200 TDi Sluggish

I'm starting to wander if the low boost could be caused by a fuelling problem. As I understand it, turbo boost depends on the heat of the exhaust gasses, which will be less if there is insufficient fuel going into the cylinders. I'd double check that the fuel lift pump is able to deliver a sufficient flow of fuel, by pulling the inlet pipe off the injector pump and cranking the engine over. Another possiblility is that the mechanism in the fuel pump for matching fuelling with boost pressure is not working. You could test to see if this mechanism is working, by disconnecting the small pipe from the turbo to the fuel injection pump, and sealing the outlet to this pipe from the turbo. If the vehicle drives just the same as before then it points to a problem in the injector pump. I think you're getting to the stage with this problem, where contacting a proper diesel engine specialist would be a good move.

Thanks fenby - appreciate the advice.
I think though the boost depends on the FLOW of exhaust gases, not the heat. As it's revving fine, it's therefore generating the correct flow of gas, but it's just not spinning the turbo fast enough to generate necessary boost at the inlet air side.
Either that or there's a leak somewhere between turbo and inlet manifold (which has been suggested in this thread)
Either way I think I need to check the turbo itself - as Dr P suggested may be a broken vane on the turbine itself, or a faulty wastegate preventing necessary boost build up...
I'll try disconnecting the small pipe and see what difference it makes.
Lift pump is brand new so 'should' be OK - will check though...
After that I thing you're maybe right - a diesel specialist may have to be called in....

cheese_aholic said:

I think though the boost depends on the FLOW of exhaust gases, not the heat. As it's revving fine, it's therefore generating the correct flow of gas, but it's just not spinning the turbo fast enough to generate necessary boost at the inlet air side

Click to expand...

That's what I'd always thought about turbos, but a while ago I read that a turbo essentially extracts heat energy from the exhaust gasses and uses that energy to force more air into the engine. That's why you have to put the engine under load to generate full boost - the boost is not just related directly to engine RPM. You might find this interesting:

TurboClub.com Turbo-charger Fundamental operating principles Technical Information on Modifications for JDM Imports index

Cheers Fenby,
Indeed, very interesting (if a little technical!!)
I keep thinking through the fuel comment; surely if it's a fuel issue (i.e. wrong mixture / starvation / etc) then I'd be seeing some other issues such as smoke, or rough running / juddering under power?
I'll have a proper read through that link and see what I can ascertain...

Under fuelling should not cause smoke - you get that with over fuelling. I don't think you'd get necessarily get juddering or rough running either. If your driving along at high revs and take your foot off the accelerator a diesel engine should not run roughly, and what is happening when you do that is the fuel supply to the cylinders is almost shut off. The speed of a diesel engine under a given load is determined by the rate at which fuel is injected into the cylinders.