High Fuel Pressure

[ALP]

I need some advice on fuel pressure on a 83 M20J. After a prop overhaul and some other work, my mechanic noted that the fuel pressure gauge was pegged on the high side. Fuel pump was removed and "black stuff" was noted so a new Lycoming pump was installed. No change. With a test gauge we found engine driven pump producing 29-30psi and the boost pump at 24ps which matches the panei. My panel guage is pegged in the red at 29. Pump specs call for 25-29 however, my A&P is unhappy with a redline gauge.

Has any body else had this issue and how was it resolved?

Al

[Marauder]

If I am not mistaken, fuel is pumped to the instrument to obtain the reading. Could it be the "black stuff" entered the gauge? Does the gauge go back to low pressure easily?

[ALP]

No, gauge moves freely and matches the shop's test gauge. To me, the black stuff appears like dirty fuel. More like a film (not gritty or chunky). I can't remember what the pressure was before doing the work - just that the needle stayed in the green.

The whole issue here boils down to 2-3# Pump specs are 25-29 and my gauge is in the red at 29. Pump people say pump is in spec. Servo people say they like 25-30+. Mechanic says no good because gauge says in the red zone.

[Marauder]

I searched the Mooney site and didn't see any service bulletins that pertained to the symptom you are seeing. Got me stumped. Hopefully others can chime in.

[ALP]

Thanks. I looked at a POH that I had downloaded and it states max fuel pressure at 30psi, Tomorrow I want to look at the POH  for the plane and see what that says. I don't know which would be the final rule poh vs gauge.

I haven't had this plane long and it is my first plane. I rented for many years, so this is a huge learning curve.

[Marauder]

The POH will be final rule. The gauge could have been changed out at some point with incorrect markings. Here is what mine looks like:

[Piloto]

It is likely a sender problem. When master is on and pump off does the gauge read some low pressure? If it does try cleaning the sender orifice with carburator cleaner. This is a common problem on the fuel and oil pressure gauges.

 

José

[Marauder]

It is likely a sender problem. When master is on and pump off does the gauge read some low pressure? If it does try cleaning the sender orifice with carburator cleaner. This is a common problem on the fuel and oil pressure gauges. José

The older Mooneys pump oil and fuel into the cabin to get the pressures. I have a nice braided oil line running up to my oil pressure gauge. The newer Mooneys may have transducers and sending units but I am not sure when the cut-over was.

[ALP]

POH says green arc is 14 to 30psi. Tested transducer with regulated air pressure and test gauge. When 30 psi was applied, unit would peg and stick and would not move until pressure was down to 25-26psi. When pressure was introduced slowly, gauge would rise smoothly matching test gauge. New transducer will be here on Monday.

Also, gauge has 30 written to the right side of the red arc. Our thought was that the red arc was less than 30 psi but the POH cleared that up.

Thanks for your help.

Al

[Rob 201MSE]

Having this issue since replacing my fuel pump as well.  I checked the Operators Manual for the Lycoming IO-360-A3B6 and it states the max fuel pressure is 35 PSI, so 30 to 31 PSI is well within specs.  The problem is Mooney's POH still has 30 PSI published a a pressure limit.  It would be nice if Mooney and Lycoming would come to some conclusion on this.

[EricJ]

3 hours ago, Rob 201MSE said:

Having this issue since replacing my fuel pump as well.  I checked the Operators Manual for the Lycoming IO-360-A3B6 and it states the max fuel pressure is 35 PSI, so 30 to 31 PSI is well within specs.  The problem is Mooney's POH still has 30 PSI published a a pressure limit.  It would be nice if Mooney and Lycoming would come to some conclusion on this.

The installation limitations override the engine limitations, so the POH limitations drive.   OTOH, the engine limitations tell you whether it'll cause an issue with the engine by itself or not.

 

[jetdriven]

On 5/31/2013 at 4:33 PM, Marauder said:

On 5/31/2013 at 2:54 PM, Piloto said:

It is likely a sender problem. When master is on and pump off does the gauge read some low pressure? If it does try cleaning the sender orifice with carburator cleaner. This is a common problem on the fuel and oil pressure gauges. José

The older Mooneys pump oil and fuel into the cabin to get the pressures. I have a nice braided oil line running up to my oil pressure gauge. The newer Mooneys may have transducers and sending units but I am not sure when the cut-over was.

1978. They took the fuel and oil lines out of the cockpit. Required AFM’s, shoulder harnesses. Airspeed in knots.  

[Pinecone]

The fuel pressure gauge in my plane (252) was max 30 psi.  It went well with the placard that stated that take off fuel pressure was 31 - 36.

Now replaced with Garmin EIS

[jetdriven]

I’ve been reading on here a lot of the mechanical fuel pumps from lycoming  in in the past few years are like a higher pressure pump and they picked out the gauge. Not gonna be done because you can’t buy one from them that is anything else.

The RSA fuel injector is kind of been sensitive to normal range fuel pressure. But continental different story. The fuel pressure kind of determines the fuel flow along with throttle lever position so when you talk about fuel pressure set up for metered and unmetered you’re looking at the metered.