Er, I do appreciate what you've tried to get me to understand! Sorry if I didn't come across that way.

Some of them agonize cos they "only" have a 3.0 with as "little" as 235hp LOL
(if that's the hp)

Now.... this Stig guy.....

 

I dont know what to make of all this as although mine runs good on normal unleaded it runs even better on shell V power (that's 95 UK and V power 99 UK I think) deferentially better response with the V power so now I m realy confused with you talking about 91 octane being the one the car is designed for

 

See above.

 

OK I get that bit 91 = 95 UK
the bit I don't get is according to the posts I should put 95 UK in my car even though it goes better on the 99 UK stuff

 

Nobody was telling you what to use. Make up your own mind, based on fact and experience. My posts were an attempt to dispel some of the myths. This (shamelessly stolen from wikipedia) might help:

Generally, octane ratings are higher in Europe than they are in North America and most other parts of the world. This is especially true when comparing the lowest available octane level in each country. In many parts of Europe, 95 RON (90-91 AKI) is the minimum available standard, with 97/98 RON being higher specification (being called Super Unleaded). The higher rating seen in Europe is an artifact of a different underlying measuring procedure. In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in Canada, the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in Canada and the US, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90–91 US AKI=(R+M)/2, and deliver 98, 99 or 100 (RON) (93-94 AKI) labeled as Super Unleaded - thus regular petrol sold in much of Europe corresponds to premium sold in the United States."

Accordingly, it might be that UK cars are tuned for the equivalent of our 93 octane gas. Maybe the Canadian versions are too, but I've run from 91 up to 94 in my own car and can't say that I did enough full throttle accelerations to really notice any difference.

Again, please don't fall for the myth that high octane gas has all sorts of magical powers. It only helps offset detonation, nothing else.

 

The errors I was getting were P301, P303, and P305. The tech said that a change to Exxon gas at the 91 octane might help or the change up. Since the nearest Exxon station is several miles away, we've hit on the strategy of mixing the gas. (There were three other codes but they seemed to be only generalized.)

The tech also recommended cleaning the injectors but I pointed out that they'd been cleaned something like 1,000 miles and 6 weeks previously.

Eric

 

thanks for the clarification
seeing that our cars may be calibrated for different fuel it would confuse the question posed in the beginning, therefore you may wish too disregard my experience btw I originally used V power for its cleaning properties in my Ford Mondeo V6 and found the performance improved so have used it since, I have tried a few tanks of normal unleaded in the Jaguar and noticed a very small drop in performance so back to the high stuff.

 

Toller, if the car is supposed to use 91 and you were using something less then that MAY be the cause, but P0301, P0303 & P0305 (don't drop the 0s) are misfires all on the same bank so I'd be looking for a common cause if they come back!

 

One of the myths I referred to earlier is the supposed 'cleaning properties' of one gas/petrol over the other. Put as much credence in those claims as you would 'new improved' laundry detergents.

 

94 octane will do nothing for your car other than the benefit of the extra cleaners. Your engine will not recognize the higher octane and advance the timing. 94 is often used by those who have the chip done and have the fuel mapping optimized for 93 octane.

 

Better to use the specific cleaning additives and stick to 91 (unless you've a remapped engine).