Hi,

I have a moderately remapped Octy II TFSi VRS which seems to have dropped in power and MPG - nothing drastic, but notable. I have also had one or two 'clackety' starts when starting the engine from both cold and warm. The only thing that I can think of that would correlate with when this started was filling up with BP Ultimate 97 RON fuel before the weekend. Previously I used 99 RON from Tescos.

I know that a remapped engine should use premium unleaded but I would have thought that BP Ultimate would cover this and would be surprised if there was not good control of quality in the UK. I was therefore wondering if anyone else with a remapped TFSi had experienced problems with this or a dodgy batch of premuim unleaded in general and did it cause similar symtoms?

I don't think fuel is your problem but more likely to be a diverter valvle failure. Quite a common issue as thse tend to split especially with remapped cars causing a lack of boost but there is a newer version which corrects this issue or there is an aftermarket one from Forge.

Definately worth getting checked out

More details on this and loads of other stuff can be found within this sticky thread

Thanks Makefish

I considered this possibility and certainly haven't ruled it out. However, I am not seeing the big drop in boost that a DV failure would suggest. If anytrhing, the symptoms are more like the Positive Crankcase Ventilation failure described in the link you gave (but without oil on the filler cap). I also considered the MAF sensor.

I guess it could be a bunch of things. I just wanted to rule out the dodgy petrol idea since it coincided (sort of) with the issue. I guess the easiest thing there is run the tank low and fill up at Tesco again!