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Originally Posted by MNBoxster
Hi,
It's absolutely a possibility. Winter fuels are rich in Butane and Oxygen because they are cheaper than adding other Octane boosters such as MBTE, Alkylate, and ETBE.
Because the need to meet RVP (Reid Vapor Pressure) mandates by the EPA lowers due to winter temps (allowing the use of Butane and Oxygen and still meet mandated RVPs), refiners switch to Butane and Oxygen in greater amounts (because it is cheaper to produce). This can trigger a CEL because the values lay outside the DME's pre-programmed OČ Sensor values.
Since lower Octane fuels require a lesser concentration of these chemicals, they will prevent a CEL from occuring and the concequent defaulting of the DME.
Because the ambient temps are considerably lower during this season, the detonation threshold is also reduced. You may actually be OK using these fuels and the sensors will return to normal operation in the Spring. In theory the guy's correct, but in practice? Only making the switch will tell...
Happy Motoring!... Jim'99
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If it were sensative to this, it would be a widespread problem with all Porsches. It would also not be helped by switching to a lower octane fuel. I don't believe this is his problem.