When I had my car dyno tuned I had been running on Shell V-Power for some time. Recently I switched over to BP Ulitimate and the car ran much rougher especially at low rpm, I ran with it for two tanks from different stations just to make sure I didn't imagine it. So is there enough difference in fuels to throw the PFC map off if you switch, both are 93 octane. The only choices around me are Shell, BP, Mobil and Citgo.