Tuning Problems: Troubleshooting & Solutions

Hello, fellow diesel enthusiasts!

I've often read through this forum and have already received some helpful information. Unfortunately, I haven't found anything online about my current problem. I know that this forum mainly focuses on VAG vehicles, but I appreciate the expert opinions here, which is why I hope that the fact that I own a BMW will be overlooked. My car is a 123d from 2008, which has the well-known N47 four-cylinder common-rail engine. Due to a timing chain failure, the engine was replaced by BMW in 2015, and it has now been driven almost 100,000 km. The injectors were also replaced at that time. As far as I know, the rest of the components are still from 2008. The total mileage of the car is almost 230,000 km.

Ich hoffe, dass das als Hintergrundinformation vorerst reicht, ansonsten bitte nochmals nachfragen. Kommen wir zu meinem aktuellen Problem. Ich habe vor kurzem eine Downpipe verbaut und einen größeren Ladeluftkühler (BMW Performance Parts; ca. 50% mehr Kühlleistung als der originale LLK). Anschließend wurde mein Motorsteuergerät optimiert und zudem der DPF und das AGR aus der ECU entfernt. Das Fahrzeug läuft an für sich gut, jedoch hatte ich direkt nach der Optimierung das Problem, dass der Motor auf der Autobahn beim Beschleunigen mit Vollgas bei ca. 180 km/h bei ca. 4000 Umdrehungen einfach ausging. Ich bin dann rechts ran gerollt und habe den Motor erneut gestartet. Nach 5-6 Sekunden drehendem Anlasser war der Motor dann wieder an. Das Fahrzeug fuhr dann auch vorerst normal. Ich habe dann probiert, ob dieses Problem auch in niedrigeren Gängen bei Vollgas vorkommt. Hier passiert es nämlich nicht. Lediglich bei Vollgas ab 80 km/h im dritten oder vierten Gang, geht der Motor ab 140 km/h in den Notlauf und reduziert die Leistung auf ein Minimum (Motor läuft wie ohne Turbo). Nach Neustart ist wieder alles in Ordnung, was ja aber nach einem Notlauf nichts ungewöhnliches ist. Bei normaler Fahrweise oder kurzem beschleunigen passiert nichts. Die Symptome hatte das Fahrzeug vor der Optimierung nie, egal wie sehr es gefordert wurde. Only during longer trips with full acceleration did the vehicle noticeably have less power.
A reputable tuner has taken over the engine tuning, and he has already optimized numerous 1-series models with N47 engines. According to his assessment, the high-pressure pump might be in poor condition, which could be the cause of these misfires. A friend of mine had a very similar problem, which was resolved after replacing the two pressure sensors.
After these diagnostic runs and the engine cutting out at full throttle, the error memory was clear.

Thank you to everyone who has read this far and might have an idea about which component might not be able to handle the increased power, or what other cause might be behind my problem. The pressure sensors are relatively inexpensive and easy to replace. Replacing the high-pressure pump is not a problem for me, although it is known to be somewhat more expensive. I am grateful for any advice!

Best regards, Ben.

If it's going into limp mode, read the error codes first, and then we can say more. It could be caused by many things, from excessive boost pressure to low fuel rail pressure, among other things.
Re-run the original dataset and see if the issue occurs again.
If not, then you have to adjust the tuning accordingly.

Thank you for your reply. The strange thing is that the error memory is empty. With the original software, it ran without a single problem.
Does a high-pressure pump wear out in a way that, at the end of its lifespan, it can no longer deliver its full performance or more than its original performance? If it is indeed worn out to that extent, wouldn't it be better to replace it now, before it fails completely and distributes debris throughout the entire fuel system?

Ohha.

Before the "expert tuning," everything was fine. Afterwards, the engine unexpectedly shuts off without any error messages.
A hardware component is supposedly to blame.

I would suggest going back to the expert and having them drive the car while monitoring the relevant data (which is what the expert should be able to do). Everything else is nonsense.

Of course, you can replace the pump... or any other part...

Thank you very much for your reply. Your suggested solution makes sense, and I will observe the readings with the tuner when I have time.
Out of curiosity, I would like to know whether a high-pressure pump gradually wears out, resulting in a progressively lower maximum pressure, or whether it suddenly stops delivering pressure altogether.
Best regards, Ben.

Unfortunately, with the diagnostic tools I know, you can't really see much in a BMW. However, you can definitely check the turbocharger boost pressure and the fuel rail pressure.