My '86 F350 has a 6.9L international non-aspirated diesel engine.Theengine cranks at a good speed but will not turn over. What could the problem be and where do i start?

 

Won't start at all,, or hard to start on initial startup?

Just quit, or became harder to start over time?

First, you need to make sure there's fuel/pressure at the fuel filter/schrader valve.. That the fuel lift pump is working and supplying fuel to the filter assy. Second would be to crank the engine and 'crack' loose one of the injector hard lines to see if the injection pump is supplying fuel out to the injectors.. You should see a pretty good 'spit' of fuel as the engines cranked over.. Injection pump failures are common with the older diesels.. A lift pump problem may starve the injection pumpfor fuel, or either can aerate the fuel causing a no start.. Glow plug/system failures (fairly common) can cause a hard start condition when cold, but generally will start with some extended crank times..