fuel pressure

[721lp]

What fuel pressure do most of you see? .....1. When the electric fuel pump is on.....and 2. when only the mechanical fuel pump is on. 

[airfoill]

In typical cruise at 8000 without turbocharger, 20PSI.  With electric fuel pump on, 22PSI. 

Lower altitudes, like 3000, usually around 22 PSI.  Electric Fuel pump on, 24 PSI.

I have noticed that as I am climbing at high altitudes and full power, full rich with turbocharger on, it can go as low as 18PSI.  At cruise, it settles usually around 19 to 20 PSI with turbo.

Recently had an issue with the fuel pump fluctuating while at cruise which got my attention, but got it addressed.

[721lp]

Guys, let me be a little more specific....I have a '67 C model....so I don't have the higher pressure pump. I typically see about 5.5 psi in climb WITH electric pump on....the about 3 top 4 with it off......sound reasonable?

[mooniac]

721lp,

yep, those numbers match what I get in my 63' C model, same engine I assume O-360-A1D

[721lp]

Guys....one more question about fuel pressure. I typically see about 6 psi on take off with the electric pump on. When do most of you guys turn OFF the electric pump? If I turn mine off at about 2000 agl or so, the pressure can drop to as low as 2 psi....then it seems to come back up. I have replaced the mechanical pump about 2 weeks ago, because the pressure with it alone was going down to 0 sometimes, especially during climbout, but I could turn on the electric pump and the pressure would always come right back up. I guess the question I'm asking is; can the pressure vary that much between climbout and cruise? I also notice that turns , especially steep ones, can affect the pressure as well. The "green" arc is about 1 psi to about 6 psi, so I'm never out of that. I would also assume that during climbout you use much more fuel, hence maybe the lower pressure?

 

[Greg_D]

I had the same issue with a low fuel pressure reading on my M20F.  One day while in flight , I looked over and saw it reading zero.  That got my attention.

The problem was a clogged fitting on the back of the fuel pressure gauge.  The fitting is a sort of snubber valve that dampens out pressure pulsations from the fuel pump.  I took the fitting out and soaked it it carbueretor cleaner for a few hours.  That cleaned it out and life was good.

[721lp]

Greg,

That sounds entirely possible. I will check that next weekend .....annual time...

 

 

Jimmy

[721lp]

OK, guys....I need some guidance. My fuel pressure problem still rears it's ugly head from time to time. I have changed the mechanical fuel pump, found a pinhole in the fuel line coming from the carb. to the firewall, cleaned the snubber behind the gauge and it STILL sometimes goes to 0. It scares me some....but it always comes back up when I turn on the electric pump. I'm open to any suggestions.....

[eaglebkh]

Just curious - what is reading when the engine and boost pump are off?

I had to replace my MP/fuel pressure gauge recently because of a negative reading while off, and a very low reading while in operation. The if the negative value was added to the reading while operating, the resulting value was the normal value (20 psi).  A new gauge fixed all that.

[Amelia]

I'm fighting the same battle with my K-model. We've had the MP/FF gauge overhauled- found no problems, cleaned the electrical contacts and cleaned the transducer, which seems fine. Now trying to figure out if it's an electrical problem, seems that there's no power from the transducer to the gauge... finally got hungry and too dark to see, before we gave up for the night. Tomorrow's another day.   Annoying- and expensive. If anybody has some clever ideas, we'll be happy to hear 'em.

[triple8s]

I had fuel press readings that made me nervous, 1st thing I thought was replace the mech pump BTW its a "C" model. I didnt replace the mech pump instead I started with the cheap things. I cleaned the screen that's in the back of the carb and drained the carb bowl, that seemed to fix the problem for me. One thing that could definately cause low readings is a slight leak in the fuel line that is above the fuel level when aircraft is sitting, and is on the suction side of the mech pump. A leak on the suction side of the system will let air bubbles enter the fuel system and will cause a low pressure.

[Jim Peace]

On 10/27/2008 at 1:02 PM, 721lp said:

Guys, let me be a little more specific....I have a '67 C model....so I don't have the higher pressure pump. I typically see about 5.5 psi in climb WITH electric pump on....the about 3 top 4 with it off......sound reasonable?

that's about right......

[The Other Red Baron]

Over ten years old thread resurrected. That has to be some kind of record.

[Prior owner]

3 hours ago, revwatch said:

Over ten years old thread resurrected. That has to be some kind of record.

I can’t believe I missed that! I found it interesting though...

 

 

[Guest]

How long has Mooneyspace been going?

Clarence

[kortopates]

12 minutes ago, M20Doc said:

How long has Mooneyspace been going?

Clarence

Since the fall/winter of 2008 I believe - almost 11 years.

[kpaul]

17 minutes ago, kortopates said:

Since the fall/winter of 2008 I believe - almost 11 years.

I looked at Mooniac58's profile, October 11, 2008.

[Hank]

7 hours ago, kpaul said:

I looked at Mooniac58's profile, October 11, 2008.

I joined Oct 21, 2008.

My C often has ~2 psi in cruise. Whole different ballgame from my injected brethren. Oil lressure runs lower, too, I think. 

[DonMuncy]

6 hours ago, Hank said:

I joined Oct 21, 2008.

I got you beat by 3 days. October 18, 2008

[carusoam]

I was late to the party...

June 2009

I was looking for details regarding Missiles and found MS and some sparse info about Missiles...

MS had about 100 members before I joined...

Congrats to me! I’ve been here a decade, this Month...

in that time, I got an IR, bought an O, upgraded the power plant, got a class III SI, trained with some great CFIIs, met 100s of MSers...

Go MS!

Best regards,

-a-