My Signum cdti had a fault thought it was a dmf, but turned out to be an injector, seemed as though it was running on 3 cylinders, lost about 15mpg, and shook the car when I put my right foot down. does a f***ed injector normally do this? Thankfully it was covered by my warranty, only had car 6 weeks ( love it ) ,big question do I buy a year or more warranty. My pride and joy is a 2006 Signum 1.9cdti Elegance.