fluid lines coming into the cockpit.  

[carusoam]

Hot oil and fuel being delivered to the cockpit with unknown leaks in the system...

JPI and a couple of other players have various solutions.  You get better data and less chances of hot or flammable fluids delivered to you co-pilot's knees.

Best regards,

-a-

[N201MKTurbo]

Well, at least if it leaks inside you will know about it. 

Try to cut through one of those hoses with anything less than an abrasive cut off wheel. 

There are a lot of better things to lose sleep over.

[jetdriven]

A few people have had those hoses suddenly start leaking, due to age mostly.  One was a poster on here.  Another was my lawyer.  Both suddenly started dumping tons of fuel inside the cockpit.  Luckily the guy I know was taxiing.  The Poster on here cut the fuel selector off to stop the leak and glided to a runway. I chickened out as replaced mine for the 100$.  It was date coded 1976. 

Edited April 6, 2016 by jetdriven

[mooniac15u]

I had that line start leaking in my M20D. The line got kinked during some avionics work and that led to a crack. My CFII noticed the 100LL dripping on her leg while we were taxiing. I seem to recall that it was some kind of rigid line rather than a braided line. The braided hose sounds like an improvement.