What is the expected Fuel pressure range for an M20E

[McMooney]

Hello Mooneyspace,

 

my mechanics noticed the fuel pressure for my mooney rarely budges from approx 25psi; only changes when off or the electric fuel pump is on( 27 psi ).

is this the correct behavior?  I've always assumed it was normal.

 

Edited September 2, 2020 by McMooney

[carusoam]

Hey McM!

Sounds good to me...

We want the electric FP to do the same job as the mechanical pump, in case one fails...

At the same time, when using the electric pump... we don’t want it to over supply the engine...
 

Does your FuelP have a green arc on it?  Does the needle stay within the green arc?
 

Some new fuel pumps came out recently, that were over pressuring the fuel by a few psi... there is a solution for that too...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[McMooney]

2 minutes ago, carusoam said:

Hey McM!

Sounds good to me...

We want the electric FP to do the same job as the mechanical pump, in case one fails...

At the same time, when using the electric pump... we don’t want it to over supply the engine...
 

Does your FuelP have a green arc on it?  Does the needle stay within the green arc?
 

Some new fuel pumps came out recently, that were over pressuring the fuel by a few psi... there is a solution for that too...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

Yes, stays within the green arc.  The mechanic seems to think the fuel pressure should vary a bit more and is suspect of the gauge.

[carusoam]

50 year old gauges can benefit from getting OH’d every half century or so... ?
 

FF instruments do a good job of supply back-up info...

JPI 900s and the like are always something to consider for a nice forever plane....
 

Standby for other MSers with a more direct experience...

PP thoughts only...

Best regards,
 

-a-

 

[RLCarter]

Mine was about the same, installed a new mechanical fuel pump and now it’s at the top of the green and stays there. Needle might wiggle  some with RPM or Boost pump on, but it isn’t much

[charlesual]

Hey McM!
Sounds good to me...
We want the electric FP to do the same job as the mechanical pump, in case one fails...
At the same time, when using the electric pump... we don’t want it to over supply the engine...
 
Does your FuelP have a green arc on it?  Does the needle stay within the green arc?
 
Some new fuel pumps came out recently, that were over pressuring the fuel by a few psi... there is a solution for that too...
 
PP thoughts only, not a mechanic...
Best regards,
-a-

Mine stays at the top of the green. Can/Should that be adjusted?


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[Hank]

I'm happy if the fuel pressure in my C stays in the green. Never heard that a constant or near-constant fuel pressure was bad, I always thought that was the goal . . . . 

[takair]

Mine sits around 25 almost all the time.  Boost pump might bump it up a little, but you have to be staring at it to notice.  As long as you are in the green it’s good.

[J0nathan225]

8 minutes ago, takair said:

Mine sits around 25 almost all the time.  Boost pump might bump it up a little, but you have to be staring at it to notice.  As long as you are in the green it’s good.

same 25-26 on the EDM 900. 23ish on the analog. 

[Hank]

18 minutes ago, J0nathan225 said:

same 25-26 on the EDM 900. 23ish on the analog. 

Ya'll and your high powered, fuel injected engines! Fuel pressure redline in my C is 6 psi . . . . Generally 2 or less in cruise, sometimes 1/2 psi.

[carusoam]

Green is good...

Outside the green is not always terrible, but can lead to other challenges down the line...

Best regards,

-a-

[outermarker]

Ok, I'll ask a dumb question. Can damage be caused if you forget to turn off the fuel pump and make a cross country (an hour or more) flight? How does the fuel servo handle the extra fuel  pressure over the engine driven pump pressure? You are still going to lean the mixture for whatever altitude you are cruising at so I would think the engine won't see a difference.

[RLCarter]

2 minutes ago, outermarker said:

Ok, I'll ask a dumb question. Can damage be caused if you forget to turn off the fuel pump and make a cross country (an hour or more) flight? How does the fuel servo handle the extra fuel  pressure over the engine driven pump pressure? You are still going to lean the mixture for whatever altitude you are cruising at so I would think the engine won't see a difference.

Extra fuel pressure not a big deal, electric fuel pump is not for continuous use, so may or may not make the trip

[Ragsf15e]

On 9/1/2020 at 8:18 PM, McMooney said:

Hello Mooneyspace,

 

my mechanics noticed the fuel pressure for my mooney rarely budges from approx 25psi; only changes when off or the electric fuel pump is on( 27 psi ).

is this the correct behavior?  I've always assumed it was normal.

 

Mine is exactly the same at 28psi.  I think you’re good.

[Ragsf15e]

8 hours ago, outermarker said:

Ok, I'll ask a dumb question. Can damage be caused if you forget to turn off the fuel pump and make a cross country (an hour or more) flight? How does the fuel servo handle the extra fuel  pressure over the engine driven pump pressure? You are still going to lean the mixture for whatever altitude you are cruising at so I would think the engine won't see a difference.

Probably not great for fuel pump, however, not gonna hurt the engine.

[McMooney]

8 hours ago, outermarker said:

Ok, I'll ask a dumb question. Can damage be caused if you forget to turn off the fuel pump and make a cross country (an hour or more) flight? How does the fuel servo handle the extra fuel  pressure over the engine driven pump pressure? You are still going to lean the mixture for whatever altitude you are cruising at so I would think the engine won't see a difference.

I have NEVER done this 

[carusoam]

1k’ agl...
 

Second check of...

1) Fuel pump off

2) Flaps up

3) gear up
 

Because every now and then... some distraction happens.

One of these things gets left in the wrong position...

One kills the pump....

the next causes cracks in the sub spar....

The third cause confusion when you put the gear up trying to land...

 

That first year can be tough on the Mooney... 
 

PP thoughts only, not a CFI...

Best regards,

-a-

[RobertGary1]

Mine used to vary a bit. Lycoming shipped my new engine with a new pump and now it’s always at the top of the green.  

 

-Robert

[J0nathan225]

On 9/10/2020 at 9:55 PM, carusoam said:

1k’ agl...
 

Second check of...

1) Fuel pump off

2) Flaps up

3) gear up
 

Because every now and then... some distraction happens.

One of these things gets left in the wrong position...

One kills the pump....

the next causes cracks in the sub spar....

The third cause confusion when you put the gear up trying to land...

 

That first year can be tough on the Mooney... 
 

PP thoughts only, not a CFI...

Best regards,

-a-

I forgot the pump once. I amended to doing a ~1k and double check once I level off for cruise like above.

[oldguyscanfly]

My 65 E is 26 psi fuel pump off, 27-28 fuel pump on.

Doesn't vary much.

[EricJ]

On 9/4/2020 at 10:03 AM, outermarker said:

Ok, I'll ask a dumb question. Can damage be caused if you forget to turn off the fuel pump and make a cross country (an hour or more) flight? How does the fuel servo handle the extra fuel  pressure over the engine driven pump pressure? You are still going to lean the mixture for whatever altitude you are cruising at so I would think the engine won't see a difference.

It depends on the pump.   I think most of the original pumps were not rated for continuous use, but iirc some of them are after overhaul.   You could find out what you have installed and the overhaul status, as it might make a difference.