Technically, modifications don't void your warranty. As Vig points out, US legislation prohibits manufacturers from voiding warranties or requiring only factory parts be used.

That said, if you modify the fuel system (or intake system) then you should expect that future problems in that system will be assumed by the dealer to be due to your modification (guilty until proven innocent). It may not seem fair to you, but it is often true that problems are due to modifications more so than to defective OEM components. Also, problems caused directly by your modification are obviously your responsibility. That extends to things like wide tires wearing suspension components faster, or aftermarket phones making the battery go flat.

The final point is that different dealers have different tolerances for your modifications. Some will not try and pin it on you, if the system impacted isn't one that you have modified. Others will be more of a pain. Your best defence is a good relationship with your dealer service advisor.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue