Greg Arehart

Greg Arehart

Well Known Member
No luck finding anything in the archives. I'm wondering what kind of variation folks out there are seeing in fuel pressures with the engine pump only. I am running a Superior IO-360 and my fuel pressures are generally between about 23 psi and maybe 28. Some days I see fairly constant fuel pressure, whereas other days the pressure seems to fluctuate a lot and may spike as high as 32-34 psi. All this is within limits, but the variation seems odd to me. I have not put a restrictor in the line as is commonly done for manifold pressure. I also realize that there will be some variation related to RPM, but the variation I am seeing is at much higher frequency than any RPM changes. Is this variability normal or something to worry about?

Thanks for any insights.

greg
 
Fuel Pressure Indications

Greg Arehart said:
No luck finding anything in the archives. I'm wondering what kind of variation folks out there are seeing in fuel pressures with the engine pump only. I am running a Superior IO-360 and my fuel pressures are generally between about 23 psi and maybe 28. Some days I see fairly constant fuel pressure, whereas other days the pressure seems to fluctuate a lot and may spike as high as 32-34 psi. All this is within limits, but the variation seems odd to me. I have not put a restrictor in the line as is commonly done for manifold pressure. I also realize that there will be some variation related to RPM, but the variation I am seeing is at much higher frequency than any RPM changes. Is this variability normal or something to worry about?

Thanks for any insights.

greg
Click to expand...

Greg:

I have no Idea of which EFIS/Pannel Indicator you have. I have a Grand Rapids EFIS and had their German "VDO" Fuel Pressure Indicator which wasn't up to the standards that I thought it should be. I kept getting alarms that never happened with the old Dynon and earlier Van's steam guages. I switched to their upgraded sensor. ($130.00+) which works great. PM me for my phone # if you need more info.
 
Mannan,

I am using the Dynon D120, if that helps....sounds like you did not have such problems with the Dynon.

greg
 
I am running a Superior IO-360 and my fuel pressures are generally between about 23 psi and maybe 28. Some days I see fairly constant fuel pressure, whereas other days the pressure seems to fluctuate a lot and may spike as high as 32-34 psi.
Click to expand...
We have the same... Done nearly 150hrs and it is the same as it was at the start, and still haven't got around to doing anything about it :confused:

Either a dodgy/unsuitable sensor (Dynon D-180), or the long pipe up to the Sensor has air in it (hard to drain), and some harmonic sets up in there. The moment you put the electric pump on it settles down with no change in engine behaviour... I think I have heard someone else with the same setup with the same "issue".

We also changed the Mech Fuel Pump at about 30hrs (unrelated reason) and same behaviour before and after.

Andy & Ellie Hill
RV-8 G-HILZ
 
I have little to no variation

I am using the Van's steam gage and get very little difference in fuel pressure flight to flight. I do get a rise in fuel pressure of maybe 5 psi when i have the the electric fuel pump on.

One other varible besides the gage and sensor is the location of where you are taking the pressure reading. I wondered where the best place to read the pressure should be. I opted for the port on the side of the servo (I have the Bendix RSA-5AD1) where the the intake screen is. I thought I wanted to know the pressure coming into the servo but just after the screen. I figure it would tell be something if the screen got clogged. I know some have the pressure sensor in the line after the engine driven pump before the servo and others use the pressure up on the spider.
 
I don't think it is the pump. More than likely it is the transducer and/or indication circuit.

I am running with EIS 4000 and the mechanical pump pressure is rock solid at 21 psi and the electric pump at 29 psi. Neither varies but 1 or 2 psi.
 
After looking through a bunch of my Dynon D120 data, I thought I would revisit this issue. My sampling interval is 3 seconds, for the record. Whenever the boost pump is on, the pressures are absolutely constant - essentially zero fluctuation at about 31 psi. This leads me to believe that the problem is NOT in the electronics. Without the boost pump (mechanical pump only), pressures are erratic at best (22+/- 2 psi and spiky, not smooth fluctuations) and can spike as high as 40 psi. Sometimes, the pressures stay within the +/- 2 psi for tens of minutes (still far jumpier than with the boost pump on), then apparently randomly begin spiking quite high. Changing the throttle (i.e., RPM) does not fix the problem, so I don't believe that it is related to a harmonic in the pump or line. My fuel pressure takeoff is a T just downstream of the mechanical fuel pump. I also have put a restrictor (rivet with tiny hole) in the fuel pressure line near the FP gauge. My ideas on what might be causing this fluctuation are:

1) check valves in the pump are occasionally sticky?
2) something to do with the fuel flowing in an odd pattern near the FP takeoff line (in the T)?
3) clogged breather line?
4) some sort of sporadic leak across the pump diaphragm?

I'm grasping at straws. Any other ideas out there? Am I missing something obvious? Any thoughts on diagnosing the problem?

thanks,
greg
 
Could be the pump but before that, I would try bleeding all the fuel out of the sensor line until it is empty and then hook it back up. Maybe it is a sampling or gauge sensitivity issue that the air cushion, in the line, might dampen.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
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