This is so strange - my dad and I own this boat and he knows a lot about engines, and we're both stuck. We have had all the injectors testing and the high pressure pump and all are good. We've isolated different areas and still nothing has worked.

We can start the engine by one of us continually pumping the manual primer pump, if they keep pumping it will stay on in idle, but soon as they stop the engine stalls. However, if we put the revs up to 1400 then she runs beautifully and has no issues, then we drop it to 1200 and she hunts up to around 1300 and down again. Then if we drop her below 1000rpm she stalls. Does anyone have any idea how this works? Changed the Racor filer, tried running it directly from a bucket of diesel, and can't see any obvious leaks anywhere.

Any advice would be super helpful! Thanks