Hi chaps. Just bought a 1991 2.4 5 cylinder diesel and it takes a lot of cranks before it fires up. There is also a very faint smell of diesel. Watching the clear diesel supply line we can see lots of air inside the pipe. I know these systems should self blieed so I am assuming there is an air leak somewhere. However when the engine is turned off you can see the diesel flowing backwards in the supply line back to the filter. Is this the cause of the prolonged starting as its taking time to push diesel to the pump and is this just caused by the air leak? Or is it normal to flow backwards when the engines off? Or is it missing a non return valve or something? The pipe routing is pretty shody so its obviously been played with by the previous owner.