2005 Mazda 6s 3.0 cranks no start then backfired when it almost started .my buddy I bought it from thought cat converter or one of cats were bad . When it did run before I got it he said it would run then when it would warm up it would die It’s been sitting for 2 yrs before I got it .rear o2sensor wire were broke off I’ve noticed and has a poo37 code. Any ideas what possible could be wrong. going to drain gas tank to get old gas out put fresh in and change oil and spark plugs before go any farther thank you for any advise