Yamaha VMAX 250 HPDI problems help needed!!

[Marsipulami]

I have a Yamaha VMAX 250 HPDI of 2003 year model. I have had the motor for about a year and last summer it was working excellent. This year I have started to experience some problems. It started out with the engine not running clean after starting and it even stopped. Then it escalated to loosing RPMs whilts running it for instance I can go at 3800 rpm and then it droppes to 3300 rpm and then goes back up again. It seems to be better after the engine becoming warm but it is not working 100% then either. I have taken it to the dealer and we discovered that the updates the Yamaha recommends has not been done so we will start with applying does. We ran a diagnostics and it showed that the proble discovered was low fuel pressure. All filters are regularly changed and the fuel is clean. Anyone who has any ideas about this?

Regards Marsipulami

 

[yamamarinetech40]

Re: Yamaha VMAX 250 HPDI problems help needed!!

I would start any fuel relating problem solving with a vacuum test in front(before) filter on engine unless something else just screamed at me....should be under 2" at idle, never more than 4.5" WOT....if the pump is starving for fuel it can't pump...or if you'd rather, use a portable tank with a good hose/bulb and run engine that way....a lot of boats in saltwater/humid conditions get just the tiniest bit of corrosion on anti-syphon valve's little ball that's inside and it sticks....I would punch that out(ball).....if it sticks you get high vacuum that can starve or put bubbles in fuel line...yes vacuum very high causes bubbles....

 

[rodbolt]

Re: Yamaha VMAX 250 HPDI problems help needed!!

I would start by cleaning the VST,replacing the medium pressure inline filter using the CORRECT clamps. then run the engine with the laptop and a medium pressure test guage as well as the vacum guage installed at the lower lift pump inlet. on that engine yamaha says you can have as much as 6"Hg I like 4"Hg or less. I wont punch the ball out of a safty device on general principle.
I will replace them with a valve of the correct head pressure rating though.
the low pressure pumps on the 3.1 and 3.3 motors take a beating and I reccomend simply replacing them about every 3 years.
but keep runnning it lean and you will see how expensive it can get.