I had the app on my phone and it worked fine until I deleted cookies, etc. and can no longer log in on my phone, although I can on my PC. I thought I may have forgotten the password so I reset it to no avail. PC is fine but Android (Galaxy S4) is not.
Certainly bizarre but the only way I could do it is if I associated Fuelly with Facebook. I will not delete this post in case it proves to be helpful to someone.