Bigpower

Just something that I have noticed whilst mapping recently that a map done for Tesco 99 that is completely knock free will, if left in the car for a period of time unused will then start knocking a couple of degrees here or there.

I havent noticed the same with Shell vpower.

I know that fuel loses its octane gradually and that race fuel is particularly prone to this.

That's worrying as my car sits for weeks at a time, especially at this time of year. I also carry 20L in a can, that may also be unused, including through the season.

Be keen to know your findings on this Dunk.

I only spotted it the other day Gerry then looked back through logs.

When the map was done it was knock free (say on a saturday am)

But consistently logs from mid week (the week after) showed a couple of points where there was some knock. Not much.. but retardation all the same.

I wonder whether the ethanol in the Tesco has a shorter in tank life and the octane of the 99 reduces.

I will see if I can properly replicate the test with vpower.

[geek mode]
I have noticed that there is a 3% difference in closed loop fueling between the two as well which carries forward into open loop.
ie.
if mapped on 99 and it wants to take out 3% fuel if run on vpower.
if mapped on vpower - it wants to add 3% more fuel for tesco 99 because it considers it is running too lean.

I now have two maps - one vPower with injectors at 867cc and a tesco99 at 842cc to account for the stoich differences in fuel.

[/geek mode]

:-D you are a geek .... could weather have an effect, outside temps etc?.

it could do

both days were 5C external ambient temp and both as crisp and dry as st stevens pizza.

But you would expect to see a small difference between the two with Tesco having 5% methanol although it should be less than 3%

Tesco 99 Octane contains bioethanol

[quote="dynamix"]Tesco 99 Octane contains bioethanol

Indeed - I would have expected that difference

I didnt expect to see rapid deterioration of the fuel quality in the tank though. (if it was that and not my mapping before anyone says )

So, how will you dis/prove the deterioration theory?

You won't be able to conrol samples or conditions.