For the last while I have been having backfiring issues with my quad. It's a 2012 550 arctic cat EFI. It's the second time it has happened. The first time a new air temp sensor fixed the problem. Now, about a year later it's doing it again. The mechanic tried a new air temp sensor and a new spark plug. Neither worked. He says it's probably the ecu that's the problem, and that it costs over $600. That seems rather high to me. Is that really the going rate for the ecu for my quad? Will I be able to find it on amazon or ebay? If so, what's the part number? And is there any other models that have the same ecu? Any other ideas as to the likelihood of it being the ecu? What do you figure the chances are of having got a faulty replacement air temp sensor? Thanks!