ROTAX 912 ULS Fuel Pressure issue

Hi There

We are having fuel pressure issues that seem to occur on hot days and after the aircraft is flown and stood for a while.

On 2 separate occasions one of our members experienced a sudden LOW FUEL PRESSURE when full power was applied for take off, luckily there was enough runway left to abort take off.

And today I flew 100nm cross country without incidence, got to my destination & tied down the aircraft & used the canopy cover.
On our return flight at about midday of the same day with temps in about 30 Celsius we departed.
As soon as I completed my after take off checks I switched off the electric fuel pump and got a low fuel pressure warning and a whiff of fuel in the cabin. I immediately put the electric fuel pump on again and fuel pressure returned to normal. I completed my return leg and when I was taxing back to the hangars I tested the fuel pumps. As soon as I switched off the electrical pump the pressure would drop until it was in the red and the warning would sound. When I switched the electric pump on fuel pressure returned to the green range.
It seemed to me as if the mechanical pump was not functioning whatsoever.

The strange thing is, as I said above is that it only occurs on hot days and after the aircraft has flown and then rested. My flight to my destination was textbook but flown in the early morning.

Can you offer us any suggestions?

We feel it might be a vapor lock but the RV12 does have a return fuel line that should prevent vapor lock.

Kind regards

Justin Byrne

Search

Justin, you will find quite a bit of info on this subject in a word search of the Forum.

Your symptoms match those I experienced two years ago. After much testing--including multiple temperature probes under the cowl, I concluded vapor lock was not the culprit. Even though Rotax insists that leaking fuel is the *only* indicator of a faulty fuel pump, replacement of said pump solved the problem. If the new-style fuel pumps have a problem, it is occasionally setting off the high pressure alarm at low RPMs.

Jim
RV-12 #264 flying 154 hours

Thanks Jim!

Our annual inspection is due along with the new service bulletin involving the side skin stiffener, so we will have a look at the routing of the fuel lines and anything obvious then.

If we don't see anything i think i will recommend a new mechanical fuel pump to our group.

Thanks for you response and im glad you got yours fixed

Justin,

You didn't say whether you have the old style pump or the new. If it's the old style, I would just replace it with the new style. That will probably solve your problem, and also provide some peace of mind.

Keep in mind there is another on-going issue with false high fuel flow indications at higher altitudes when the electric pump is running. But it sounds as if you already have a switch installed on the aux pump, so you should not see that problem.

PS - Please send some of that warm weather our way!

John

LOL hot isn't the word it was has been down right cooking down here!

Thanks, i have read a few of those discussions and it seems new and old pumps are problematic. To be honest i'm not sure which pump it is, i have asked the other members if they know.

We built the RV-12 in groups so the guys who worked on the engine will give me an answe r shortly.

Yeah we have a switch on the aux pump and only typically use it for take off, landing and on HASSELL checks before stalls etc similar to our certified type brothers.

I would unscrew the line at the fuel pressure sensor and see if it is clogged.
It is an easy check.
See here:
http://www.vansairforce.com/community/showthread.php?t=93324