Low Fuel Pressure

[Dave Holl]

Should a non return valve be fitted in tis line at the firewall?
Dave

[Dave S]

Dave H

In my opinion, a person should follow the recommendations of Rotax for the specific engine regarding how to hook this up. If you happen to have the engine installation manual; or search their site - you should be able out find what their recommendation is.

Sincerely,

DS

[kitfox2009]

Hello All
Yesterday I installed my new fuel return line. I obtained the "pilot jet" from Rotax. This is a threaded jet designed to fit in the Rotax fuel distribution block. Probably a similar unit could be obtained from a motorcycle shop. Anyway, with a slight modification I installed it in the fitting going into the top of the gascolator. The fuel pressure stays at 5 PSI through all power settings and drops to zero within seconds after shutdown. I have not had the opportunity to test it for hot starts yet but hopefully this will eliminate the problem.
Cheers
Don

[Dave S]

Don,

Thanks so much for posting your results so far. Will certainly be interested in how the hot starts work out. Sounds like your fuel pressure is right where it should be now.

Do you happen to have any photos you could post which show the completed installation layout including the gascolator hookup?

I have been mulling this over in my mind for a while but haven't taken the step to do it yet - but do want to to. I have the occasional hot start deal going on too; and, I don't have a gascolator (another likely improvement).

Sincerely,

Dave S

[cardinal flier]

After three low pressure warnings, on three different flights, and in totally different flight conditions, and a LOT of attempted fixes to the fuel system, I think I finally found the reason I got a "low fuel pressure" warning on my Dynon. I installed a mechanical guage to test the accuraracy of the Dynon system and got approximately .5lb. lower readings with the Dynon, and variations of the spread between the Dynon and the mechanical. So, yesterday I asked Dynon if they had any history of problems with the fuel pressure sender. Dynon stated that they no longer sell the unit I had because of all the problems with the unit. The unit was prone to reading low at lower pressure from the pump. (Yes John, I can hear you all the way from Idaho, laughing, and saying "I told you so") I tested the mechanical and the Dynon guage today and the Dynon reads lower than it should. So, I've got the new, latest design, unit on order from Dynon and am hopeful of the solution. I'm also going to install a 1" fuel pressure guage in the panel as a back up to the Dynon.
Bruce Estes

[kitfox2009]

Hello All
I know this is an old thread but I would like to reactivate it. I was overseas for 4 months so I drained all the fuel from the Vixen and parked it in the garage. On startup last week all was normal on taxi and runup but about 2 or 3 minutes into climb out the fuel pressure started dropping (normal is 5 psi)and fluxuating in the 1 to 2 psi range. Throttle back on downwind with full 5 psi.
Suspecting a weak pump or restriction I did a fuel flow test today and get 20 lites in 12 minutes or 100 lites an hour. Lots of fuel!
The engine is mid 90`s 912UL with 400 hours and the original fuel pump. I also installed a return line back to the gascolator last year.
Is this the type of behavior that a worn pump would exibit? At rpms up to 4000 or so the fuel pressure remains at 5psi. at closer to 5000rpm the pressure gradually reduces.
Anyone have this experience or should I just go buy a new pump. It is probably due anyway.
Your comments/experience appreciated
Don

[kitfox2009]

Also different topic but my Westac Quad gauge oil pressure jumps up to 100psi (at times, sometimes even after shut down). I suspect the sending unit but Westac has now changed to a different style.
Would anyone have a spare 378-MM sender in their parts tray. Preferably new or with very little use.
If necessary I may have bite the bullet and upgrade to more modern stuff. Suggestions????
Cheers
Don

[Dave S]

Hi Don,

I'll take a stab at your question; but, since I am not on site with you looking at the issue first hand, I could easily overlook something so take that grain of salt with my comments.

First off, the scenario you describe, the fuel pressure dropping with higher power output when it is apprent the system has adequate flow generally is what you see with a weak fuel pump. Your analysis is spot on. Anybody's guess if the cause was the due to the draining of the system; however, fuel pump poppet valves can stick, diaphrams can break down with drying out.

Second, gauges sometimes lie.....it is entirely possible for an electronic gauge system to display low fuel pressure even if the pressure is OK. The way this is normally sorted out is to plug in a direct reading gauge; or, a known good pressure monitor to see if the gauge displaying the low reading is lying or not. Easy to do on the ground.....not so easy to do in flight without a lot of messing around .

Another consideration. If the fuel pump is original and goes back to the 90's, I think Rotax has aa recommended replacement schedule for the fuel pump at a much shorter interval.

On your other gauge deal, I am not so sure; but, these types of anomalies can certainly be caused by less than perfect electrical connections or the gauge in addittion to the sensor....sorting that out is good to do. If you are lucky enough to have the original documentation for the quad gauge, I believe they include a basic troubleshooting guide.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp
St Paul, MN

[thilokind]

Hello everyone,

I seem to have the exact same problem than Kitfox 2009:

after a few minutes in flight the fuel pressure is slowly decreasing. Normally, I see 5 to 6 psi, but it slowly keeps dropping to 20 psi. The engine never misses a beat, even at WOT. When coming in for landing and reducing throttle, the fuel pressure climbs up to 5 to 6 psi.
My setup: two leading edge wing tanks, each with the own electrical fuel pump, connected in series with the engine driven fuel pump.
Switching the electrical fuel pumps on or off does not change anything.
So far I have:
- replaced all fuel hoses in the engine compartment
- replaced one of the electrical fuel pumps
- temporarily re-installed an old Pierburg mechanical fuel pump
- replaced the fuel pressure sensor
- cleaned the fuel filters multiple times
- checked the fuel flow with the electrical pumps on - there is plenty of fuel flowing to the carburetors.

Anybody with an idea:
@ Kitfox 2009: did you ever found the reason for this behavior? How did you fix it?

Thanks a lot

[kitfox2009]

Hi Guys
Back in 2013 at 401 hours I replaced the original fuel pump with the updated one with the "over flow/pressure" nipple that must be directed overboard.
No issues since. Now have 750 hours. Runs 4 or 5 pounds steady.
Seems like it`s just like being in the oilfield. Keep throwing money at it until it works!!!
Have fun Don