Thread: 300tdi Fuel Supply Issue

Hey,

I am under the impression that I have a fuel supply issue. I'll start at the start...

I was doing a regular service and when bleeding the fuel system after changing the filter I noticed that some of the aluminium thread that the bleed screw screws into was on the bolt... This obviously started letting air into the fuel system. Just to get me driving again I placed some thread tape around the bolt and screwed it back in. Since this the engine was very hard to start and when it did it required significant revving to get the engine running again. Once going it drives okay but seems a little underpowered at higher revs.

Since then I have replaced the entire fuel filter housing and the fuel filter again (as well as a new bleed screw) however I still have the same issue. Once the engine is running if I open the bleeder screw no fuel comes out and nothing comes out if I try to pump manually from the lift pump.

I am of the assumption that it may be the fuel lift pump however I'm not sure why it would have failed at the exact moment I changed the filter and damaged the fuel bleed screw...

I have a new Delphi lift pump and intend to replace it when I get home from work tomorrow. I also have a new fuel sedimenter on the way from Bearmach that I will install in place of the old one which I believe has been on the car for 420,000km.

If anyone has any opinions on what the issue may be as well as any advice from here I would love to hear it!

Thanks in advance!

Dave

Edit: I have done a lot of reading and watched a fair few videos over the past few weeks and am hopeful that my diagnosis is correct...

Originally Posted by Devans

Thanks everyone for your help, I appreciate it.

Dave, when you speak of over stoking the lift pump, is there something I should watch out for when I put the new one in to make sure it doesn’t happen again or is it just a common fault of this particular pump?

Cheers

happens on all of the pumps of that style,

lets say the max movement is 2 inches. normal travel when running on the engine cam with no restriction to flow is 1 inch and 3/4 of an inch with nominal minimal resistance (all lines primed, engine not cranking 0 pressure in the IP)

when you turn the engine over the pump strokes until the pressure holds the diaphragm, as the pressure drops the diaphragm moves back and the cam picks it up again. it gets to a balance point and only ever moves so far.

When you crack open a fuel line if the cam is holding the diaphragm out and you turn the engine over as theres no resistance the diphragm moves further until the arm hits the cam again. in this instance if the diaphragm has gotten settled and aged it just gives up and the pump stops working.

When you operate the hand primer its designed to travel even further for 2 reasons.
1. it takes less pumps to prime the filter
2. if you happen to stop with the cam in the full lift position you can still get some movement to allow you to prime.

the extra travel puts even more stress on the diaphragm.



The arm being longer overall doesnt really matter so long as the bend and running positions are the same. the extra length just means it picks up earlier and strokes slower.