No backfiring. I would assume that if fuel was in the cat or exhaust for that matter the exhaust might smell like the engine was running rich but it doesnt. Never backfired or anything. We dont take many trips longer than about 20 or 30 minutes in it and since we got it, its been getting pretty solid 18.2 mpg even with my wifes heavy foot on the gas.

Either was i am making a call to the stealer to get it in next week to get fixed.

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2002 X5 3.0i