I have a 1978 300cd that is experiencing loss of power problems. The problem started with a knocking noise that eventually got louder....i noticed loss of power a higher speeds ....sometimes difficult to start...i looked at fuel injection pump and noticed a smeall leak towards the front of the pump...not sure where to start before taking it in for a checkup......any help would be appreciated....

Run round with a stethescope to see where the noise is coming from.

You may have to do a compression test . Valve or piston/ring problem?

Good luck.

Change your fuel filters.