The BMW M550i xDrive packs a twin-turbo V8 and all-wheel drive into a comfortable four-door car for outrageous performance. However, recent testing by Car and Driver revealed that the acceleration of the sedan wasn't quite up par. Thankfully, reports are in that BMW has looked into the issue, and the missing acceleration will be accounted for in a simple software update.
The issue became apparent when Car and Driver tested the M550i xDrive and found it could only deliver a best 0-60mph time of 4.1 seconds. Quick, to be sure, but not quite as quick as it should be. This became obvious in comparison with the BMW X5 M50i. The two vehicles share the same 523 horsepower twin-turbo V8 engine, but the hefty X5 SUV was delivering a quicker 0-60 of just 3.9 seconds, despite weighing a full 856 pounds more than the sedan.
Indeed, the result was also much slower than BMW's claimed result of 3.6 seconds, too. Early suspicions concerned the use of low-octane gasoline, but running fresh 93-octane fuel only shaved a further 0.2 seconds off the time.
BMW investigated the results, eventually uncovering the culprit. A software issue meant that the stability control system was intervening on hard launches. From a standing start, the system would command a boost cut, lowering the available power from the engine and thus leading to the slower-than-expected 0-60 times.
Rectifying the issue simply requires a software update, which BMW will be providing over-the-air or via its service departments. Car and Driver have since tested an updated model, which delivered a 0-60 mph time of just 3.5 seconds, carrying on to a quarter-mile in 11.8 seconds at 119 mph. Quicker than the stated figures, it seems to be ample confirmation that the problem has indeed been fixed.
It's a curious thing to happen in a production vehicle. It perhaps suggests that minor changes may have been made to the stability control system after BMW engineers took their official 0-60 measurements. Regardless, the issue has now been fixed, and M550i owners will no longer be embarrassed by losing to Ferrari F50s at the stoplight drags.
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