I have a 2001 F350 diesel 7.3L crew cab. Since the cold night, I’ve been using my plug-in heater at. In the mornings it starts fine. But after 8hours of work (where I can’t plug the heater in), I have to get a jump to start it. Batteries are good and oil has been changed. Any suggestions?

Fuse number 16 on the fuse block

Have you checked the fuel pressure on it? Fuse? Pressure to the engine?

i have a 1994 f350 diesel 4x4 the engine wont start

you may have to flush the fuel system completely and use new fule filter, that also means the injector lines, diesel fuel tends to absorb more water than gas, then purge the system, make sure the glow plugs are working, new oil in the crankcase wouldn't hurt either

First, for poor starting from cold, you need to check the heater plugs, to do this, remove the wiring to each heater plug, then get a piece of wire/cable and get another person to help, you need to hold one end on the top of the heater plug, where the wire was connected, and get your assistant to flash the other end of your wire on the positive terminal of the battery, now, if there is a spark, then that heater plug is ok, if there is no spark, then that heater plug is faulty and should be replaced, do this to all heater plugs, and replace as necessary. Ideally , if just one is not good, then i would advise to replace all..
As for smoke from start up, all diesels will smoke on initial start up but it should clear when warmed up. However, if you have constant smoke, presumably black smoke, then you should check the air cleaner and hoses first, that the filter is clean and that the hoses are not blocked, split or collapsing when you give a bit of revs to the engine. The next step would be to check the fuel filter,if it has a drain plug, then undo that and see if the fuel is discoloured or you see any debrit coming out, it would be wise to change this , unless it has been changed recently. If you still have smoke, then you need to get the injectors checked, this can only be done by a diesel fuel workshop. Hope this helps

There should be a starter relay up by the battery on the inner fender, right side of the vehicle. There is also a starter solenoid on the starter, correct? I'm going to ask if you have it in park, neutral or the clutch pushed in, if so still no crank? On the starter relay, on the fender, there are 2 large teminals and 1 small. With vehicle in park or neutral and brake set pull the small wire off and using a jumper lead put 12V to the small terminal, the engine should crank. If so now check and see if you have power to that small wire when you turn the key to start. If not it could be the neutral safety switch, clutch switch (manual trans) or the ignition switch. There is also a fusable link that comes off the starter relay that could have blown. Do you have power to the ignition, do the lights come on, on the dash, when you turn the key on? If so the fuseable link is probably OK. If it don't crank by jumping the starter relay the problem is between the relay and starter. That relay sends a signal to the starter solenoid.

Diesels are famous for hard start when cold. Consider having a diesel shop install an engine heater.

Injector maybe but i'd check the glow plugs if they are not working in some cylinders it could act the same way, only allowing a couple cylinders to preheat the fuel mixture for easier ignition, if it runs fine after it warms up the injectors are probably ok

Do mean you have hard time communicating with a scanner at the OBDII connector, if so make sure you power at pin16 at diagnostic connector, also we have seen issue with glowplugs not working properly causing hard start when cold and starts fine after warm-up
You can check for glowplugs operation at initial key-of before cranking by checking for voltage at each glowplug connector with a multimeter.