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A quote from a thread discussing the merrits of BP Ultimate 102 ron fuel:

fletchie55 wrote:I think the ECU can only advance and <beep> the timing by a maximum of about 12 degrees.. or so I remember being told. if you put in 102 fuel, the timing will be advanced as far as the map has allowed the ECU to push it. If you had the car re-mapped specifically for that fuel you may get more advance still, but you could also run into problems if you ever needed to run the car back on 95 as the ECU may not be able to pull back the timing enough as it only has a limited 'window' to move the timing within.

Can a tuner or someone with similar knowledge enlighten me on points above?

Basically on a remapped S4, my car with a custom map done on 99 ron fuel if we need an example, be likely to be able to advance the timing enough to benefit from a 102 ron fuel or will it have been mapped to adavnce as far as the merrits of 99 ron fuel and othersie be tuned to safely <beep> and run on the more popular 95 ron fuel available?

The details interest me, but in reality using the fuel will only be a once off or extremely occassional thing, but even so not worth wasting even £100 on a single tank if the theory is the won't be able to benefit from it.

If there is a maximum +/- advance or <beep> the ECU can handle, is there a block that can be measured with vagcom to see what the +/- figure is on the fuel we are currently using?

I fear this is either complete jibberish or at best barely understandable by someone that actually knows what all these terms are, so excuse me.

Graham

i think markB done some timing logging-adjusting in another thread..

If the ECU isn't pulling back ANY Timing at all on 97/98RON, then it won't advance either if you run 102, full stop.

Thanks. Could save me from an expensive experiment! I think that BP 102 is £2.40 ish a litre!

I am thinking I could look at block 022, 023 and 024? If on current fuel I am seeing a few degrees of <beep>, then there is the potential for it to advance, correct?

So if at the same time as having a good FATS time, I am also seeing a few degrees of <beep>, it's really a good thing allowing for improvement should I get a better batch of fuel?

Likewise I could try 97 ron fuel instead of 99 and see if the ECU retards any more or not.

Anyone with vagom already been there and done these experiments before? Any results to share?

took half a second of my fats time after adjusting my timing. Went from no retardation to about 4deg max. car running much better now

So am I barking up the right tree with the blocks I mention above? In your other thread I think you mention 2 differnt blocks.

I won't be adjusting anything, just might try some other fuels if the ECU is pulling the timing back with the hope a different fuel may be better.

You want to log the 2 blocks that log CF's. Can't remember the numbers. first one does first 4 cylinder, second does the last 2. If I remember correctly...

Did a quick log earlier. Running on a full tank of fuel which was a quarter tesco 99 and 3/4 v-power.

I am getting some retardation at certain points in the rev range, a little bit random, but anything from 1.5 to 5 so from what's been said so far sounds like thre is room to take advantage of better fuel.