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Low Fuel Pressure on take off

B

ben barron

Well Known Member
I have had a lingering issue. Occasionally (~2 out of every 10 takeoffs) I get down to 2.1psi fuel pressure on takeoff (yes the alarms go off). I have replaced the fuel sensor, cleaned the Gascolater & fuel filters, and checked the banjo bolt. I use Mr. Filter when I fill up every time with ethanol free fuel. The Rotax does not sputter or seem to be starving for fuel when this happens and the pressure comes up a minute into flight. Any ideas?
 
I have been having the same problems for a year

Mine are less frequent, and may possibly (not satisfied yet) may only occur with a rather rapid application of throttle. This seems to be a very common RV-12 problem. My next place to look is for a bad connection where the wiring bundle plugs into the D180.

Wayne 120241/143WM (360 hours)
 
Mine was a bad connection at the fuel pressure sender. The one I have uses push-on connectors; I had to remove them, squeeze them closed a little and put them back on. Nice and tight, no more low fuel pressure alarms. I think some have a different arrangement that uses ring lugs to connect the wires instead of push-on terminals.

Edit: MY bad. What I was getting were high fuel pressure alarms, not low. Please disregard anything I said. I should know better than to respond to a post here while half-listening to a conference call.
 
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I have the old style fuel pressure sensor with the spade lugs. I used spray contact cleaner and spray contact lubricant on the terminals - both from HomeDepot. I also "tightened" the squeeze on female connectors and now everything playing nicely together again.
 
But the new fuel sensor doesn't have push-on connectors

It has three wires coming out of the sealed sensor; you cut the old wires and splice them to the new ones. I don't think all of us have done bad splices.

Lockwood says they have had "several" reports of low fuel pressure warnings, all on takeoff, and all from RV-12s- - no other Rotax-engined birds are reporting it. They don't have a clue either.
 
My current solution

is to set the "bottom yellow/top red" value for the fuel pressure sensor alarm to 1.0. If the engine quits one day I'll know it was the wrong one.
 
yankee-flyer said:
is to set the "bottom yellow/top red" value for the fuel pressure sensor alarm to 1.0. If the engine quits one day I'll know it was the wrong one.
Click to expand...

That may not be in your best interest.

You might want to actually verify what pressure your running. Perhaps install a temporary mechanical dial gauge. Probably find a 0-10 psi gauge on eBay. Maybe a T fitting and a length of tubing thru an existing hole in the firewall so you can monitor in the cabin for a few flights.

My problem was high fuel pressure. Low fuel pressure would be very worrisome indeed...
 
Van's response

We?ve seen/heard of this several times.
It?s more likely when the engine is warm and the fuel tank not full. 2.2 lb seems high as the minimum pressure. Lycoming carbs min pressure is 0.5psi. As you see, the Rotax will run happily at <2.2psi, and typically the pressure will not drop much <2psi. Climbing is the worst case scenario as the engine is now higher than the tank and the fuel demand is greatest (high flow = lower pressure).
My guess is that individual installations/conditions vary and can cause this. You?ve got different pumps, sensors, differing types of fuel, amounts of fuel, tank venting, climb angle, temperature (OAT and fuel/engine temps), even variable resistance/voltage to the sender ? the list goes on. If the alarms are a concern, setting the value to say 1.8psi will probably eliminate most of them while still preserving the feature if the fp does drop enough to stop the engine.

Vans
 
fuel pressure

I posted a thread on this on 2/7 but nobody noticed so am hitching a ride on this one./ I have a pressure problem that the dynon tells me is low but the dynon pressure showing up is over 5 and well into yellow. I know these things get goofy now and then but I feel more comfortable if the psi is where it belongs I have also learned that dynon now supplies a sensor called a Kavlico. but there seems to be just as much trouble with those as well.
So I just ordered a new old style (100411-000) as they still have them at dynon and aircraft Spruce sells them as well (10-05471).After all the first one lasted 5 years and 300 hrs.\, I am also going to test the psi by temporaily placing a good sensor gage in the line and if it looks ok will probably install the new sensor when it arrives. One more thought I had is the old sensor has an internal ground so it's grounded when you attach it to the firewall so I plan to add a ground wire from an appropriate location and to the sensor at the mtg point. I suspect that might solve the problem, but will have a new one just in case it doesn't work. I would be interested in your thoughts on these steps and any other ideas you folks might have, Thanks,
dick seiders 120093
 
Grounding the fuel pressure (original) sender case will not hurt anything, but I do not think that it will help either. The brown wire is grounded that comes from pin 10 of the D-180 control board firewall connector. Chances are that the case is insulated from the internal electrical components.
 
Dick, is the fuel pressure reading OK

WHILE the alarm is going off? If I take the time to assure the engine is running OK. look for a landing spot, turn off the alarm, and then bump through the screens to get to the pressure, screen, sometimes all will be well by then. It's a pretty short-term whatever it is.

I can't duplicate the alarm at will, but it's always on takeoff, usually early in the climb when the nose is very high to keep airspeed at 75 (or under 80 until I can raise the flaps), and may possibly be associated (more tests needed) with moderately fast throttle application )I.e., rapid airframe accelleration). If you install the Kavlico sensor you need to install a capacitor (see John Bender's posts) and have version 5.4+ of the D180 software.

Based on above inputs (THANKS!!) I'll set the bottom yellow to something 1.5 to 1.8-- it was 2.2 when I was getting alarms.

Wayne 120241/143WM
 
No. The alarm was sounding low fuel pressure while the Dynon page was indicating max psi. ( all the way to the red) This occurred during ground engine run tesr, I tested with a gage that showed 7-8 lbs it it was a 0-100 lb gage so lower h
Readings are suspect. I then installed new (old style) sensor and at engine run (three min.) It indicated 5-5.2 psi
I am hopeful problem is solved, but will have to flight test to be certain.
BTW I have never exp. low psi warnings on takeoff full power.
Dick
Ps thanks Joe for your comment.
 
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didn'y fly today as wind gusts were messing things up so did some engine tests on the ground. The fuel psi was 5.1to 5.2 at 2100 rpm. After warm up ran engine frpm 2500 to4000 and the fuel psi dropped to 4.6 to 4.8. at 4000 to 4700 rpm psi was steady at 4.6. Aty return to low speed of 2100 the psi again went back to 5.1 to 5.2. There were no low fuel pressure alarms like those that occured with the old sensor.
I am comfortable with that result that the new sensor has corrected my problem. I will fly tomorrow and do a few climb-outs to see if there are variations to what I saw today and post the results.
dick seiders
 
fuel psi

Cranked it up today and limited it to another ground run-up as the pressure was all the way to 5.2-5.6 It would not come down like it did yesterday with an increase in rpm. So I went on a fuel psi search of VAF. I recall reading that the new pumps ran higher psi but that was a year and a half before I installed one as I waited the five years until change was recommended.
I found the answer in that VAF file with a thread from Tony t. on 9/3/2013 that showed the limits placed on the psi by Rotax. This was a concern to me as I didn't want to exceed their psi limits which are 7.26 psi and flood the carbs . This is a full 1.5 points below what I was showing with a reading in the fives. Thank you Tony.
The second half of the answer came from Jean-Pierre Bernoux on 9/5/2013 where he posted recommended new settings for the Dynon on psi limits oer category (red, yellow, and green).These settings were provided by Van's after checking out it's red Rv12. Thank you Jean-Pierre and Vans.
I did all of the above went flying and the indicated pressures were as they should be. Problem solved.
BTW I checked the psi thru-out the flight under all conditions including climb-out and the were no issues.

I am grateful to all who helped by posting this stuff, but have one question for Vans. Why did you not just issue a Notification with the data and every 12 driver would have been alerted, and avoided the whole "search and see if you can find the answer" to an important problem?
dick seiders 120093
PS I am very happy with the info thank you all.
 
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one more thing for those who are seeing lo psi readings put a psi gage in the line to see what the real psi is I suspect it will be as advertised in the Rotax data from Tony. Re set your Dynon EMS under fuel pressure.. If still erratic like others said earlier look to solving your problem by trying to fix the present sensor by assuring the connections are in good shape. You may be able to avoid buying a new one.
dick seiders
 
Sorry Wayne I have been unable to find the posts again as well. When I get to the airport I will reproduce the info for you as I wrote it down. I do recall Tony indicated the Rotax limit for high prssure was 7.26 lbs. So Dynon can be safely recalibrated to 5.8 top green arc with the new pump.
Dick
 
Actually, just to clarify, I did not indicate the pressure limits for the fuel pressure, I just posted a page out of the Rotax Service Instruction that accompanied the release of the new fuel pump. It shows max. fuel pressure = 7.26 psi.
Here it is again:
i-TbC3MN6-L.jpg
 
low fuel psi on take-off

Wayne the numbers I used are alledgedly from Vans. I reset the Dynon as follows and the Dynon is now happy with the results over several hrs of flying.
0.7 red
0.7 to 2.2 yellow
2.2 to 5.8 green
5.9 t0 7.2 yellow
>7.26 red

dick
 
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