Nothing ! The dual pump set-up can be found in the 4-cyl as well. All you have to do is swap it out. The harness unhooks under the rear seat =)

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1994 E500 (MY SUNDAY DRIVER)
1993 190E SPORTLINE LE W/ M104 SWAP
1997 C230
2002 ML320
2000 BMW 528I (WIFEY'S CAR)

"Excuses are crutches for the unfounded."