Yanmar Down on Revs

[Dockhead]

My 4JH3HTE normally revs happily up to its 3800 rpm redline. Today, after a long lazy motor at 1500 - 1700 rpm (not in a hurry, enjoying the spectacular dead calm day, letting the tide do the work) from Yarmouth up to Cowes after the Old Gaffer Festival, and after nearly an hour idling while hovering around the Cowes fuel barge waiting for a giant mobo to suck however many thousands of liters go into its tanks, I decided to blow out the cobwebs, as I usually do, with a few minutes at full throttle.

Imagine my disappointment when I couldn't make more than 3300 rpm. After application of full throttle, revs would go up to 3500 or so, then quickly drop down to 3300 or even 3200. No black smoke, engine perfectly smooth, just no revs

I had a similar incident a couple of years ago when got caught in a violent gale crossing the Channel at night. That case was much worse, however - revs down to 2300 or so IIRC. It turned out then that oil got splashed into the intake from the violent motion of the boat (and possible overfilling of the engine), and gummed up the turbo. Problem quickly disappeared and I had several hundred hours of trouble free motoring afterwards.

Guys, what do you think?

[tropicalescape]

Fuel pump?bad filter?jets clogged?..Good luck..DVC

[Florida Mike]

Foulwd prop,exaust cloged. Jst my 2 cents, Mike.

[Dockhead]

Revs easily to 4000 out of gear. WTF?

[donradcliffe]

All that time running below the boost level made your turbo unhappy.

[perchance]

Is your turbo coked up?

[Dockhead]

Originally Posted by perchance

Is your turbo coked up?

I don't know -- how do you tell? Just yesterday it ran fine.

[perchance]

Originally Posted by Dockhead

I don't know -- how do you tell? Just yesterday it ran fine.

Some dis assembly required. I don't know the specifics of your engine but you need access to the exhaust inlet to the turbo or outlet if that is easier, to check for carbon build up. Do you put a lot of hours on the engine at low rpm?

[Ex-Calif]

No smoke to me means no excessive load. Low rpm could mean incomplete insufficient fuel/air charge.

I'm in the turbo camp at this point.

[capngeo]

This might sound like lunacy, but spray some water into the intake while running at WOT... A trigger bottle is all you need.... The steam will help decarbon the turbo... If that doesn't fix it, look elsewhere

[Dockhead]

Originally Posted by perchance

Some dis assembly required. I don't know the specifics of your engine but you need access to the exhaust inlet to the turbo or outlet if that is easier, to check for carbon build up. Do you put a lot of hours on the engine at low rpm?

It's not all that hard to get to. Half an hour of work, I think. I'll have a look today. I think Yanmar prescribe washing the turbo from time to time, don't they? Maybe that's what's needed.

[Dockhead]

Originally Posted by Ex-Calif

No smoke to me means no excessive load. Low rpm could mean incomplete insufficient fuel/air charge.

I'm in the turbo camp at this point.

Sounds logical given (a) no smoke; and (b) revs smoothly to redline without a load.

The turbo was overhauled about 500 hours ago - I think it should be basically sound. Maybe really it got carboned up with all that slow running.

I do not ordinary motor at 1500 rpm, nor do I usually idle for an hour at a time. So maybe that is what caused it.

[mrm]

I remember we had a similar thread here recently: http://www.cruisersforum.com/forums/...ear-78978.html

I would suggest rigging a temporary gravity fed fuel supply bypassing all filters, and see what happens before digging into the turbo.

To me 'revs easily without load' together with 'no smoke' looks like a fuel deficiency issue. When there is too little oxygen (as when turbo/air system is at fault) I would expect to see some black smoke.

[tropicalescape]

What was the Problem ?..DVC

[Dockhead]

Still don't know. I tried running it today under more load and periodically flooring it, with no improvement. Tomorrow I'll check for fuel restrictions and maybe wash the turbo.