We have a customer at my boatyard who has a 2003 Pursuit with twin OX66 250's, and when she got launched last month she would not turn up over 2200 reliably.
Sometimes she would run OK up to 4600 RPM's and then fall on her face, other times she just wouldn't get up and go.
Only on one motor, other ran fine.
We did all the usual stuff, checked the fuel pumps (low and hi pressure) cleaned the VST tank, cleaned the O2 sensor, etc. etc.
Nothing helped. Eventually we sent out the injectors for cleaning and that fixed it right up.
Sea trialed her today, and she ran like a champ. Well, until I spun a hub. Doh!
Heres where we send our injectors for cleaning. Super fast and reasonably priced. Located in Bow NH.
https://www.dieselsfuelinjection.com/
FYI-OX66 Injectors are kind of a pain to remove though.