Lots of possible causes - is there any smoke from your exhaust when you're driving under normal circumstances? What about when you deck the pedal to accelerate?
Start with the easiest and cheapest things:
Swap your fuel filter, don't buy ****part, complete and utter ####ing bollocks. I've had one disintegrate in my old 90 in the past - filled the inlet banjo on the injection pump with mush and got inside the pump.
Crack the 8mm bleed bolt on top of the fuel filter housing and start the engine. Do you get fuel surging out? If not, lift pump is knackered and will not be supplying the injection pump with an adequate supply of diesel for harder engine work. There might be a few bubbles of air that come out too, this is quite normal but there should not be a continuous stream of bubbles. Air in the fuel at this point would suggest a leak in the fuel line from the tank and this will cause performance problems. It'll also show as white smoke from the exhaust (usually more obvious from a first start) and you might notice it takes a few turns of your engine before it fires up after being stood.
Check boost pipes between the turbo outlet and the inlet manifold (there's only two). They can delaminate internally and are sucked flat as the engine draws air in. It's got to suck before the turbo blows remember.
Check the turbo waste gate isn't stuck partially / completely open. A pair of mole grips on the actuator arm from underneath rocked back and forward should give you a good indication as to whether or not it's working properly. When it seats back in its resting place it should have a good firm stop as metal meets metal, not a soft / tight close.
Check boost pressure pipe from turbo to injection pump for splits / cracks. The injection system relies on a pressurised feed from the turbo to increase the fuelling as boost increases. You might also want to take the top off your aneroid chamber (top plate on injection pump with four flat head screws holding it in place) and check that the fuel pin moves freely. Make a note of the punch mark on the diaphragm, rotate the diaphragm through a full 360 degrees (either direction) and pull it out of the recess being careful not to loose the spring or the plastic shim. Find a small flat head screw driver and place it down the recess. Look down the recess and start the engine. A black pin should move out towards the back of the injection pump from the front as you rev the engine. If not - it'll be gummed up. Filling the recess with penetrating oil and then running the engine might free it off - will require a strip down if not.
Failing that, come back here! Should give you a few things to work with!
-Tom
