This BMW 535d, with a 3.0-litre diesel engine and two turbochargers, arrived with a tune from another workshop. Heavy black smoke came from the exhaust during hard acceleration, significantly reducing visibility for traffic behind. The existing ECU calibration and vehicle setup were inspected.

The engine control unit file was revised after the inspection. The main aim was to reduce excessive smoke while retaining usable engine performance. The case illustrates why tuning should consider more than peak figures: fuel delivery and exhaust smoke under load matter as well.

The video title describes the file as dyno-tested, but the final power or smoke readings after the revision are not clearly stated. No exact result is included here.