Anyone know about diesels ?

[2112]

The yoof at work has a BMW 530 diesel, it's the 6 cylinder diesel engine model. It ticks over OK, goes up the rev range OK but gets really rough in the midrange and then smooths out again. The fuelling has been checked and is spot on, the ECU is also fine. The fuel pump has also been checked out and is OK as are the injectors. So, it led me to think possibly compression ? The car has been checked for pretty much everything and has been on the 'official' BMW diagnostic computer and shows nothing wrong with the engine (it does show some issues with the air suspension).
He's just had a compression test done and has the following results -
Cylinder 1. 200.2
Cylinder 5. 200.0
Cylinder 3. 198.0
Cylinder 6. 204.2
Cylinder 2. 189.8
Cylinder 4. 196.6
For full disclosure I have no idea what the units are, but I would reckon them to be PSI ? The variation is only 14.4 (whatever units?) from 'best' to 'worse'. Could that be the issue? I know little about diesel engines other than they are heavy, dirty, slow and old fashioned. He has access to another engine which was running well before he put that car backwards through a fence... Any help appreciated.

[Upt North]

I ran a BMW diesel for a number of years and it did benefit from the odd couple of tanks of BP Ultimate and BMW's own fuel additive to clean things through.
Especially if he normally buys the cheapest crap he can find.
Worth a shot because changing that lump will be.......erm........horrible.
Mine also required an egr and turbo replacement which are common failings.
As he tried a BMW specialist rather than a main dealer?
Upt.

[2112]

As far as I'm aware he's using a BMW specialist in Washington. It has to run on the high quality diesel as it's been re-mapped. He's had it back to the place that mapped it and it all checks out OK. It's very odd, I'm starting to wonder if the crankshaft is slightly out of kilter?

[Rusty Nuts]

You'd think BMW diagnostics would pick up on a hall sensor being in the wrong place at the wrong time if that was the case, though?

[2112]

It's really odd, super smooth a tickover and by 3,000rpm it's rattling your fillings out and then it goes back to being smooth again. Most puzzling?

[Upt North]

Is this when the vehicle is stationary or moving. Or both?

[cooltshirt]

As upt North asks .......
Then I'd look at prop shaft and engine / transmission mounts.

[kwackboy]

Not a diesel expert but that sounds like a drive /prop shaft issue ..

[2112]

The condition is worse when static, much less noticeable on the move. The engine goes great, pulls like a train but has this horrible vibration starting at around 2,000rpm and it's gone by 3,500rpm. Weird. He's taking it to another garage today so fingers crossed they may find something?

[nigel s]

Ask the owner of this?

[Upt North]

I've got it, I've got it! Well maybe?
Harmonic Balancer on its way out. Easy to try if he's got the other engine?
Upt.

[2112]

A good call sir. I shall suggest this when I see him on Tuesday 

[purplebikeunicorn]

Engine mounts for definite. Don't know what BMW use but my old car used an oil filled mount - looked absolutely fine from the exterior but was doing bugger all damping (and when you took it off, you found the tell tale signs of oil dropping off the bottom of it).

[Hugo Magnus]

I wonder if the catalytic thingy is disintegrating and restricting flow?

[2112]

Long since removed... It only has the two back boxes as 'silencers' and they're not doing very well at it!

[2112]

So, the saga seems to have ended. After a trip to yet another garage on Saturday, water in the diesel was the diagnosis. Drain & flush the tank, new fuel filters, some fresh diesel in and it's running as sweet as a nut. The BMW onboard diagnostic sytem is not clever enough to spot this issue due to it's age (it's a 52 plate) as it's not that sophisticated. All's well that ends well etc.