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2000 150 hp OPTI DFI - 3000 rpm Sputter

L

l_nemes

New member

I have twin 150 DFI's and have recently had an issue on the starboard motor. I was cruising at 4000 rpm for maybe 15 minutes and it started to spatter/sputter so I then backed it down to 3000 rpm and it was fine. Until the fog and heavy seas rolled in it started to act up again. So I turned my electric fuel pump (that I installed to replace the ball) and the issue went away. Another 15-20 minutes and back it came. I can run at about 2500 or lower RPM and it will run fine and steady with no issues, other than running hot. I kept the boat at the dock overnight and changed the plugs. The next day it ran fine for another 15 minutes and the issue came back again. Could this be a faulty mechanical fuel pump? What all would you suspect it be?
 
Hmmm, computer controlled, sensor driven, multi-fuel pump, multi-injector motor that has to keep a 10 psi difference between gas and air in the rails after the gas has been vapour separated and the excess fuel is water cooled before it's recycled has a "stutter" and runs hot at mid rpms.

Not trying to be ignorant here, just trying to point out that your first bit of troubleshooting should be to have the motor plugged into a DDT and see what it spits out, then take it from there.

The Opti's more closely resemble the space shuttle than a traditional 2 stroke motor - you don't go at them with a screw driver and an ohm meter - at least until "after" the computer has told you what is wrong with them...
 
Had it to the mechanic, no codes nor any alarms going off. Not an electrical issue he said.

Changed the mechanical fuel pump, changed the plugs and still the same thing. After running at 3000 RPM's it starts to sputter and bog down under a load. Not under a load, it runs fine.

I know these are very ornery motors and require special attention. Next time out I will try to check the air and fuel pressure. Any other suggestions since I am not getting a code from the computer?
 
You have to put a gauge on the fuel rail to read the fuel PSI verses air psi (10psi difference) during failure mode......I suspect it is probably the high psi pump in the VST going bad......ethanol loves them!
 
Hooked up my gauge on the water side and wasn't seeing any pressure so i went to the fitting, well i tripped over my hose and broke the fitting and the engine died. Replaced the fitting and it started right up, idle and ran fine. Since i had a spare fuel rail sitting in the closet, i went ahead and swapped it out, just to make sure it was not the diaphram. And it was not, still sputter after 3000 RPM's. I ran Sea Foam and the ethonal sta-bil in for about an hour, i seemed that it became more alive at the 3000 rpm, and when i got to 3500 rpm, well sputter again. So i tried it in reverse at 3000 rpm and it did not sputter. Guess it is a lesser of a load and that is why it didn't.

Saw an VST online and since that is the only thing left to check. Not sure what else. Any other suggestions?
 
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