Fuel and fuel pressure problems
Hi Guys,
During the early 25 hour phase of flight time (Early summer so 35-40Deg ambient temps) i also experienced low fuel pressure alarms at higher altitudes but mainly with the electric pump off, (Yes i have a fuel pump switch and glad i have) so I turned the electric pump back on and accepted it would most possibly be vapour lock caused by high temps and altitude.
After a PM exchange with wingedfrog he suggested it may be a good idea to share my experiences on the forum also.
I raised the following questions with him.
I am not concluding my experience and remedy below will necessarily address other peoples issues, just sharing my findings and experiences for other to consider.
- Are you sure the mechanical pump failed?
- How did you confirm it had failed?
- What fuel brand and Octane rating are you using?
- Have you tried to run the engine again with the same fuel pump in a lower ambient temperature?
- Have you drained and refilled the fuel tank with fresh fuel?
The reason for my list of questions is i have experienced the same symptoms as your self, only i was off the ground in climb out off a short strip without enough room to land again on the remaining strip or suitable landing options or sufficient height to turn back both times, before i identified and remedied the problem!
The remedy was to add a minimum of 30% avgas to the fuel tank in hot weather.
Both times ambient temperature was over 35deg C airfield elevation 1,460' (electric pump on)
First sign of a problem was a strong fuel odour immediately followed by partial loss of power and low fuel press alarm. My reaction was to first turn off electric fuel pump,(Because of the strong fuel odour and fear of fire) the engine regained power then started to loose power again along with low fuel pressure warning, so it was electric fuel pump on and off to keep the engine running without flooding to level off get some increased airflow to cool engine bay and get some landing options. Next morning and days following in the cooler temperatures, i could not get the problem to reoccur. Another hot day weeks later a repeat of the same problems occurred. (during the flight prior, i noticed fuel pressure fluctuations with the electric pump off and to a much lesser degree with the electric pump on)
i had landed for a short break with engine shut down, then restarted and departed for the home field when the partial power loss occurred.
My local and only service station in the town was having difficulty with their 95 Octane fuel pump, we could only get fuel early in the morning when the temperatures were cooler. (I only realised the significance of this after the problems occurred)
I suspect they were still selling winter fuel, now in the summer due to low fuel volume sales turnover.
After the first power loss i dismantle the Carburettors looking for problems as to why i got the fuel smell, bowles were clean, floats weighed in correctly. Fuel pressures rechecked, fuel flow re-checked, fuel pump was only 30 hrs old and no sign of fuel from the pump telltale drain pipe.
After the second time and lots of research about fuel and the effect of variations in the Reid vapour pressure due to fuel blending for summer and winter fuels, i drained the fuel tank and refilled with 100% avgas 100. I picked a day over 40deg (plenty of those during the summer here) with delayed takeoff until temperatures were in the Yellow caution area, there was no issue. (My home strip is 2 km long, i had a plan and options)
After landing and allowing the plane to sit and heat soak for 15 mins with very high under cowl temps, the exercise was repeated with no problems, with the electric pump on or off the fuel pressure remained stable. I then experimented with different % Avgas/ULP mix down to 30% Avgas with no further problems in the hot weather. I now run with an Avgas/Ulp mix in the hotter weather with no further issues.
Cheers, Andrew.
