I don't know the year but if it has a hand primer try pumping it a hundred times or so before starting. Could be you have a leak in the fuel system that is lettin in air. Although you probably cranked it enough to get any air out...

No fuel out the line is a question there. if you have fuel to the pump then you will get fuel to at least some of the cylinders. try lossening the other lines and see what you get too.

The other obvious thing is low compression and glow plugs that aren't working right. With either scenario you could have problems. With low enough compression glow plugs won't help either.

Could also just be a low battery that is not cranking the motor as fast as it should or the starter is not up to snuff and not cranking fast enough to light her off.

try charging the battery really well and see what happens, also check the glow plug resistance at the plug in the relay. should get .05 to .06 ohms there. Might have a couple of bad plugs.

Good luck.

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique