old fuel.........

[spatz]

as you might know I am running a ls7 on a DTAFAST ECU with only MAP control.
I still had fuel from last year in the car and noticed that the engine is not really running as I remembered from
last time. So yesterday I finally have been putting new fuel and to my surprise that changed the behaviour quite a lot.
So it seems that production ECUs can compensate somehow for older fuel since I never experienced that e.g. on my 993 turbo
that sees very little driving through the year and is also in winter hibernation for 5-6 months.
What happens with older fuel that causes this not so nice combustion ?

[anonymous-user]

If the car is stored, with only a small volume of fuel in the tanks (i.e not full) the "Light fractions" will tend to vapourise and escape. In effect, the overall fuel volatility will be reduced slightly. Usually this has the largest effect on transient fuelling accuracy, and can make the engine experience lean spikes on tip-ins etc. On production cars, the long term closed loop fuel trim is used to correct for fuel volatility changes (and they tend to now have a (semi)sealed evapourative emissions fuel system that helps limit off-gasing (due to the higher in tank vapour pressure)

[spatz]

yes the tanks were close to empty before end of season last year, makes perfectly sense

thanks