HELP- Constant Loss of power underload

[neil reid]

All,
Thanks for reading, new to this Forum.
I have a Yanmar 6 LPA-STZP Year 2004 in my Monterey 265. The problem i have is that whilst the boat is in idle and i rev it up, there is no issues at all. Everything runs and sounds good. No smoke, black or white. The issue arises when i go into gear and underload and apply revs. When it gets to about 2200/2500 rpm the rpm dies off to almost idling, then picks up again to the 2200/2500rpm. It will not pass this point. It feels like you are driving your car and it is almost out of fuel. The boat runs for a couple of seconds then slows down then speeds back to to max 2500rpm then back down again and so on and this is with the throttle full open. It will not go beyond this point as it just dies off. Max speed i can get is about 8knts before rpm slow down, where the boat normally runs at 30knots.
I have replaced fuel filters, air filters, fuel/water filters, oil filter and there is 200ltr fresh new fuel in the tank. Does anyone know what the issue could be. I have been told it could be the turbo but it sucks when idling at 2500 rpm. There is no play in the turbo. I have checked the lines and found no fuel leaks anywhere, . Would the pickup in my fuel tank possibly be partially blocked.
At my end with this one and if left to the mechanic i think he would end up replacing everything from turbo to fuel pump etc where it could be a simple problem.

This happened al of a sudden and was not a gradual issue.
Any help would be greatly appreciated from all you knowledgeable boater out there.

thks neil

 

[pandos]

I would guess fuel pump is either on the way out or you have a blockage somewhere.

Could also be a blockage in the tank breather. Or if there is a screen around the tank pick up pipe.

Try running it with the fuel cap loosened..

An easy test for the fuel pump would be to fit a 12v facet pump in the fuel line if this fixes things it's the pump...if not at least you have a way to bleed the system easily...

Might also be a lack of air into the engine., is there an air filter?.

 

[Jmc1764]

Also check your exhaust elbow, it could be getting clogged and causing a restriction, the engine will still run but under load it cant breathe properly and drop in power.

 

[neil reid]

Air filter has been changed out with OEM part. Even with the filter totally removed it still acted the same. I will remove the elbow this week to have a look along with pulling the fuel line out of the tank to check. Would the waste gate cause this issue. If it was not functioning properly would that mess with the turbo functioning properly and in return not allowing the turbo to suck enough air??

 

[RichardS]

Air filter has been changed out with OEM part. Even with the filter totally removed it still acted the same. I will remove the elbow this week to have a look along with pulling the fuel line out of the tank to check. Would the waste gate cause this issue. If it was not functioning properly would that mess with the turbo functioning properly and in return not allowing the turbo to suck enough air??

If the wastegate was not opening properly the boost pressure would be too high whereas you have a loss of power. This might be caused by a wastegate which is stuck open or not closing properly.

Definitely worth checking the exhaust for blockage.

Richard

 

[ianat182]

I think it might be worth checking your throttle linkage, cable may be sliding through the clamp or banjo bolt fitting ; as the engine revs the cable going back to the idle position through the clamp. Happened once on mine, simple clamping if teleflex ends .
ianat182

 

[neil reid]

If the wastegate was not opening properly the boost pressure would be too high whereas you have a loss of power. This might be caused by a wastegate which is stuck open or not closing properly.

Definitely worth checking the exhaust for blockage.

Richard

Thanks Richard. I will look into the exhaust this week. Thanks again for your reply and knowledge. Helps a newbie to boats like me understand things a little better.

 

[neil reid]

I think it might be worth checking your throttle linkage, cable may be sliding through the clamp or banjo bolt fitting ; as the engine revs the cable going back to the idle position through the clamp. Happened once on mine, simple clamping if teleflex ends .
ianat182

Thanks Ian. The engine without load can throttle up to max rpm suggesting no issue with the cable but I am certainly going to check this. I hope it is as simple as this. Fingers crossed. Thanks again for your reply. Greatly appreciated.

 

[jwfrary]

Sounds life fueling to me.

Insert a vaccum gauge in the line before the lift pump shouldn't produce more than about 4 psi vac at full load if the filters are clean.

Gunson G4103 - Lo Gauge Vacuum Tester - Machine Mart - Machine Mart

Exhaust hose is a good shout little sister as well as the elbow others have mentioned.

 

[LittleSister]

As well as the potential exhaust elbow issue, I have read of people having problems following an internal collapse of flexible exhaust hoses suddenly restricting exhaust flow.

 

[mrangry]

My Racor fuel water trap/filter was blocked and caused similar issues.

 

[neil reid]

Update.
Took the fuel hose off and found plugged tank side. Blew it out and working great. As mentioned usually a simple fix and there was me thinking turbos etc. Thanks all for replies

 

[pvb]

Update.
Took the fuel hose off and found plugged tank side. Blew it out and working great. As mentioned usually a simple fix and there was me thinking turbos etc. Thanks all for replies

Did you blow the muck into the tank? If so, it'll happen again.

 

[neil reid]

No it was in the line. Now u have me worried there may be more in the tank. The tank is not accessible, any ideas to clean out tank. Only small opening where fuel gets sucked out of

 

[burgundyben]

No it was in the line. Now u have me worried there may be more in the tank. The tank is not accessible, any ideas to clean out tank. Only small opening where fuel gets sucked out of

Fuel tank needs a decent size inspection hatch in the top.

 

[Arcady]

Fuel tank needs a decent size inspection hatch in the top.

Ideally yes, but even a small access point will admit a thin suction pipe on a Pela pump or similar which can be poked around to pick up crud from the bottom.

 

[CJU]

We had a simile problem over the years and eventually bit the bullet when it became apparent it wasn’t just one of those things. We had a tank cleaning cleaning company do the work and what he found after cutting an access hatch in the plastic tank was a piece of paper towel, which periodically wrapped itself around the pickup pipe filter, plus a bit of crud. So far the hatch has remained fuel tight.
According to the man finding stuff like paper towel in the tank is not uncommon ?

 

[Blueboatman]

These things really should be supplied with easy access inspection plates on the top - surprised there isn’t a best code of practise for new installs , given the prevalence of bio diesel and big issues ..
Or, easy removal of the whole tank itself , ha!

 

[Realbeerad]

All,
Thanks for reading, new to this Forum.
I have a Yanmar 6 LPA-STZP Year 2004 in my Monterey 265. The problem i have is that whilst the boat is in idle and i rev it up, there is no issues at all. Everything runs and sounds good. No smoke, black or white. The issue arises when i go into gear and underload and apply revs. When it gets to about 2200/2500 rpm the rpm dies off to almost idling, then picks up again to the 2200/2500rpm. It will not pass this point. It feels like you are driving your car and it is almost out of fuel. The boat runs for a couple of seconds then slows down then speeds back to to max 2500rpm then back down again and so on and this is with the throttle full open. It will not go beyond this point as it just dies off. Max speed i can get is about 8knts before rpm slow down, where the boat normally runs at 30knots.
I have replaced fuel filters, air filters, fuel/water filters, oil filter and there is 200ltr fresh new fuel in the tank. Does anyone know what the issue could be. I have been told it could be the turbo but it sucks when idling at 2500 rpm. There is no play in the turbo. I have checked the lines and found no fuel leaks anywhere, . Would the pickup in my fuel tank possibly be partially blocked.
At my end with this one and if left to the mechanic i think he would end up replacing everything from turbo to fuel pump etc where it could be a simple problem.

This happened al of a sudden and was not a gradual issue.
Any help would be greatly appreciated from all you knowledgeable boater out there.

thks neil

This is an older post, and I am glad it seems like you got to the bottom of your issue. For future searchers experiencing similar symptoms, this is not a turbo issue because mine is not a turbo model and is exhibiting the same symptoms. This is an issue that affects Yanmar engines in marine settings as well as ag/ lawn care settings. I’m only looking for answers from people who have been through this and found what the basics of diesel maintenance and repair and diesel technicians are not aware of. This is not a “basics” issue, it is a Yanmar issue. I don’t post public questions until I’ve covered all the basics and I do have some training and experience in diesel maintenance and repair. It does act like fuel starvation, but only happens in gear or when the hydrostatic transmission is engaged. Starts and runs fine and works for about an hour then sputters and stalls to around and below idle speed, blowing blue smoke while it runs with a stutter, rpms can’t be increased, and no work can be done at all or engine will die. May or may not re-start trouble free, once it happens it continues to happen. If it doesn’t start right up again like nothing happened, it will not start again and stay running until after it cools down. Everything is clean and clear and/ or new. Started out of the blue with no increasing issues or warnings leading up to this. To me it seems temperature dependent and related to the hydrostatic transmission.