97 W900 will turn over but wont start

What motor?

 

Take the fuel filter off and fill it up with diesel.. you are getting air somewhere.. If it starts and runs it justed needed primed if it starts and runs for 4 or 5 seconds you need to find where you are sucking air... When you start it (after filling fuel filter with diesel stand on the throttle as you crank it..

 

There should be a thinner wire that goes from the batteries to the ecm. Do you get any fault codes ? Make sure the batteries are fully charged. Does it sound like the motor is spinning fast enough when cranking it. Just make sure it's not a fuel issue, loosen the return line on the back of the head , and just make sure you get fuel to the injectors.