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  #1  
Old 06-27-2017, 01:18 PM
mwardle7 mwardle7 is offline
 
Join Date: Oct 2009
Location: Utah
Posts: 34
Default Rotax High Fuel Pressure

I'm am perplexed with a high fuel pressure issue.

My Rotax 912 ULS was shipped to me in March 2016. First flight was in January 2017. I'm using the G3X system. I have 50 hours on the airplane.

On my last flight I had unusually high fuel pressure readings. It came on suddenly and hasn't gone away. I can't tell if I have a bad fuel pump, an electrical problem, a plugged carb/gascolator, or something else.

Below is graph showing the fuel flow and fuel pressure over the 1.5 hr flight from Vernal, Utah to Salt Lake City. Given the constant fuel pressure warnings, I pulled the fuel pump fuse once I had reached altitude. You'll note that fuel pressure stabilized within the "green" when the fuel pump fuse was pulled, but it was still erratic. What is really perplexing is the decrease in fuel flow once the pressure increased at the end of the flight.



Any ideas on where to start?

Thanks much!
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  #2  
Old 06-27-2017, 09:12 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
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Might be a bad fuel pressure sensor.
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  #3  
Old 06-27-2017, 10:04 PM
John-G John-G is offline
 
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Location: Northeast Ohio
Posts: 427
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If it turns out that the high fuel pressure is actually correct (verified with a gauge) then the next item you may want to have a look at would be verifying the tiny orifice in the fuel return line is not blocked or partially blocked.

I think it is quite likely one would see higher than normal fuel pressure readings if that small orifice in the fuel return line were to become blocked.
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  #4  
Old 06-27-2017, 10:32 PM
mwardle7 mwardle7 is offline
 
Join Date: Oct 2009
Location: Utah
Posts: 34
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Quote:
Originally Posted by John-G View Post
If it turns out that the high fuel pressure is actually correct (verified with a gauge) then the next item you may want to have a look at would be verifying the tiny orifice in the fuel return line is not blocked or partially blocked.

I think it is quite likely one would see higher than normal fuel pressure readings if that small orifice in the fuel return line were to become blocked.
Thank you. I'll be checking the fuel pressue with an independent gauge tomorrow. Where is the orifice in the return line?

I noticed this evening that with the engine off and the aux fuel pump off the fuel pressure reads 3 psi. Wierd.
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  #5  
Old 06-27-2017, 11:25 PM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
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Quote:
Originally Posted by mwardle7 View Post
Where is the orifice in the return line?
It is inside the VA-216 hose unless you have a modified fuel system. Have a look at page 46-11 in the plans.

Also have a look at page 46-09 and verify that the pilot jet was removed from the banjo fitting mentioned in step 9.
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  #6  
Old 06-28-2017, 05:39 AM
BigJohn BigJohn is offline
 
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Location: Gloversville, NY
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Quote:
Originally Posted by mwardle7 View Post
..........I noticed this evening that with the engine off and the aux fuel pump off the fuel pressure reads 3 psi. .........
So right away you know there is something wrong with the information you are getting. Fix that first since it is the most obvious anomaly.
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  #7  
Old 06-28-2017, 08:37 AM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 584
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Quote: "I noticed this evening that with the engine off and the aux fuel pump off the fuel pressure reads 3 psi. Wierd."


I know of many (including mine) RV-12s with Dynon SVs that display a couple of PSI when the engine and electric fuel pumps are OFF. I have heard that it is just an instrumentation characteristic of the SV /sensor installation.
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Last edited by DHeal : 06-28-2017 at 08:43 AM.
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  #8  
Old 06-28-2017, 04:52 PM
mwardle7 mwardle7 is offline
 
Join Date: Oct 2009
Location: Utah
Posts: 34
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It looks like I have a bad fuel pressure sending unit.

I added a mechanical fuel pressure gauge to the system. There is a handy 1/8 FNPT fitting on the top of the engine where the fuel lines come together. You can tap it to it by removing the hex plug. I added the gauge ($20 from my local auto parts store) and compared with what I was getting on the G3X. With the aux pump off and the engine off, the mechanical gauge showed 0 and the G3X fuel pressure showed 3.3 PSI. With the aux fuel pump on, the mechanical gauge showed 4 PSI and the G3X showed 6.3 PSI. I didn't start the engine to see what it would read with both pumps working.

I also used a multimeter to test the sensor for ground continuity (good) and 5 volts on the power wire (good).

I also tried picking all of the different sensors listed in the Engine configuration page of the G3X. That wasn't helpful. The readings were all over the place.

Next step: new fuel pressure sending unit.

Hopefully my troubleshooting steps will be of benefit to others at some point.
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  #9  
Old 08-02-2017, 02:26 PM
AirHound AirHound is offline
 
Join Date: Oct 2006
Location: OFallon IL now, everywhere before
Posts: 132
Default RV-12 Electric Fuel Pump (electronical filter)

Do all kits EAB and ELSA call for an electric filter wired into the fuel pump circuit/at the electric pump? Are they for RFI reduction? As in negating the FP noise over the headphones? Do SLSA models have them? Thank You!

Quote:
Originally Posted by mwardle7 View Post
It looks like I have a bad fuel pressure sending unit.

I added a mechanical fuel pressure gauge to the system. There is a handy 1/8 FNPT fitting on the top of the engine where the fuel lines come together. You can tap it to it by removing the hex plug. I added the gauge ($20 from my local auto parts store) and compared with what I was getting on the G3X. With the aux pump off and the engine off, the mechanical gauge showed 0 and the G3X fuel pressure showed 3.3 PSI. With the aux fuel pump on, the mechanical gauge showed 4 PSI and the G3X showed 6.3 PSI. I didn't start the engine to see what it would read with both pumps working.

I also used a multimeter to test the sensor for ground continuity (good) and 5 volts on the power wire (good).

I also tried picking all of the different sensors listed in the Engine configuration page of the G3X. That wasn't helpful. The readings were all over the place.

Next step: new fuel pressure sending unit.

Hopefully my troubleshooting steps will be of benefit to others at some point.
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