6lpa-stp not getting full power

[special k]

so last season my 28te with yanmar 6lpa-stp one day wouldn't get above 3200rpm under way.
changed both fuel filters with no positive results. boat ran fine otherwise. comes up to 3200 smoothly and without smoke.

had bayside diesel from mystic ct service the engine this week doing a valve adjustment, oil change, heat x-changer and turbo wash. they also checked throttle cable throw. boat runs fine but still not getting above 3200. techs at bayside have no answers to my problem. perplexing!
boat has newly tuned prop, clean bottom, fresh fuel. they suggest maybe checking injectors with pop test and maybe new nozzles. with it coming up to 3200 smoothly and quickly i am reluctant to believe injectors are my issue and don't care to spend large dollars chasing ghosts. engine will get to 3900-4000 with no load.
at 3200 my speed is the same as it always was and no different weights or conditions on my boat.

i have an e-mail in to mack boring but have no reply yet......any thoughts out there??

[JackK]

Since the prop is the only change in the equation - Were there any changes to the pitch, cupping, etc on that prop. That would be my first place to look given that you aren't having any issues getting to 3200 RPM.
Next, Get a hold of a photo tach to make sure that is reading correctly. When my boat was new, the tach was not reading correctly. There are jumper settings on the back of the guage. Long shot, but could one of the switches changed?

Jack

[special k]

sorry for the misquote, the prop has not changed. symptoms started last season and i had it tuned over the winter hoping it may be prop damage. also besides showing 6-800 rpm loss the top end speed is also at least 5 knots lacking. as i stated, my current speed, per gps, is right where it always has been while turning 3200.

thanks for your thoughts!

[jleonard]

Have you checked the calibration on your tachometer? This is the number one issue from my experience that includes personal plus all the internet reading.
I would not be surprised if Bayside never thought to check this. My experience with them is much less than can be desired. I'll leave it at that.
Injectors are usually one of the very LAST things to check on a non performing diesel. Unless you have had water go thru your injection pump.
Injectors normally show signs when you have rough or hard starting or have lots of start up smoke.
Once you are up to power the injectors can just dump fuel, the engine will burn it.

[RobS]

But a misreading tach would not be consistent with his loss of top speed. Maybe a boost loss or an aftercooler issue? I agree injectors should be fine. Can try shooting each injector with an IR gun when running at whatever top rpm she will reach and look for any inconsistencies btwn the cylinders. Also try running off of a portable fuel container to rule out a fuel supply restriction.

[special k]

i was thinking some type of fuel restriction also. however acceleration is fine, up to the point of 3200.
i will however try to check my vents.

while i doubt i have a prop issue, if i were over propped would there not be other symptoms, or smoke?

i say this because last season i was soft aground near my dock during an extreme tide. but never a vibration after that. hale propeller tuned and balanced it for me and found no significant issues. if i am over cupped it would seem my soft grounding produced the same effect?? not likely in my mind

[RobS]

She requires quite a bit more fuel at WOT then she does at 3200rpm.. OK to check the vents but I would try the portable container. Verify no air restrictions into the engine room too.

That would be a considerable overpropping so symptons would be black smoke and high exhaust gas temperature. You were soft aground during an exterme tide? So I assume the boat was at rest not running when she went aground. She'd sit on the skeg, so certainly no worries there..

[special k]

thanks rob, i am confident it is not prop issue as nothing has really changed. got an e-mail into mack boring hoping for a response soon. not sure how to run the engine from a seperate fuel container, but it would help with the trouble shooting.

is that a simple task?

[RobS]

You can make connections at the top of the fuel strainer as well as other locations as it would be trial and error to eliminate different points in the fuel supply... Would be best to let your mechanic handle this as he probably already has a portable setup ready to go.

[special k]

for $120 per hour i'll handle a portable set up

[special k]

after sleepless nights pondering this issue i like the idea of running on a portable tank as a trouble shooting step. i will make this my next move. the boat runs well otherwise and fishing excursions and weekends are still happening, just at lower speeds.

any other suggestions or experiences welcome.....thanks

[special k]

after subscribing to boatdiesel.com i have discovered a wealth of information regarding low power in diesel engines. i believe my issue to be a fuel restriction and many possible reasons and solutions are detailed by the experts there. i will start with the simplest and work from there. article by tony athens regarding low power in marine diesels is very enlightening and easy to understand. well worth the price of membership, gives me ideas my paid professionals wouldn't speculate on.

will keep updated as i progress

[RobS]

Yes the BD site is a valuable tool, especially at $25. Be sure the throttle lever/linkage/cable etc. is not the culprit here. They can loosen and the throw be altered. Even though you get the rpm's no load, it's simple enough to disconnect and control it at the engine. With ear protection and a helper at the helm!

[special k]

rob, while looking through boatdiesel i noticed you post about a low power issue. what was your resolution?

still waiting to run mine on portable tank and get the fuel pressure checked.

[RobS]

rob, while looking through boatdiesel i noticed you post about a low power issue. what was your resolution?

still waiting to run mine on portable tank and get the fuel pressure checked.

Not low power, it was a discussion about fully loaded WOT.