Not really framiliar with your year etc or having a cat but make sur you spray it with some "force" or some kind of penetrating lubricant . I know my 735i exhaust would not com off with a air gun and was worried about braking it but ended up with a socket on an extension with breaker bar and pipe with a friend holding while I put leverage on it good luck . Spray it or what ever the night b4 and again in morning and tapping it between spays seemed to help me .