I have a 1998 peugeot 406 2ltr turbo it runs fine except it does not have much power when in 3rd or 4th gear,very sluggish COULD THE TURBO BE OUT.

Have you checked the PCV system?? If its stuck in the closed position then you will lack power and turbo boost. A vehicle needs 3 things to make it run proper; FUEL,FIRE and AIR. Try that and see if it helps.

metal in the box oil indicates bearing failure in the transmission
in effect there is no 4th gear as it is a direct coupling of the in and out put shafts so there is no side load on the counter shaft and no load on those bearings so that will explain the noise in all of the gears except 4th which is straight through
time to pull the box before a bearing comes apart and damages teeth on the gears

Hi have you checked al the intake hoses and hoses to and from the turbocharger? And it's also possible that the timing may be off has the timing belt been changed?

Check for air filter or exhaust restrictions

I think some air going into fuel system.Need to put some compressed air in fuel tank and check for leak.

Sound like you are looseing some boost from your turbo,check all your hoses from your turbo,if all of them are ok you may have a waste gate sticking, you need to check for movement there it only move very little but has alot to do with hp.Thanks And I hope this helps you

did you change your clutch when you changed your gearbox??? also check the clutch master cylinder.

One of the thin vacuum pipes must be torn and the minute you go into higher/full boost the ECU doesn't get the requested pressure from the turbo and to protect the tubo from overboosting it puts the car into limp mode, The limp mode only resets when you switch the car off and back on again.

Trace all the thin 6mm vacuum pipes and you will find your leak.

Sounds like the gate valve is stuck. This valve dumps excess pressure when the turbo makes it.

Hi, I have a 2.0HDI Expert which was doing the exact same thing as yours, blowing thick black smoke, sluggish and loss of power on gradients, a hissing sound and surging. I replaced the air flow meter but that didn't help. I was told to replace the turbo but a turbo expoert told me not to as it would blow white smoke if it was faulty. I was then told to replace the injectors but a diagnostic test showed them to be functioning fine. I was then told to look at the intercooler which had thick sludge at the lower left pipe. I replaced it today - Sunday 12th July and it is now driving like a new van. It now pulls me up gradients with ease in 4th and 5th instead of having to drop gear to get to the top. I got a replacement from Euro Car Parts for £147 inc VAT. To tell if this is your problem, look through the gaps in the lower section of the bumper at what looks like the radiator and look for sludge over the inside of the bumper and all over the pipe where it joins the back of the radiator (intercooler). Also open the bonnet and look down behind the grille for the same sludge. Hope this sorts it for you. Barry, Newtownards, Northern Ireland.