its a L322 with BMW diesel engine, the vehicle runs ok generally accept it looses power , drops down to around 1000 rpm and then starts to recover . he has replaced the filter under the bonnet and the maf but it still dose it . he thinks it could be one off the 3 pumps that it has (which sounds very possible). its a random thing that happens on occasion but is getting worse . is this a thing that happens to these or is it an unknown issue,
PS i have never owned or worked on diesels so its all foreign to me ,any info would be very appreciated, thanks

I am not that familiar with the L322 but the M57 engine is the next evolution of the M51 engine in the p38.

First rule out the turbo hose being split. Examine closely and, with the engine running, run the palm of your hand close to the hose and the inlet manifold to feel for any leaks. Usually it would be accompanied by a smokey exhaust. I have had hose splits that seal up and difficult to see. The hose can also delaminate inside. Hard to detect without taking the hoses off.

Next is fuel. Any bubbles in the line to the FIP? Not even sure it has a clear pipe like the p38. Fuel filter has been changed?
Dirty diesel? run some off the bottom of the filter into a jug and have a look see.
Disconnect the MAF completely. It will revert to default settings if it is like the p38.
Intank fuel pump gone? What are the 3 pumps? FIP is one, intank pump is two, what is the third? Excuse my L322 ignorance.

hi dave thanks for the reply , i will look into the things you mention ,also he replaced the turbo pipe as it was damaged but i will still look into it . he mentioned that their was 3 pumps so i went with it , will clarify when i ask him? yes it dose have the clear fuel line and he did mention that it was something to look at . he has some type of diagnostics and i offered to drive around and look and watch the graphs etc , will report back when i see him again.
thanks.

hi dave spoke with dale about his issue , he has replaced the intank pump but it did not fix the problem . asked about the 3rd pump apparently there is a intank pump an external pump outside the tank and the main pressure pump?have looked for leaks but did not find anything. he is using SCOPE as his diagnostics (i think thats what it was called) runs through a dongle to a phone app, appeared to work ok. just a side note i think i heard it miss a couple of times but this could have been the ac kicking in but it didnt sound right ?

The sound of it missing a few times is a clue I think. Maybe one of the injectors isn't running right?
The engine is direct injection, unlike the p38 diesel, which is indirect and just a simple pintle valve.
It could of course be something else, but if your friend has done the checks I recommended and come up with nothing, I would move on to other things to check out. I would next take the injectors off and get them tested. Find a commercial diesel garage with the testing gear. It shouldn't cost too much and they will clean the nozzles and replace seals.

just to bring this to an end , i was speaking to person the other day and he stated that it was the actual turbo was the issue. after replacing lots of things he had someone offered to do diagnostics on it as training for their apprentices . after lots of teachings they found the turbo wasn't communicating properly, the turbo was leaking oil into the manifold which over time carboned up and stopped it reading correctly as it has a progressive gate , it would over boost then have nothing as it wasn't reading correctly . replaced turbo and all is good again .