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Reason for engine hesitation under acceleration

  • 2010
  • Cayman S
71 000

The engine hesitates very briefly under acceleration and this is most noticeable at around 2000 RPM but can occur at higher engine speeds. The strange thing is that the problem disappears when I fill the fuel tank with gas and reappears when about a third of the gas in the tank has been burned. The CEL does not come on and the car drives normally otherwise - the fuel consumption is also normal. I tried adding Jectron to the fuel and it seemed to work initially but I eventually realized that it was the full fuel tank rather than the Jectron or the brand of gasoline that made the problem seem to go away after I had refuelled. Whenever possible I use Top Tier gasoline so the fuel system should be fairly clean. The engine air filter was changed about 10000 miles ago and the spark plugs were changed about 25000 miles ago.

Could this be due to a weak fuel pump and/or a plugged inlet screen to the fuel pump? I have difficulty believing the slightly higher hydrostatic pressure at the fuel pump inlet with a full fuel tank could make such a difference in the fuel pump performance but it may be posible. Or could it have something to do with the fuel tank vent system?

Any suggestions on how to solve this problem would be most appreciated.

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