AX-O

AX-O

Well Known Member
The EFIS on my flying RV has all the limits (temp, pressure, etc.) set-up by the previous owner. The fuel pressure is constantly running in the yellow arc with the electric fuel pump turned off and on. I don?t think that the yellow arc is correct. What is the ?normal? or ?average? fuel pressure I should see when the electric fuel pump is off and on? Thanks for any help or guidance you can provide.
 
On my carbureted Cherokee, the factory FAA approved green arc on the fuel pressure gauge is between 0.5 and 6 PSI. I normally see about 5psi at all times with the boost pump either on or off, it only rises slightly with the electric boost pump switched on.

I'd reckon that on a carbureted RV the limits would be very similar. Probably something like:

Lower red/yellow limit 1 psi
Lower yellow/green at 2 psi
Upper green/yellow at 6 or 7 psi
Upper yellow/red at 8 psi
 
Sometimes I see just over 12 PSI. I wonder if there is something wrong with the sensor (it was replaced in 2009). Or if the reading is correct. I have not experience any problems so far.
 
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I'll bet you have a poor electrical ground on the fuel pressure sensor. The higher the resistance in the ground circuit of the sensor, the higher the pressure reading will erroneously show.

The sensor is a variable resistor inside, and when the hot wire is grounded, will show 0 psi, the higher the ohms thru the whole circuit, the higher the PSI reading will be. Thus if the ground connection of the sensor is not solid, it will add ohms to the total circuit and your reading will be high PSI.

I ran into exactly this same problem on the RV-8 (fuel injected) and saw reading spiking as high as 50 psi !!! I added a new ground wire attached to a stainless steel "breeze clamp" tightened snugly around the sensor, but not so tight as to risk crushing or deforming the sensor, and the erroneous high fuel pressure readings vanished.

I wished these fuel pressure sensors had a separate dedicated ground connector on them, would help eliminate this problem. You cannot trust just having the sensor screwed into a manifold bolted to the firewall to provide a rock-solid electrical ground.
 
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Check your sensor input mapping. I know that on the Dynon there are 2 options for fuel pressure sensors. It's possible that the wrong one is selected.
 
From a different thread (and from my POH):

Fuel pressure

Over 8 PSI red
0,5-8 green
under 0,5 red
 
Heck, we see negative numbers for fuel pressure often enough (standard Vans O-320 setup w/ GRT eis). The engine keeps running fine. I've learned not to be concerned with that one. Does a J3 Cub have a fuel pressure guage?
 
IIRC, the TCDS for the O-320 lists 0.5 PSI as minimum required fuel pressure. My experience with most electronic fuel transducers are that they have a hard time reading that low. Most read from 0-60 psi and the low end of 1/2 psi is sometimes reading zero on the meter.

On my airplane, I typically see 1 PSI but also sometimes see ZERO. I have turned the alarm function off on fuel pressure. I rely more on fuel flow than pressure with my carb equipped 320.
 
RV6_flyer said:
On my airplane, I typically see 1 PSI but also sometimes see ZERO. I have turned the alarm function off on fuel pressure. I rely more on fuel flow than pressure with my carb equipped 320.
Click to expand...

Same on my O-360 carbed engine. I biased my fuel reading by +1 PSI to eliminate the alarms.
 
Low Fuel Pressure

RV6_flyer said:
IIRC, the TCDS for the O-320 lists 0.5 PSI as minimum required fuel pressure. My experience with most electronic fuel transducers are that they have a hard time reading that low. Most read from 0-60 psi and the low end of 1/2 psi is sometimes reading zero on the meter.

On my airplane, I typically see 1 PSI but also sometimes see ZERO. I have turned the alarm function off on fuel pressure. I rely more on fuel flow than pressure with my carb equipped 320.
Click to expand...

OK Gary and Ron...Today I started my RV-6 0-360 carbureted Lycoming for the first time. I have Van's fuel pressure gauge and transducer. It read approx. 2#'s and didn't change with or without the aux fuel pump. I did a fuel flow test and got to the gallon fill mark in about 2 1/2 minutes. Looks like fuel flow is great but pressure is either low (don't think so) or the gauge or transducer isn't working (kind of like my Van's fuel gauges)

Do I rely on the fuel flow test and am I good to go with lousy readings on the gauge.
 
Gary, that equates to 24 gallons per hour. I hesitate to suggest what is adequate but my plane works fine with a reading of well below yours.

The 7A I am flying runs 3.5ish to 4.5ish PSI. Does not seem to change with electric boost pump on.
 
Thanks for the info

Ron Lee said:
Gary, that equates to 24 gallons per hour. I hesitate to suggest what is adequate but my plane works fine with a reading of well below yours.

The 7A I am flying runs 3.5ish to 4.5ish PSI. Does not seem to change with electric boost pump on.
Click to expand...

Thanks Ron. Glad to know that it doesn't seem to be a problem.
 
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