I have a 2002 F550 with the 7.3. It will not start in the morning unless I plug in the block heater for a couple hours before. Once started, it runs great and will start up fine the rest of the day. I have replaced the glow plugs, both relays, fuel filter, valve cover gaskets and harnesses. Now a mechanic is telling me that it needs injectors and wants about $2,500.00 to fix them. This doesn't seem correct. If it is the injectors, why will it start and run great once it's warm? That doesn't make any sense. Just will not start in the morning unless block heater has been plugged in for a bit

This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1415281

Try using full synthetic heavy duty diesel oil and a Motorcraft oil filter.