Fuel pressure question for carbureted engines.

[AX-O]

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.

[Walt]

5 psi nominal, 4-6 psi range is "normal".

[David Z]

I don't have the book here, but 8psi is what comes to mind for the maximum.

[Neal@F14]

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

[AX-O]

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.

[Neal@F14]

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.

[apkp777]

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.

[Camillo]

From a different thread (and from my POH):

Fuel pressure

Over 8 PSI red
0,5-8 green
under 0,5 red

[scard]

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?

[Ken]

A J3 Cub has gravity feed.

Ken