My truck has started setting the P0304 code when the temperature drops, usually first thing in the morning. After engine and air temp warm up, no problems. I replaced the coil, what else could it be?

 

Truck details, please? Year, engine? Miles on it? Miles on the spark plugs and the rest of the coils? What brand coil did you use?

 

Sorry, 2012, 5.0 V8, 230,000, about 70k on plugs, coils are original, replacement was Motorcraft

 

It's about time for new plugs, and maybe more coils. Are you sure you replaced #4 coil? That's back cylinder passenger side.

Other possibilities are injector or compression (valves).

 

I’m just got my truck back from exact same issue .

140km on new warranty engine due to same issue but cylinder 8 .

so same issue , turns out exhaust valves burned , rings worn and cylinder head was glossed up . Long story short on my 2012 5.0 , needs a lot of labour and parts if I want to attempt to fix . IMO common problem with these engines , not worth the 5-6 thousand fix .