Google "Mercedes Benz M271 engine problems". There's also info about that engine on Pelican. I'm sure someone else more knowledgeable than me will chime in, but seems to me I recall reading that MB had so many problems with that engine they only used it ??2003 to 2005??.....and then stopped using it.

Apologies for not having a specific answer to the problem with your friends engine, but you might find the solution in the numerous posts on all the mercedes forums, if you don't find it here. Good luck.

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'89 260e (212K Mi.), '92 400e (208K Mi.), '92 400e (not a misprint) (146K Mi.), '95 C220, '81 240D--Sold