A follow up on the 190E 2.6 hard starting. The change in spark plugs did not help long, the car starting getting progressively hard to start over the next 3,000 miles till it almost would not start at all. After it started, engine would stumble when accelerating from a stop.

I followed the advise of you all, and did the following till it corrected the issue:

Checked fuses on OVP Both 10 amp fuses on to top of OVP OK
Changed the fuel accumulator. No improvement.
Changed the injectors. Slight improvement.
Changed Spark plugs Slight improvement.
Pulled the OVP off, open it up, re-soldered connections No improvement.
Replaced OVP, Big improvement!!!. Quick starts, no stumbling.

Thanks for the assistance and advice of this forum.