Update-high pressure pump

[Cobia270]

So the mechanic finally came and reinstalled my high pressure pump. Took it out ran great hit the high rpms. On the way back to the dock as soon as I hit the 5mph zone the engine seemed like it wanted to stall. Turned around opened it up ran great but as soon as I slowed down to less than 1300 rpms the engine started sputtering. What do you guys think? Is it possible I fouled a plug or two?

[rodbolt17]

no, I still think you have a lift pump/check valve issue.

[Cobia270]

2 new lift pumps installed. The engine didn't sputter on the way out. But after opening it up for a run it began to sputter at idle and 5 mph .as soon as I gave it throttle it ran fine. I called the mechanic back and he told me to check plugs before he charges me to comeback.

[greasyshaft]

Would make it a lot easier for others to help if you just updated original thread

[Cobia270]

Would make it a lot easier for others to help if you just updated original thread

2001 200 hpdi's . Put the boat in water after long winter. Did water pumps, canister filter, water separator, fuel filter, new vst filter, new lp pumps, new plugs. First run couldn't get the boat over 3500 rpms. Mechanic came with laptop and found high pressure pump dropping to less than 500 at full throttle. Was gonna send the pump out but I changed the filters myself. Mechanic put the pump back on. He never bay tested it after he reinstalled the pump. Today I took it out. From the dock at 5mph it ran fine. I got it to open water and I got it up to 5000 rpms.boat ran great. On the way back to dock as soon as I hit the 5 mph zone the engine started to sputter like it wanted to stall. I turned around to see if I could open it up again which I could but as soon as I backed it down to 5 mph it happened again.

[Cobia270]

Any ideas?

[99yam40]

If check valve , maybe you can find a way to test

[rodbolt17]

have you actually tested the lift pumps for leakage?
what is the medium pressure when it fails? what is the HP rail pressure when it fails?
have you done a simple Kv test on the plugs when it fails.
Kv test needs to be made in gear.
TPS voltage needs to be set using the correct procedure.

[Cobia270]

Today I pulled the plugs checked them and reinstalled them. They looked new. When I went to start the boat I had the same issue . Engine wanted to stall. When I tried to rev it in neutral nothing. Tomorrow I'm gonna change the lift pumps even though they have 0 hours on them. The only other thing I noticed was that the reserve oil tank on the engine was full to the top. Related?

[99yam40]

You need to be testing things not throwing parts at it

[rodbolt17]

you do realize in N below about 1500 its only running on 4 cylinders.
above about 1500 and its only running on two cylinders.

[Cobia270]

Replaced the lift pumps today, checked vst filter again, put a new canister filter on , changed plugs and now the engine starts up and immediately stalls. Also put in a gauge on the vst valve and was getting 50psi. And to top it off Yamaha mechanic not returning calls

[Cobia270]

Will the yds be able to tell anything without the engine being able to stay running?

[greasyshaft]

yds will work when the key is in the on position

[Cobia270]

Machanic came down to boat today hooked up laptop and now I'm only getting 150 pounds out of the high pressure pump. Went from 500 before I changed the filters to 150 after the new filters were installed. I don't get it. Off it goes to flagship marine.