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Mark Henderson

Well Known Member
Today was to be the first flight of N815W. As I taxied out to the runway the low fuel pressure alarm started going off. I had had an issue with this a few days ago, and thought it was resolved. I have verified that there is no blockage of any fuel line. The screen in the gascolator is clean. The fuel valve was fully open. Yesterday I had a consistent 3.3 psi of pressure. I parked the plane in the hanger for the night. I added 5 gal of fuel.

Today the pressure fluctuated between 1.5 and 2.7 PSI. Engine speed made no difference. The pressure would drop and the alarm would go off. After a few seconds the pressure would rise, then drop. In case it might be a blockage in the fuel vent, I had a friend pull the fuel cap off as I sat there. No change.
I taxied back to my hanger and pulled the top cowl. Nothing looked amiss. We disconnected the VA-216 fuel line from the sender and turned on the master. There was a good fuel flow, although I had no idea what the pressure was. After reconnecting the line I had 3.3 PSI with the engine running. After a short taxi it dropped to 2.7-2.8 PSI for no reason, then came back to 3.3 or so. There does not seem to be any rhyme or reason to the fluctuation. It was too late to find a mechanical fuel pressure gauge today. I have read other posts, and it sounds like it could be the Dynon sensor, or air in the line. I don't know why there would be air in the line after purging it 3 days ago.
Does anyone have any ideas?
 
PLACE A MECHANICAL GAUGE WHERE YOU CAN SEE IT

and check it against the sender. Senders are usually the problem . The mechanical gage can be temporarily plumbed to where you can visually see the pressure and can give you some indication where to go to next . Assuming you are set up with a carb mechanical and electric back up pump based on the pressures reported.
 
Mark Henderson said:
Today was to be the first flight of N815W. As I taxied out to the runway the low fuel pressure alarm started going off. I had had an issue with this a few days ago, and thought it was resolved. I have verified that there is no blockage of any fuel line. The screen in the gascolator is clean. The fuel valve was fully open. Yesterday I had a consistent 3.3 psi of pressure. I parked the plane in the hanger for the night. I added 5 gal of fuel.

Today the pressure fluctuated between 1.5 and 2.7 PSI. Engine speed made no difference. The pressure would drop and the alarm would go off. After a few seconds the pressure would rise, then drop. In case it might be a blockage in the fuel vent, I had a friend pull the fuel cap off as I sat there. No change.
I taxied back to my hanger and pulled the top cowl. Nothing looked amiss. We disconnected the VA-216 fuel line from the sender and turned on the master. There was a good fuel flow, although I had no idea what the pressure was. After reconnecting the line I had 3.3 PSI with the engine running. After a short taxi it dropped to 2.7-2.8 PSI for no reason, then came back to 3.3 or so. There does not seem to be any rhyme or reason to the fluctuation. It was too late to find a mechanical fuel pressure gauge today. I have read other posts, and it sounds like it could be the Dynon sensor, or air in the line. I don't know why there would be air in the line after purging it 3 days ago.
Does anyone have any ideas?
Click to expand...


Air in the line, not an issue.
Only one vent hole in the cap...more holes wont make any difference.
Problem with the electric fuel pump...possible but extremely unlikely,
Problem with the engine driven pump...also possible but also extremely unlikely.
It is most likely the sensor or the wiring connections related to it. Triple check the connections from the sensor to the D-180.
The sensors operating range is a rather low resistance so just a small amount of resistance from a poor connection can cause problems.

This type of sensor has a rather coarse resolution. Particularly when we are needing to read a rang of 3 - 4.5 PSI on a sensor with an operating range of 0 - 30 PSI (if I remember correctly). It wont really measure a change of 0.1 PSI. In fact, it wont necessarily indicate a change of 0.5 PSI, depending on where it is within its resistance range.

I'm sorry something as simple as this is holding up your first flight but working (as you are doing) to confirm the cause is the right thing to do.
 
Most senders do not have good resolution at low pressures, therefore there is some hysteresis in readings. 0.5psi is more than adequate, they will run with as little as 0.1psi. I wouldn't worry about 1.7psi.
 
Several -12 owners have reset the warning pressure to .05 PSI or lower so the warnings stop. I have yet to hear of any actual problems with the fuel pressure in the RV-12 set up.
 
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rvbuilder2002 said:
It is most likely the sensor or the wiring connections related to it. Triple check the connections from the sensor to the D-180.
The sensors operating range is a rather low resistance so just a small amount of resistance from a poor connection can cause problems.
Click to expand...

I haven't fired up my engine yet, but have seen a lot of posts regarding low and intermittent fuel pressure readings. If the sensing circuit is so sensitive to any resistance in the circuit, wouldn't it be a good idea to solder the female spade connectors to the ends of the brown wires at the sensor connection, rather than just crimping them?
 
BigJohn said:
I haven't fired up my engine yet, but have seen a lot of posts regarding low and intermittent fuel pressure readings. If the sensing circuit is so sensitive to any resistance in the circuit, wouldn't it be a good idea to solder the female spade connectors to the ends of the brown wires at the sensor connection, rather than just crimping them?
Click to expand...

John,

After your fly-off, go for it...not before.
 
I have had the same type of problems over the last year. Its always during the warm up and taxi out phase. Yesterday was a new one. I flew to another air port to sync the carbs on a Sport Cruiser for a fellow flyer. When I taxied out to leave the fuel pressure warning when off BUT this time it was HIGH pressure warning. First time that has happened . It cleared back to normal ranges in about 60 seconds .

Brad Stiefvater Salem SD 124Bj 140.5 hours now
 
mcems said:
I have had the same type of problems over the last year. Its always during the warm up and taxi out phase. Yesterday was a new one. I flew to another air port to sync the carbs on a Sport Cruiser for a fellow flyer. When I taxied out to leave the fuel pressure warning when off BUT this time it was HIGH pressure warning. First time that has happened . It cleared back to normal ranges in about 60 seconds .

Brad Stiefvater Salem SD 124Bj 140.5 hours now
Click to expand...

That has happened to me during taxi also. I turned ON the electric pump (I have it on a switch) and it went away. :cool:
 
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BigJohn said:
I haven't fired up my engine yet, but have seen a lot of posts regarding low and intermittent fuel pressure readings. If the sensing circuit is so sensitive to any resistance in the circuit, wouldn't it be a good idea to solder the female spade connectors to the ends of the brown wires at the sensor connection, rather than just crimping them?
Click to expand...

Hi John,
My understanding of aircraft wiring practices is that soldered connections make the wire brittle, while crimped connections made with the proper tools and connectors are designed to withstand vibration better and there should be no resistance due to a properly crimped connector. I think soldering is best for ham radio stuff ;).

Tony
 
I spoke with Dynon yesterday and they suggested that I make sure the sender was well grounded. The Adell clamp effectively issolates the sender from the aircraft. I put a ground strap on and was getting 3.6 psi with the engine running. I will see if this is a long term soloution.
 
Mark Henderson said:
I spoke with Dynon yesterday and they suggested that I make sure the sender was well grounded. The Adell clamp effectively issolates the sender from the aircraft. I put a ground strap on and was getting 3.6 psi with the engine running. I will see if this is a long term soloution.
Click to expand...

Mark, you got erroneous information from Dynon (I have already communicated with them about it).

Some of the sensors they supply for use with a D-180 do use the body of the sensor for the ground path.
The fuel pressure sensor used on the RV-12 has two wire connections. One is the sense line and the other is the ground, which is connected to one of the ground reference connections at the D-180. Generally, sensors that require a good airframe ground connection on the body only one wire connected to them. The sensor body ground replaces the second wire.

I still think you have a sensor problem. Have you double checked that the wire connections are good all the way back to the D-180, and have you checked the pressure with another gage for comparison? If you have, and you know for sure that the wiring is good, and that the fuel pressure is good and steady, and if Dynon wont offer another sensor to try, the best recommendation I can give is for you to lower your alarm threshold just enough to stop the low fuel pressure alarms.
 
Same low fuel pressure problem.

Sorry I copied this from my post under high fuel flow... I did get a high flow alarm at 7500ft but my real problem is low pressure... this sounds very much like Mark's problem.


I double checked the VA-216 line and confirmed the black fitting was connected to the fuel pressure sensor and the yellow fitting was connected to the return fuel line. I even pulled both fittings and did the blow test to see if the yellow side was more restrictive and it was. I checked the clamp block and made sure the jets were removed.. good too. The gascolator screen is clean and I'm getting a good flow from it all the way to the fuel pressure sensor.

Also I checked all the d-sub connections and they looked solid. I powered on the Dynon change the K value to 68000 (red cube). Without the engine running I'm seeing 2.2 gph flow and 0.2 psi of fuel pressure. I measured the voltage across the fuel pressure sensor and it was 202.3 mV. I assume that equals the 0.2 psi?

Bad fuel pressure sensor or fuel pump? With the engine running I'm getting around 3.0 psi. The first 3 hr. of running the engine I don’t recall seeing pressure problems. Only after 1.2 hr. of the first phase did this popup.

I did notice one thing when I pulled the line off the fuel pressure sensor… the fuel that leaked out was tinted orange-ish? More poured out the sensor when I shook it. Any ideas what that could be?

Thanks,
-Ron
 
We had erratic fuel pressure sensor readings on the RV-8 when it was first flying. Suspected poor electrical grounding of the sensor thru its threaded fitting screwed to the firewall-mounted manifold, so I added an extra ground wire attached to an ordinary stainless steel hose clamp (Breeze clamp) and tightened the clamp snugly around the body of the fuel pressure sensor, but not so tightly as to risk damaging the body of the sensor... just enough to ensure a good electrical connection. Fuel pressure readings have been rock solid ever since.

Even though the sensor's physical/mechanical mounting looked like it ought to be providing a solid electrical ground to the firewall, it actually wasn't.

Too bad they don't manufacture all types of these engine sensors with ground terminals deliberately made onto them.
 
I have a carb O-320 and my fuel pressure readings dropped off completely whilst I was flying (she was only at 8 hours TT). Anyway, she carried on flying fine and engine did not stutter.

When I eventually (I know, should really have fixed it when I landed) came round to fixing it, I bought a new sender, but that did not work. So I looked at the wiring (which should have been the first check) and found that the small resistor that the GRT EIS4000 has iin the feed to the transducer had loosened up. Quick turn of screw and all was good again.

No real loss as I need a transducer for the other PITA
 
Replaced the pump...

The electric fuel pump low pressure problem was the pump itself. I replaced it last night and now I have 2.2 psi without the engine running.

-Ron
 
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