TSD

No (and Yes!) It is making boost all the time, but that's not because of the autobox setup. It's because some idiot designed it that way (or far more likely, some accountant made him do it) There were apparently a lot of TGV engines used in stationary generator applications, that may even be where the VNT version originates. In that application it might be perfect (or perfectly acceptable), I can imagine it's possible to set it up with a massive torque backup to stabilise the generator under load.

No, as said at the top of this thread, it's on boost all the time, because it's a VNT with a simple minded controller. It uses boost pressure to control the VNT mechanically, but I suspect there isn't a straight relationship between the VNT 'angle' and the output of the turbo, so it is only ever 'right' at one point (or very close to it). My TGV will produce boost while parking. In motorway cruise it will indicate around 15psi and 20 at full throttle. Mash the pedal in the midrange and it will spike higher. So much so that I can't be specific about the boost numbers because after 200k+ miles it has actually bent the needle on the VDO and it now permanently indicates a few psi of vacuum with the engine off

One question I probably should have asked - is this a real TGV, or one of the 300tdi conversions? I'm not sure its relevant to the problem, but there are some differences.

If it's starving for fuel at high throttle demand, and someone has tried to get the performance back by upping the baseline fuelling, then it could be the case that cruise fuel is too high, but not yet hitting the smoke limit, but there isn't enough left to give it some real top end grunt. That's sort of what led me to thinking of the FIP intake regulator. Every time miketomcat uses my Ibex, I end up quizzing him about the performance and handling, because I've owned it so long, and driven it so far, that I'm not sure I can tell if it's 'right' any more. It is, I'm sure, well down on power from when it was new, but probably not as down as I suspect on the days when it 'feels' slow.

You are assuming the TGV block has a boss machined with a deck height to take a Tdi lift pump, and that the cam has the same base circle to drive it. (The engine wasn't built with a LR pump from the factory, just a similar looking one.) I don't know and I didn't care enough to find out - I tried a couple of pumps and things got better but not fixed, so I just fitted a Facet as an experiment. Everything got better instantly, so I left it there. The lift pump 'should' only be an supplement to the lift pump internal to the FIP anyway. Which reminds me that it's worth checking the pressure regulator in the FIP isn't stuck - I had one that was stuck solid on one pump. Could give some odd results if it were sticking part-way?

I don't have the pump number to hand, but I can find it at some point. It is certainly different (as you'd expect) as International have different part numbers for the pump for the 2.5 (with regular turbo) and the 2.8 (with VNT). Worth noting that fitting a boost ring will be probably be a bit more involved than on a Tdi. The pump is mounted vertically on the TGV, so I imagine it would have to be removed from the timing chest to get access.

There's a few decent articles on the web explaining how the pump works, but the Bosch training manuals are a good starting point. BOSCH_VE_PUMPS.pdf TGV will always be at or close to maximum boost if you're on the throttle at all. It's an effect of strapping a VNT to a simple mechanical control system. It really needs electronic control (or a much more complex mechanical system) to get all the benefits of the VNT. I looked into it in detail when I installed my TGV, but that was a lot of years and miles ago, so I freely admit I'll struggle to put much hard science behind that statement! This has consequences - in light throttle cruise the pumping losses are increased (because it's always on boost) so cruise fuel economy must be slightly worse than the same engine with a conventional turbo. Also, when you turn the boost pin, the effect is less noticeable on the road, because constant boost means the diaphragm and boost pin don't really move. The extra fuelling is there, but because it's there all the time you don't feel it coming on in the same way. I suspect that, at cruise, the extra fuel from tweaking the boost pin just means you come off the throttle a little more, and end up pretty much burning same amount of fuel for the same amount of power. There are other adjustments that can add power and torque, but that's outside my experience. One of @vulcan bombers 'boost' rings might be interesting to try - I've not heard of anyone fitting one of thise to a TGV up to now. If you are loosing speed on long hills, and the EGT looks 'not too bad', then I would have a long hard look at the lift pump if you haven't already. When the original factory pump started to fail, I couldn't find a TDi pump that could keep up, and the Ibex really struggled to get over 70 on the flat. I fitted a low pressure electric pump and instantly top speed returned to much more exciting numbers. From memory (and as I said, it was a looong time ago now) when I put the TGV in, fuel economy stayed about the same as the tdi I took out. I was driving a lot of miles then, but there was very little motorway cruise, so I might well not have noticed a change in cruise economy. I think these days I probably get around 28mpg with much more cruising, if that's any comparison for you (SWB Ibex, on 33" with Roverdrive).

Just remembered something from when I had a cracked head... When I parked overnight I released the pressure from the cooling system. That reduced or stopped coolant being pushed where it shouldn't go, and the engine started sweetly in the morning. That was my final diagnostic before pulling the head, since head gaskets for the TGV are a bit more spendy than for a 300TDi.

It occurred to me you might see how much condensation the exhaust produces on a bit of glass or metal? Normally I'd imagine that varies too much from day to day to be any sort of guide, but you have an identical engine in the same place you can try at the same time. Just a random idea, might be a complete waste of time (like many of my ideas), but would only take 5 minutes to try.

Try cranking it first with the injector pipes loosened, to make sure the fuel system is fully primed? If there's some sort of micro-leak draining the fuel, that should at least make it clear itself noticeably quicker. That probably wouldn't account for the grey smoke though. Is it smoke or steam? (I have always found it hard to be sure.) Compression tester is here if you want it.

Help is clearly needed...

Couldn't remember, so back to the big box of invoices... 8L of Etch Primer 3L of high build primer 10L of 2K Acrylic (YELLOW 😎) And that was more than enough of everything, to paint a LWB and a SWB, plus the fridge, my watch, phone, and in fact most of the workshop I think there was about 2.5L of topcoat left over, the only thing we ran short of was the HB primer. For some reason I only ordered a 1.5L can, so had to get another before we attacked the second truck a week later.

I'm aware of the YBE100540 sensor, and that electrically it's different to the more common YBE100530. I'm curious to know what gear fits the end of it, since the 'speedo gear' question pops up every now and again.

Every day a schoolday! Never seen one of those, any idea for a part number?

If I remember correctly, when you go to larger tyres than the standard 32", you move off the end of the range of available gears. So of the available gears, Blue is the nearest to correct. Of course, if all else fails, you can just fit whatever gear comes to hand, and reprogram the speedo to read correctly. Any chance a bit of the old speedo cable is stuck in the drive gear? I can't think why else it wouldn't fit, though I have found it a bit fiddly occasionally. As far as I've seen the speedo drive gears all have the same centre square.