New M20C owner w/ high fuel pressure

[George]

Hello to all..two weeks into aircraft ownership with 1964 M20C. Already on the board with my first question / problem. Fuel pressure is on the high side of green arc 6.5 - 7. Any thoughts on where I should begin with high fuel pressure? Previous topics w high pressure seem to be in the injected engines or did I miss HFP post  in carb engines?

Thanks,

G 

[Hank]

Welcome aboard, George! I really enjoy my C, and my wife likes going places in it. It's so, so, SO MUCH NICER than driving, and we won't even mention the incredible hassles of using the airlines . . .

My fuel pressure is generally 2.0-2.5 psi, but can pop as high as 5-5.5 or as low as 0.5 psi. It rarely stays at the outer limits for longer than a few seconds, but the engine hums along nicely the whole time, and airspeed and altitude are constant.

Does your fuel pressure stay high, or only rise occasionally? Does the engine run smoothly, make noises, speed change, etc.?

Other than this, hope it runs nicely and that you're having a good time with your new plane!

Edited November 2, 2016 by Hank

[DXB]

Congrats and welcome!

HIgh at all times or just at idle on the ground?   Mine definitely runs high on the ground - greater than 7- never gotten any A&P to take it seriously - the response of 2 MSCs has been "meh, that's what old Mooneys do."

[Raptor05121]

According to my checklist, fuel pressure should be between 4.0 and 6.0 on my bird. I'm trying to think of where I got that from. Either the operating limitations or the POH....

What year is your bird? (I'm also side interested because that tail number looks close to mine).

[Hank]

Here's the relevant page from my Owners Manual, which I can't highlight or otherwise mark up with my stinkin iPad. The checklist only mentions fuel pressure twice:  verify it's in the green arc, and verify that turning the electric fuel pump on makes it rise.

Which brings up another question--is your problem with the electric pump on or off? The values I quoted above are in flight, leaned,  electric pump off; don't think I've ever noticed it much on the ground, but I also lean about 2/3 or 3/4 to Cutoff on the ground.

[mike20papa]

Probably the old original gauge is more the problem than with a malfunctioning fuel pump, half the age.  Any difference between electric pump on/off, engine running or not?  I have an EI electronic fuel pressure gauge on my A model (same engine and systems as your C) and I get various pressure readings lot of times in the 6 plus, maybe 7 psi.  It's the couple of times it has blinked the red LED at me and I see the pressure around .5 that gets my attention.

[Guest]

If it's a concern, have a known good test gauge connected to the fuel pressure system and see what it says.  Rarely do fuel pumps fail to a higher reading.  More likely a faulty aircraft instrument.

Clarence

[Urs_Wildermuth]

I get this all the time when using the electric pump, but only then. The pressure goes way over red then, up to 6.5 or 7. Always been like this, even after the engine overhaul (with new pump) nothing changed. During flight it's normal.

[Piloto]

High pressure is not a problem at high power settings but at idle settings the carburetor float valve may not be able to close completely causing bowl overflow. It will cause a rough idle condition.

José

[DXB]

2 hours ago, M20Doc said:

If it's a concern, have a known good test gauge connected to the fuel pressure system and see what it says.  Rarely do fuel pumps fail to a higher reading.  More likely a faulty aircraft instrument.

Clarence

It was not a faulty gauge in my case - I changed from the factory gauge to an EDM900 in the first year of ownership, and fuel pressure on both gauges behaved precisely the same- high when on ground at idle, then pegged in the red when turning boost pump on before departure. It also runs high when turning on and reducing power before landing. The flashing red warning on the JPI is annoying, but I've been told so far that it's not a big deal. Worth investigating further?

[Andy95W]

7 hours ago, DXB said:

 Worth investigating further?

Probably not.  If you're concerned, reach in through the pilot's window and turn on your boost pump.  Let it run for a few minutes, checking for fuel dripping out of any of the overflow tubes on the bottom of the cowling, one just in front of the nose gear and one at the left cowl flap.

If you have any fuel leaking, your carb float seat valve will need attention, and your electric pump should probably be sent in for an adjustment.

But it probably won't leak fuel, because there really isn't much difference between 6 and 7 psi. 

[DXB]

39 minutes ago, N1395W said:

Probably not.  If you're concerned, reach in through the pilot's window and turn on your boost pump.  Let it run for a few minutes, checking for fuel dripping out of any of the overflow tubes on the bottom of the cowling, one just in front of the nose gear and one at the left cowl flap.

If you have any fuel leaking, you're carb float seat valve will need attention, and your electric pump should probably be sent in for an adjustment.

But it probably won't leak fuel, because there really isn't much difference between 6 and 7 psi. 

Yeah makes great sense - will give  a try at some point.   As you note, the normal fuel pressures are really quite low in the carb'd systems relative to the fuel injected planes, and I wonder if the two fuel pumps are even capable of generating pressures that threaten the structural integrity of the system.  I also wonder how the 7psi upper limit set in the TCDS in the early 60s was derived - it may be pretty meaningless.  The flashing red warning on the JPI before every takeoff and landing is a distraction though when I have other things on my mind.

[George]

Thank you all...The fuel pressure is high on ground at idle (1000rpms) without boost pump. Taxied aircraft today and FP was at 6psi a little lower as I increased power for taxi.

Hank- engine runs smooth for most part (another potential post if new plugs all around do not cure the occasional knock / miss?? not sure how to describe it) during descent & power reduction. Ran just fine at altitude 7500ft on flight back from TX. FP was 4-5 psi at altitude.

DXB- yes on the ground. seems to remain in the green at higher power setting.

Raptor - 1964 N7164U

Will try the suggestions and see what I find out this weekend.

 

Thanks,

George (AKA Hank but that name was already taken LOL!!)

[Andy95W]

5 minutes ago, George said:

 engine runs smooth for most part (another potential post if new plugs all around do not cure the occasional knock / miss?? not sure how to describe it) during descent & power reduction. 

It sounds like you need to lean your mixture more.  Our carbureted O-360s are set up really rich when they're not at full power.  On the ground, you can't hurt your engine by leaning it so it barely keeps running, and you'll likely never again have a fouled plug.

In flight, during a power reduction and descent, you should also be leaning from where you were cruising.  There are posts here about "Target EGT" that Hank has contributed to in the past.  Worth reading.

Regardless, you definitely can't fly the M20C the way most flight instructors taught us to fly C-172s.

[Urs_Wildermuth]

Oh yes, on ground leaning is absolutely a must in the C. Also agressive leaning in any phase of flight is quite necessary to keep fuel flow and performance going. Much different from certain Cessnas where the effect of leaning is hardly noticable.

[Hank]

51 minutes ago, George said:

Thank you all...The fuel pressure is high on ground at idle (1000rpms) without boost pump. Taxied aircraft today and FP was at 6psi a little lower as I increased power for taxi.

Hank- engine runs smooth for most part (another potential post if new plugs all around do not cure the occasional knock / miss?? not sure how to describe it) during descent & power reduction. 

George (AKA Hank but that name was already taken LOL!!)

On the ground, I lean enough that advancing the throttle for uphill taxi makes her stumble unless I also push mixture forward. My plugs are almost never fouled, unless I forget to lean after landing . . .

I'm not sure what you mean by combining "power reduction" with "descent." I push the yoke for 500 fpm and trim the force away. As I come down, I periodically reduce MP to wherever it was set during cruise, then push in mixture to regain cruise EGT. My power reduction comes just before pattern entry, not before, unless I'm shooting an approach--then I pull it far enough before the IAF that I can get slow somewhere near it.

          --Hank (but I'm really George)  

Edited November 2, 2016 by Hank

[DXB]

When I got my plane, no one taught me that I need to lean aggressively at all times when on the ground.  But then my plane schooled me on this very quickly!

[George]

Will try some aggressive leaning! Flew with my son last night while he worked on night landings...fuel pressure hung around 5.5 without boost. Will keep an eye on it. 

The occasional knock/miss/stumble had me thinking if I had leaned to aggressive or I had not advanced mixture enough for the descent. Noticed a few times last night in the pattern with no leaning...will lean next time see if that helps... A&P is going to ride with me next flight..

Its been 21 years since I've flown recips... This will be a learning process not only for my boys building time but for me as well! And I do enjoy the lower altitude flying!

GHW

[Andy95W]

Here are a couple of articles for you to ponder:

https://www.jpinstruments.com/wp-content/uploads/2013/05/Mike-Bush-Red-BoxRed-Fin.pdf

http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning-198162-1.html

Basically, below about 19" MP, you can lean all you want any never hurt your engine (just make sure you enrichen before adding power for a go-around).

It sounds like you fly for a living.  There are a few of us here who do that.  Welcome.

Let us know how it goes.

[George]

Great articles....I am now going to spend a little time learning the Insight 602 GEM installed in the plane!

GHW