Working on a 175 HPDI Yamaha. When I run the diagnostic fuel pressure flashes orange and shows low pressure. Gauge hooked to VST shows 50psi steady at idle and load. Motor does not want to go above 2000 rpms and surges boat will not go on plane but runs great below 2000 rpms like its in slow mode but no alarm sounds. When motor is cold it will sometimes go on plane and pressure will read 4.5 low and around 625 high side. My question is what does the fuel sensor control on this motor? Can it trigger slow mode and what effects does it have on the ECM as far a running goes?

We did take the fuel pressure sensor off in an attempt to clean it and the contacts. Now boat planes all the time but has a miss through all rpms. There appeared to be a green dust substance on the plug contacts. Thinking sensor may be bad, would it cause running problems if it is not working properly?

Also how does the diagnostic program get the low pressure reading as I don't see a low pressure sensor?

Also at idle diagnostic shows NO fuel pressure at idle, it will not show pressure until throttle is applied.