M20C Fuel Pump

[captainglen]

The engine overhaul manual for the O-360-A1A manual specifies a low pressure pump with a 4 PSI to 6 PSI output. The Facet boost pump puts out 25 PSI. The fuel pressure gauge green arc is marked from 14 PSI to 30 PSI. Is anyone knowledgeable on this subject. I could find no service bulletin or AD that affected the output of the engine pump only the replacement of single diaphragm pumps with double diaphragm pumps. If the 4-6 PSI is correct then the pressures I observe in cruise flight are normal and the instrument markings are for boos pump operation only. HELP!

[Hank]

My C generally cruises around 3 psi fuel pressure. Memory says the green arc is 0.5-6, with a wider arc from 2.5/3 up to 5.5/6.

The 25-30 psi sounds like that for the fuel-injected models E, F, J.

I'll have to look for a picture, none here on my iThingy . . . Except one shot from the left where the Fuel Pressure needle is visible but not the numbers.

[mooniac15u]

Hank's numbers sound about right. The POH would be a good place to look for the normal range. 

[mooniac15u]

Sounds like you have this gauge which is for a FI Mooney:

 

Rather than this gauge which is what you should have for an M20C:

[Hank]

Mine is the lower one but turned around. 

[captainglen]

  Mooniac you are right that is the gauge I have. Hank your gauge illustrates two problems, wrong gauge and wrong boos pump since the pressure goes up to 22 when the switch is on. I have observed that if I switch the boost pump on too soon before starting and do not shut it off that I vent some fuel onto the ground.

  Not only will I check the POH but the part numbers in the original type certificate and the standard instrument marking section of the manufacturer equipment list (I have a copy from FAA records. Thank you all so much!

[Hank]

Glen, the numbers are the same on my gauge and Craig's, both peak at 10 psi. The second needle on both is Manifold Pressure, using the scale from 10-30 and the needle marked "M"; the needle marked "F" is fuel Pressure, and uses the scale from 0-10.

If your C ever really puts out 22 psi fuel pressure (and not just because you have the wrong numbers painted on), then you have a serious problem . . .

[DrBill]

Glen, Looks like you have an electric pump for an injected engine. Probably the wrong P/N..

My "E" has pressure c25 on prime and then mechanical should be 15-25 but currently running 50 so I'm replacing the mechanical.. Electric is OK at 25.

Bill

 

[mooniac15u]

When you fly this plane what pressure do you see from the mechanical pump?  I can't imagine it's anywhere near the green arc on the gauge. 

[mooniac15u]

3 hours ago, captainglen said:

  Mooniac you are right that is the gauge I have. Hank your gauge illustrates two problems, wrong gauge and wrong boos pump since the pressure goes up to 22 when the switch is on. I have observed that if I switch the boost pump on too soon before starting and do not shut it off that I vent some fuel onto the ground.

  Not only will I check the POH but the part numbers in the original type certificate and the standard instrument marking section of the manufacturer equipment list (I have a copy from FAA records. Thank you all so much!

I assume you mean the parts catalog rather than the type certificate. It don't recall seeing part numbers for gauges in the type certificate. 

[Guest]

I agree with Hank, your airplane seems to have some incorrect parts.  Your fuel pressure is way too high, under 6 with the engine running and the fuel boost pump on.

Clarence

[DXB]

20 hours ago, captainglen said:

The engine overhaul manual for the O-360-A1A manual specifies a low pressure pump with a 4 PSI to 6 PSI output. The Facet boost pump puts out 25 PSI. The fuel pressure gauge green arc is marked from 14 PSI to 30 PSI. Is anyone knowledgeable on this subject. I could find no service bulletin or AD that affected the output of the engine pump only the replacement of single diaphragm pumps with double diaphragm pumps. If the 4-6 PSI is correct then the pressures I observe in cruise flight are normal and the instrument markings are for boos pump operation only. HELP!

You have the wrong gauge as others note.  BTW PM me in case you need the correct MP/FP gauge- I have one removed from my '68 C last year when I added a JPI as primary.  

[captainglen]

Once again this community has been invaluable to me! I now have the correct boost pump installed and the correct fuel pressure gauge and can now move on to cosmetics and make the airplane look pretty. THANK YOU ALL.

 

[carusoam]

Go MS!

-a-