will not start on a cold day

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3.3 litre engine will not start on a cold day . on a warm day starts right up sounds like its out of time backfires and smells of gas.getting code that says catalyst below efficiency bank 1 ...fuel pressure show 60psi when running but when you turn it off it eventually drops below 40psi ..have changed camshaft sensor crankshaft sensor plugs wires coil computer module ect sensor cleaned idle air control and throttle sensor cleaned map sensor..any ideas please help