Quote:
Originally Posted by Andruha
I have X5 35d with just 1,300 miles on odometer. During break in period I was quite gentle with acceleration. 2 days ago I decided to try accelerating a bit harder and noticed that between 2,500 and 3,000 RPM engine makes knocking sound that reminds me valve knocking on older cars. After 3,000 RPM it goes away. On park there is no knocking sound and engine runs smoothly at any rpm. Is it possible I got bad diesel at a gas station? Has anyone with a diesel experienced the same? Just a thought of something being wrong in a new, 1 month old car is driving me crazy  TIA |
In my opinion, there shouldn't be any difference in sound. Of course, heavy acceleration will sound louder, but you shouldn't hear knocking. What makes you think it sounds like valves? Is it light tapping or knocking?
Did you notice this after a fill up? The US has sketchy diesel fuel at discount stores and it could be poor fuel. It could also be water in the fuel, but BMW has pretty good sensors that will warn you of water in the system. Water will trash our injectors and will stop your engine, if there is enough water. The fuel timing (when fuel is injected during the compression stroke measured in degrees prior to top dead center - TDC) on diesel injection, if your fuel is bad, can make the engine sound like there is a tapping at certain RPM. Under heavy load, the tapping can get louder as the ECU adjusts/increases the timing to meet the new input requirements.
I don't think it could be tranny related as you checked the sport mode and there is no difference. Sport mode adjusts the engine's tune, but more importantly, it also adjusts the shift points and locks the torque converter earlier. This gives you improved throttle response and shifts the tranny in the sweet spot of the engine's power band (to prove this, press the sport button at 40mph and watch the tranny down-shift which increases the RPM to the be in the peak torque range).
Anyway, if you don't think it is fuel related, you need to have the dealer check this out as the engine should be consistently smooth and relatively quiet. Under load, it will be a bit louder, but consistently so through the RPM's.