2001 ford 250 s/dv-10turns over fine. wont start sometimes.when it starts it runs fine.seems like cold weather makes it worse.if it starts it wont die.started about a month ago and getting worse.

How to Start a Car in Freezing Cold Winter Weather

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wikiHowFreezing cold weather can take a toll on car batteries. ... It's much more difficult to start a cold car with a mostly-empty tank, so do yourself a favor and gas up ...

Why is it so hard to start a car in the winter? - HowStuffWorks

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To start a car in winter, your engine has to work extra hard. Learn the top 3 reasons your car is hard to start in cold winter weather.

Debunking 5 Cold-Weather Car Myths - Popular Mechanics

If jump start always works, the problem is the battery or poor connection to the battery.

Lube the starter pinion with graphite in stead of oil or grease for cold weather

sounds 2 things here. fuel pressure regulator or the idle air control valve. I an goingwith idle air control valve

Timing belt being off one tooth will not cause this problem but rather loss of power and hard starting all the time,

in the cold it will not start, the engine will spin but wont fire is this correct?

There are many things that can cause this, a little testing will be needed, the first thing that comes to mind with the ford and cold weather is the coolant temp sensor, it give computer a false reading and can cause hard starting or even no start, a scan tool would be helpful to see what temp it is give computer.
The best way to narrow this down to to check for spark when it wont start, a weak coil in cold weather will cause this problem or bad coil wire to cap, but if you can see if it has spark and let me know,
another test is to check fuel pressure, to see if it is getting fuel, and the fuelpump relay,

Let me know if it has spark or fuel when is does not start, good day

Without being able to see it, it is hard to tell. But anytime I ever hear problem is worse with water, I look to the electrical system. I would look into replacing the rotor button and distributor cap as a start. Fuel injection or carburetor?

How old is your battery? If it is the original 2006 battery now is the time to replace it. A battery needs to be replaced after about 4 winters. Cold weather reduces the battery capacity and makes it harder to start. If you wait the car may not start at all.

check the fuel pump and see is working properly, if the pump is good than the problems will be the crank sensor is faulty. what crank sensor does it sense the turning of the flywheel and it send a single to ecu, and ecu send a flow of power to turn on the fuel pump as long it sense the flywheel turning.

change distributor cap first and see how it goes could have a crack in it.Failing which you need to test the ignition module when its cold as sometimes a component will break down and not work when its cold ,this is very much a hands on type job so if dist cap doesnt cure it call a mobile mechanic

I had a similar problem with my 1986 300e , which got progressively worse until the car was no longer driveable, I changed out the fuel pump relay and the problem went away.