[quote name='ces' date='May 31 2005, 06:56 PM']sounds more like "pinking", which more than likely linked to poor fuel, do you use supermarket fuel?
Ever since having tuned engines when younger, always found they ran badly on poor fuel, have done all the "scientific" experiments, and convinced what you pay more for the fuel, rewarded in either more response or more mileage. Therefore you pay more and get more, so they balance themselves out.
If unsure, try replacing the engine after a few years of savings 3p a gallon, gues which one is cheaper?!
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What a load of rubbish

Do you think that the refineries have a seperate area marked cheap fuel! The unleaded you get at the supermarket is the same as at the regular stations. The only exceptions are things like Optimax but that said I'd be suprised if the supermarkets Super Unleaded wasn't out of the same tank.
A while ago I got chatting to one of the fuel tanker drivers about this and he said that he filled the tanker for the local BP garage from the same place in the same refinary as for the local supermarket. The olny difference was that he switched trailer unit for one with the corresponding logo.
There are 9 main refineries in the UK
BP Coryton
Stanford-le-Hope
Essex
BP Grangemouth
Grangemouth
Stirlingshire
Conoco Ltd
Humber Refinery
South Killingholme
North Lincolnshire
Esso Petroleum Company Ltd
Fawley Refinery
Fawley
Southampton
Petroplus
North Tees Works
Seaton Road
Port Clarence
Cleveland
Shell UK Ltd
Stanlow Manufacturing Complex
Ellesmere Port
South Wirral
Texaco Ltd
Pembroke Plant
Pembroke
Pembrokeshire
TotalFinaElf/Murco
Milford Haven Refinery
Milford Haven
Pembrokeshire
TotalFinaElf
Lindsey Oil Refinery
Eastfield Road
North Killingholme
Immingham
North Lincolnshire
You will find that despite them being owned by BP or Shell you will see tankers for all of the various retailers filling up. Do you really think that Total/Fina/Elf stations only get petrol delivered from the refinery in North Lincolnshire or that every Esso tanker you see started out from Southampton?