English French German Italian Portuguese Spanish Swedish

 

Intermittent Low Fuel Pressure

  • Solarguy54
  • Solarguy54's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
5 months 6 days ago #18791 by Solarguy54
Intermittent Low Fuel Pressure was created by Solarguy54
2012 CTLS, just did 5-year rubber replacement. In warm weather and after long taxi at low power, when full power is added (takeoff WOT), fuel pressure will drop generating a warning light. In addition, at the same time, fuel flow briefly climbs to 10-11 gph, then fuel pressure rises to normal and fuel flow drops to normal full power climb rates. Have changed fuel pump (twice). Thoughts? Thanks!

Please Log in or Create an account to join the conversation.

More
5 months 6 days ago #18792 by garrett
Replied by garrett on topic Intermittent Low Fuel Pressure
I have a 2009 Remos GX and have similar issues. My fuel pressure drops after leveling off or during a decent and leveling back out. The problem has not been as bad with the new style pump, but no one seems to be able to explain this.

Please Log in or Create an account to join the conversation.

More
5 months 4 days ago #18826 by jiott
Replied by jiott on topic Intermittent Low Fuel Pressure
I have had the same issue for 600 hours. The engine has never hiccuped once when the fuel pressure was in the warning area at WOT, so I quit worrying about it. Sure wish someone could explain it though. I know there are several others who have this same issue in varying degrees. Supposedly the Rotax factory was looking into this several years ago, but nothing has ever been said about it.

Please Log in or Create an account to join the conversation.

More
5 months 1 day ago #18901 by bstrachan
Replied by bstrachan on topic Intermittent Low Fuel Pressure
I had intermittent low fuel pressure warnings ( < 2 PSI) for years. StingSport low wing, fuel tank under the cockpit floor. Never had the engine stumble, and turning on the boost pump usually brought the pressure back up. I finally found that the flow restrictor in the return line that goes from the "octopus" on top of the engine back to the main tank was totally plugged. I cleaned it out and haven't had a single problem since.
The following user(s) said Thank You: garrett

Please Log in or Create an account to join the conversation.

  • Solarguy54
  • Solarguy54's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
5 months 1 day ago #18902 by Solarguy54
Replied by Solarguy54 on topic Intermittent Low Fuel Pressure
Thanks! I’ll check it out tomorrow.

Please Log in or Create an account to join the conversation.

More
5 months 14 hours ago #18906 by garrett
Replied by garrett on topic Intermittent Low Fuel Pressure
Yes, thank you I am going to check it out also.

Please Log in or Create an account to join the conversation.

More
5 months 13 hours ago #18909 by bstrachan
Replied by bstrachan on topic Intermittent Low Fuel Pressure
The restrictor in the fuel/vapor return line is actually a Mikuni carb jet that screws into the "octopus". If you release the clamp on the return hose and pull it off, you'll see the little brass jet. I forget what size drill I used to clean mine out... whatever was in there was SOLID. On my engine, you release the hose clamp by prying on it with a screwdriver. Replace it by squeezing together with a pair of pliers. Good luck!!

Please Log in or Create an account to join the conversation.

  • Solarguy54
  • Solarguy54's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
5 months 9 hours ago #18912 by Solarguy54
Replied by Solarguy54 on topic Intermittent Low Fuel Pressure
Sure enough. There was a tiny bit of hose debris clogging it up. Thanks!

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18945 by bstrachan
Replied by bstrachan on topic Intermittent Low Fuel Pressure
You're welcome! I hope this fixes your problem. Let us know, OK?

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18946 by garrett
Replied by garrett on topic Intermittent Low Fuel Pressure
Hi Barrie, I checked my restrictor port on Sunday and it was clear. But, it has not been acting up lately either. Thanks again for your insight on this problem which has been an issue for some Rotax installations for years. I can't find it in the annual condition checklist, it should be on it.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18953 by jiott
Replied by jiott on topic Intermittent Low Fuel Pressure
I have checked my return restrictor jet several times and it is always clear; yet I continue to occasionally get low fuel pressure warnings on WOT climbout.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18954 by Roger Lee
Replied by Roger Lee on topic Intermittent Low Fuel Pressure
What plane is this? Do you have an electric pump? Did you install the restrictor or did it come from the factory already to go? If it has a spec faucet electric pump at 3.5 gpm they are learning this may not be enough and you could go to the next larger size. Plumbing too may have an influence on pressure and the obstruction could be any where. Could even be in a check valve if you have one.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18955 by jiott
Replied by jiott on topic Intermittent Low Fuel Pressure
This is a Kitfox SS7, with high wing fuel tanks, gravity flow, and no electric fuel pump-pretty common for Kitfox. The 912uls was purchased new in 2013 and I purchased the return restrictor/fitting from Lockwood and installed it, and yes the restrictor jet size has been checked and is the correct size. Fuel flow tests have been done at the carburetors and just before the mechanical fuel pump, always indicate OK. A mechanical pressure gauge has been installed to check the digital readout and they both agree even during the intermittent low pressure. As you can see, I have been fooling with this issue for years and finally quit worrying about it because it never affects the engine power even for an instant. I have quite a trail of forum postings on this issue several years ago if you care to search back.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18956 by bstrachan
Replied by bstrachan on topic Intermittent Low Fuel Pressure
Have you replaced your engine driven fuel pump with the new style pump? There was a SB or somesuch on this years ago... I replaced mine but it didn't fix the low fuel pressure issue. But my problem was vapor locking, caused by the blocked return line. Sounds like yours is something else.

The Vans RV-12 fuel system is similar to mine and a lot of other low-wing Rotax powered airplanes. However, Vans wires the "aux pump" direct to the master switch so it is on all the time. I suspect (!) they did this to combat the common low fuel pressure complaints that many similar airplanes have. Does turning on your aux pump bring the fuel pressure back up?

The POH for my airplane specifically says NOT to use the aux pump for takeoff and landings.... how this plays out with the RV-12 setup is not clear.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18957 by bstrachan
Replied by bstrachan on topic Intermittent Low Fuel Pressure
The plot thickens. I hadn't heard of any high-wing aircraft having this problem. I agree, I never had any engine performance issues when the low fuel pressure light was on. I tried to get a spec on fuel pressure requirements for the Bing carbs but wasn't successful. But our experience would indicate it's a non-problem although I found it worrisome.

Are your fuel caps in good shape? My buddy had a leaking fuel cap on his Flight Design CT.... the slipstream sucked all the fuel out of that tank while he was flying over the Grand Canyon.... he didn't say anything about low fuel pressure though. Might be something to check anyway.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18959 by jiott
Replied by jiott on topic Intermittent Low Fuel Pressure
Barrie, my engine has the new style fuel pump, and yes I have checked the fuel tank cap gaskets. In fact some time ago I replaced them with the high quality Mercedes Benz gaskets that many people recommended.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18961 by Roger Lee
Replied by Roger Lee on topic Intermittent Low Fuel Pressure
Oh sure James, Answer all the questions and make this a tough one. LOL

I'm going to have to give this some more thought. Doses this happen to other Kitfox's like yours?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18962 by jiott
Replied by jiott on topic Intermittent Low Fuel Pressure
Yes I have heard of others in varying degrees. When I was posting a lot on this several years ago, it seems there were quite a few others in a variety of aircraft that chimed in with similar symptoms. I have always had a suspicion it has something to do with the pump (new style); maybe a tendency to be on the verge of cavitation at Max rpm. Maybe it can suck in a little air from the vent line under certain conditions.

Please Log in or Create an account to join the conversation.

More
4 months 4 weeks ago #18964 by garrett
Replied by garrett on topic Intermittent Low Fuel Pressure
On the old style fuel pump that had the weep holes top and bottom, I would put a drop or two of engine oil from the dipstick on the top weep hole if the fuel pressure started to drop, and this would bring the pressure back to normal for about 10 hours. What this meant to me was that the plunger shaft was getting galled up and sticking due to a lack of lubrication. Also during a gearbox inspection and cleaning the fuel pump eccentric was damaged from pounding on the end of the pump plunger.

Please Log in or Create an account to join the conversation.

More
4 months 3 weeks ago #18974 by Roger Lee
Replied by Roger Lee on topic Intermittent Low Fuel Pressure
This can also be fittings in line and even though the spec for an electric pump was 3.5 gph that at times is not enough and plumbing may be part of that issue. Very rarely do owners take into consideration that fittings and plumbing play a part in final fuel delivery.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

Please Log in or Create an account to join the conversation.