Can anyone tell me why my 55td van has no pulling power?

is air filter ok, has fuel filter been changed, is it getting full throttle, is exhaust clear,is tank venting ok [is there a huge rush of air when fuel cap removed - there is normally a slight air rush ], check all fuel lines especially down back of engine -they rub through speedo cable/gearbox mount etc,check tank unit elbows for excess corrosion, there may be something in tank partially blocking outlet pipe? i would think timing is ok with you saying that it runs ok at times. [if there is a hand primer on filter head this could be faulty give it a good few pumps and see if it leaks,should go hard to press if ok]

k
January 2010