I have a 1986 f250 with a 7.3 diesel I have recently installed since the first turn of the key I have had nothing but problems starting when its cold .the colder it gets the harder it is to start.now has a new injection pump all new o rings return line kit new mechanical fuel pump new fuel tank and all new fuel lines. Also installed new glow plugs and checked wiring harness for continuity.all checks out good but still hard to start when cold... can you please help.

Sounds like you have a cold weather diesel fuel problem. The link below may help:

https://www.askmehelpdesk.com/cars-t...ml#post1985158

I would also use SAE 5W-40 full synthetic HDDO--it makes a difference, especially in winter. There are several suggestions in Item 12 below:

https://www.askmehelpdesk.com/cars-t...ml#post1415281

Ensure both fuel filters have been changed and water purged. Check the condition and level of the oil--it can affect fuel pressure.