How do you mean, slow starting,
Slow turning over.
Or you have to turn it over for some time.
Slow turning over, check battery and all connections, to starter motor.
turning over for some time, maybe fuel injection, timing out, Most diesels do not need the glow plugs, they will start without, better with, but. My boat engine, does not have plugs wired, still starts 1st go.
More explaination required.
SD
November 2011