Hey, I have a 2007 4.0 V6 mustang that have problems starting when it’s cold outside (from +5 to -20 Celsius)
it will start in the cold if I use ether and run fine and start fine for the hole day but the day after it will not start on its own, but yesterday it wouldn’t even start with ether.
if it have been sitting over night in the warmed garage, it starts right up on its own.

I have replaced the fuel pump and spark plugs still the same problem.
there are no DTC codes. I tried to unplug the coolant temp sensor and MAF sensor to see if that was the issue but still same problem. Hope you guys can help me

 

It's amazing how many "Cranking Amps" an automotive Battery loses when very subjected to cold.
A 2 year old+ battery can drop from 800A to 500A very easily when in those sort of temperatures.
I always use a "trickle" charger in the winter to ensure battery is in top shape. One can also get heater pads for the Battery tray, which are common in places like the Pacific North West and Alaska.

 

Hey, the fuel pump only says a little noise when turning ignition on. And there is not coming fuel out.
when the car is warm after sitting inside the garage, it work fine. Where should I look?

 

Any decent battery should be able to start a car down to -20, if it's a problem at +5 the battery isn't the problem for sure. Could be a bad relay or something that's not functioning properly in the cold, or the fuel pump is just starting to go.