99 cummins turbo diesel 289k, runs good, somtimes wont start. usually after short trips. if i spin off the fuel filter or remove and reinstall plugs on top of fuel filter, starts. or if i let it sit overnight it will start. what is the problem here?

my bet is dirty diesel fuel, filter, whatever.
But that is assuming the glow plugs are functional.

Has the fuel filter been changed? It sounds like a fuel starvation problem. Not familiar with the Mercedes diesel I had a Dodge Cummins 24 valve diesel and had the same trouble when the fuel filter had gotten to dirty. Another issue could be the fuel pump itself is starting to go, not a usual problem but would cause the engine to cutout if it is not providing enough fuel. Which in turn would make it hard to to start after since there is not enough fuel in the system. Also check if there is a filter in the fuel tank could be plugged. Check the fuel also, see if it has started growing algae in the tank if this happens it will plug filters quickly. Good luck

Unscrew the filter canister and check for debris. If you haven't changed the fuel filter in a while it would be a good idea to do that as well.

Just to start with the basics make sure their is fuel in it ... somtimes when these trucks run out of fuel you have to add more then 5 gallons to get the fuel high enough to run over the internal cup that the fuel pick up tube sets in 1 or 2 gallons is not enough to do this . Then have some one try starting the truck while you remove the fuel cap and put your ear to the fill tube for the gasoline you should be able to hear the fuel pump run because it is located inside the fuel tank . If you don't hear the pump running you can try hitting the bottom center of the fuel tank with a heavey blunt object ( block of wood ,Baseball bat ect.) nothing that has a sharp edge . Do this while some one is cranking ( turning the key to start the truck) this somtimes will free the pump up and it will start working again . If it starts then you know the pump is bad . Somtimes when the pump frees up they work again for weeks or months but it not good to take that chance and break down on the highway. Replace the pump and filter .

Well, Hate to say this to you but your Cummins 24v turbo diesel does not have glow plugs. The fuel temperature necessary for proper ignition is heated by an element inside your fuel filter housing.

Actually this is a relativly simple fix, it is located near the diesel filter {R/H of engine} and is merely removing the feed lines and plugs, replacing the gaskets and pump, you will have to prime the unit before attempting to drive, be generous with the diesel when priming, as running them dry can be costly. replace the filter while your at it and remember to fill the chamber with fresh fuel before sealing it closed. Good luck, hope it helps.

Please don't forget to rate!!!!

Diesel Engines The 6.9L and 7.3L diesel engines use a one-piece spin-on fuel filter. Do not add fuel to the new fuel filter. Allow the engine to draw fuel through the filter.

1. Remove the spin-on filter by unscrewing it counterclockwise with your hands or a strap wrench.
2. Clean the filter mounting surface.
3. Coat the gasket or the replacement filter with clean diesel fuel. This helps ensure a good seal.
4. Tighten the filter by hand until the gasket touches the filter mounting surface.
5. Tighten the filter an additional 1⁄2 turn. NOTE: After changing the fuel filter, the engine will purge the trapped air as it runs. The engine may run roughly and smoke excessively until the air is cleared from the system.
   

You said you have fuel flowing from the inlet line of the injection pump? But not at the injector lines?

Did you check to see if there is power to the glow plugs if not then that may be the problem and if there is power when you cycle the key not to start but for the plugs to warm up you may have a bad glow plugs.