I'm almost certain your 190 does not have a 21 gallon tank. The 300E tank is only 18.5 gallons, the 190E must be smaller than that. The W124 diesel had a 23 gallon tank.

Sounds like a clogged filter to me.

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...