I remember the fellow in the below post seeming to have a good understanding of the fuel path. Scroll down toward the bottom. Was concerning a 96 but should be appreciably the same as the 98/99.

1996 Mercedes E300 ifi Electrohydraulic shut-off

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)