Fuel Pressure gauge issue

[J. mitchell]

I am experiencing fluctuating readings in my fuel pressure gauge when taking off. On the ground I get normal readings but on departure in the climb the gauge sometimes falls to zero yet my digital fuel flow gauge indicates no problem. Once in level flight the pressure returns to normal readings. Any thoughts on this issue?

[rocketman]

Check the ground connection

[RobertGary1]

Check the ground connection

 

Ground? Unless your pressure gauge is very different than mine there is just a fuel hose that runs into the back of the instrument. 

 

-Robert

[mooniac15u]

The newer models use a pressure transducer on the engine side of the firewall with wires to the gauge.  The older models, such as the C, have a fuel line into the back of the gauge.

[RobertGary1]

The newer models use a pressure transducer on the engine side of the firewall with wires to the gauge.  The older models, such as the C, have a fuel line into the back of the gauge.

Are you sure? As this is a pre-J forum and I have one of the last F models produced, I'm not sure that is true. Mine does not use a transducer. 

 

-Robert

[mooniac15u]

By "newer" I meant J and later.  I know this is a pre-J forum but I'm guessing Rocketman probably has a Rocket.

[Alhall]

Had to replace that fuel pressure line on my M20C last year. Started leaking fuel and dripping on the exhaust pipe. It was old and deteriorating.

[mooniac15u]

I had to replace the line in my M20D when it started leaking on my CFI.

[RobertGary1]

I just replaced mine as well. Scary to think of fuel spaying around in flight.

[Marauder]

I just replaced mine as well. Scary to think of fuel spaying around in flight.

I went one step further on my F.

From this:

To this:

[FloridaMan]

My line started leaking too and I had it replaced last annual. It set back the timeline and I had to fly commercial to get to work. I have an EDM-900 on order at the moment. If I counted correctly, I have 11 engine instruments that are nearly 50 years old that the EDM-900 replaces. No only will it give me more and better information, if a sensor fails I won't go having to track down somebody who has an old worn out instrument on the shelf. 

[ArtVandelay]

My line started leaking too and I had it replaced last annual. It set back the timeline and I had to fly commercial to get to work. I have an EDM-900 on order at the moment. If I counted correctly, I have 11 engine instruments that are nearly 50 years old that the EDM-900 replaces. No only will it give me more and better information, if a sensor fails I won't go having to track down somebody who has an old worn out instrument on the shelf.

Doesn't it used the existing fuel sensors (2 in each tank), so that wouldn't be true in this case?

[Marauder]

Doesn't it used the existing fuel sensors (2 in each tank), so that wouldn't be true in this case?

The floats can be serviced but having someone service the actual gauge is a little harder.

[FloridaMan]

I was thinking more along the lines of the tach, mp, oil temp/pressure, alternator, cht/egt -- the instruments that can give you advanced warning of impending engine failure. With the fuel flow and totalizer, I would have triple redundancy on fuel level with the in-tank and wing mounted gauges, the least trustworthy being the sensors in the tanks.

Sent from my iPhone using Tapatalk with autocorrect fucking up my posts.

[J. mitchell]

I appreciate all the responses to my question about the fuel pressure gauge reading. There doesn't appear to be any fuel leaking from the line going to the gauge and when the electric fuel pump is on pressure is right up there, but when the switch is turned off the pressure falls to zero or close (my E.I. fuel flow gauge indicates the fuel is flowing just fine) and then gradually recovers as I transition to cruise. So, thanks again for the comments.

[Marauder]

I appreciate all the responses to my question about the fuel pressure gauge reading. There doesn't appear to be any fuel leaking from the line going to the gauge and when the electric fuel pump is on pressure is right up there, but when the switch is turned off the pressure falls to zero or close (my E.I. fuel flow gauge indicates the fuel is flowing just fine) and then gradually recovers as I transition to cruise. So, thanks again for the comments.

Boy! Did this thread go wandering. I thought I was responding to a leaky fuel gauge issue.

If your plane is an F or older model, I would verify that you don't have some sort of crud in the line at the gauge side. It sounds like you can build full pressure.

The gauge itself could be beginning to fail. Sorry for the wandering. What fuel/manifold pressure gauge do you have? Like the one I posted above?

[Marauder]

If it is the gauge, I think you mentioned you have an EI fuel flow gauge. If it is a FP-5L, you can buy the fuel pressure transducer for it and use it a primary gauge.

[mooniac15u]

when the electric fuel pump is on pressure is right up there, but when the switch is turned off the pressure falls to zero or close

 

The fact that his happens when you switch off the electric pump is a key piece of information.  The fuel pressure gauge in my M20D behaved this way too.  I seem to recall another thread about this where several others saw the same behaviour.

[mooniac15u]

http://mooneyspace.com/topic/13291-fuel-pressure/

[Alhall]

The line going to the instrument has a small orifice at the fitting. Would be easy to have a restriction at the beginning of it.

Al

[J. mitchell]

Once again, thanks for all the input. Yes, the gauge is an older gauge with a small fuel line going to the back of the gauge. I can build up pressure with the electric fuel pump on, but once switched off and as I climb the pressure falls and then begins to climb once in cruise. The E.I. Digital gauge is the one pictured in one of the comments (Marauder) above and that indicates a good fuel flow, so I am not concerned that I am going to run out of fuel. I will check out your recommendations.

[RobertGary1]

The line going to the instrument has a small orifice at the fitting. Would be easy to have a restriction at the beginning of it.

Al

Perhaps on the instrument itself but not the line. The fittings are standard ms-24590-3. I've got some old ones I'm looking at right now.

-Robert

[Alhall]

Robert

I was talking about the line from the carb to the firewall. I'm pretty sure mine had an orifice fitting at the carb. Who knows I could be wrong.

Al