[jhbodle]

Accelerating hard out of a junction this morning, I realised that the other car coming down the hill was travelling far faster than I thought and had to plant the accelerator on the floor. Ran the car up to redline then shifted into 2nd and floored it again - only to find that there was no power whatsoever. It was like the accelerator pedal had been disabled. Revs fell back to idle and I coasted to a stop in the middle of the road. Put the car back in first and pulled away.

This has happened a few times now - always shifting from redline in 1st to 2nd gear. Has anyone else had this problem? The engine always lets me down when I need it the most.

[Bob UK]

Sounds like it has gone into limp mode for some reason and hitting the redline you have gone beyond the power band in a Diesel and it would have been slowing by the time you changed up.

That's just an observation due to everything in your garage being petrol before the 125d with peak power being 4400 rpm and iirc the redline is marked at about 5500 rpm I'd suggest hitting that regularly is going to cause issues.

[Bradbury]

Maybe it was the DSC that cut the power? If so, then I suppose the cure is to run it in Sport+.

[Bob UK]

Originally Posted by Bradbury

Maybe it was the DSC that cut the power? If so, then I suppose the cure is to run it in Sport+.

DSC wouldn't cut the power to an idle though.

[jhbodle]

I never usually take the revs beyond about 4500rpm, but I deliberately ran it to red line today and above 5000rpm the power is cut dramatically. You can really feel the drop off in power. I'm starting to wonder if it is cutting power to protect the engine at redline and not restoring it again once I have changed gear.

I doubt I can go to the dealer about it though. "Hey - when I shift gears at redline..." probably wouldn't go down well.

[ovekvam]

Why not? If the engine speed wasn't safe to use, BMW would have reduced the rev limiter further. You are supposed to be able to use the entire RPM range for acceleration, but you are not supposed to stay at the limiter for a long time. A few seconds will not harm the engine.

I remember we had a previous generation 123d at a track event. When pushed, it got a bit too warm. The engine management dealt with that by simply stopping the engine. The car had to be driven in the taller gears on the track to avoid this issue.

[Jeans]

Correct me if I'm wrong but are you really able to limit revs in a diesel engine as you would a petrol engine? Obviously you don't have any spark plugs to cut power to so I guess the only way is to cut fuel.
To me it seems as if there is no distinct rev limit, as there would be in a petrol engine, but rather just a gradual decrease in power. This is speculative, but perhaps there is a risk that the engine keeps revving when you declutch? Since there is no more effective way than fuel cut to limit revs?

I'm am however sure the combination diesel, 1st gear, full throttle, top revs does not sit well with me. There's 450 nm available some time before you hit the red. Perhaps this is just our ever so clever german friends teaching us how to handle their offspring

[ovekvam]

The petrol engines cut the fuel as well at the rev limiter. With direct injection, the engine will not keep revving when the diesel supply has been cut, even when declutched.