Volvo Penta KAD 300 weird fueling issue

[briggs]

Hi,
I have had a weird issue pop up with my KAD 300A, hope someone can shine a light on it.
A little background the engine. Very well maintained 3300 hrs on the clock. Never had any major issues. New injectors at 3000 Hrs, Valve lash checks every 300 hrs, No turbo or supercharger issues. Oil and Filter changes every 100 hrs, No over heating issues runs 185 deg at cruise of 3000-3100RPM. Never have had any trouble making WOT. Engine is ran 300-400 hrs a year.
So the other day running in from an offshore island 40 mi run, I noticed the engine was surging or hunting -RPM fluctuating between 2950 and 3100.
Then tried to see if I could make wide open throttle. When throttle was pushed all the way forward it took a bit for engine to build any fuel pressure to reach Wot. When throttle was pulled back it took a bit for RPM to come back down to 3000 and surging/ hunting continued. No stalling or throttle issue below 2800 rpm.
First thought was dirty fuel filters so I replaced both the spin on filter on the engine and the Racor, I don't run marine diesel and have had no fuel moisture issues, this offered no change in problem. Boost seems ok because it is not falling into supercharger range to build boost back up. I checked for moisture at T on the bottom EDC it is dry as a bone. No Codes have shown up on EDC display either.
I have read some of Volvopauls threads. So I have a new stop solenoid spring on order.
I Have identified the location of a boost sensor on the manifold as well as in the EDC unit, should those be replaced as well?
Any insight or help is always appreciated
Thanks

 

[kashurst]

although your revs only go down to 2950, it does sound like a boost pressure issue. The ecu will only provide enough fuel for the available pressure, not the other way around.
Have you calibrated your rev counter recently? Can you get a volvo tech onboard with a vodia box to check what the turbo is doing? You could take the exhaust elbow off and have a look inside the turbo. The vanes on the exhaust impeller run very very close to the housing, if there is even a small gap they don't work very well. If they are the originals after 3000 hours and nearly 20 years that is incredible.

 

[Portofino]

Agree ^^ classic turbos on its way out .The intermittent hunting under 3000 rpm is the tell tale sign .
Its insidious.
Bearings as have a life in a tough environment, linked to oil quality and as said above the vane tips wear effectively burn there tips + some casing corrosion = the fit degrades .

Although it sounds you have done very well with it with regular use .Poor quality oil speeds up the turbo bearing wear and overloading the engines accelerates the vane tip shrinkage .This from fouling and or excess weight creeping up on the boat .

I got to 1000 hrs on a sports cruiser and the turbo thing was diagnosed by techies , I sold it on .
Started with a stutter once every once in while over a 3 hr cruise , then every hr , the down hunting around 3000 rpm periods got longer and longer .
Apparently a visual look is pretty meaningless as you can’t see the bearings or determine axial play tolerances with your fingers .
If the vane gap is massive it will be way past the hunting @ 3000 rpm stage by now .

Another disturbing sign is orange spots on the outside of the exhaust elbow , not related here to your issue ( I think ?* ) thats made of a metal thats rots from the inside out and the water outlets corrode closed .Very poor execution of that part design and build wise .
Its connected by a rubber ring thing to the exhaust horn on a outdrive boat ( yours is not a outdrive thank your lucky stars ) .
This rim or edge where the rubber ring fits rots , crumbles away making refitting a challenge.

You can now get after market stainless steel exhaust elbows and other bits for those interested .


* If the spray ducts have closed up from corrosion then the exhaust gases temps could back up into the exhaust side of the turbo = additional heat = additional wear factor = shortened life .Crucially below par turbo performance starting to creep in .The boost pressure drops as it can’t fully spin up because the exhaust gases heating up .Only had to drop a few %.
But they are not closed up enough to see any change that you notice in the exhaust smoke colour …….Yet !
All insidious, starts un noticed and creep in becomes the norm .

To get to eye ball the turbo vanes and internal housing FWIW , you need to remove the elbow ( see the condition if the spay ducts ) ……two birds with one stone springs to mind .

 

[briggs]

Thank you all for your response.
portofino my engine is on a drive! I am aware of the turbo issues, and I suspected that my turbo would need replacement soon. I was not aware that the symptoms would look like they do.
I have changed riser over to a stainless unit and have been happy with it.
Rev counter is crossed referenced with MFD info, and appears to be accurate.
The turbo does have over 10 years of service!

 

[A_8]

3300h and an outdrive without major issues is truly impressive and somewhat inspiring, I think the designlife on the drive is 2000h and 4000h on the engine before major refurb.
Maybe the 3-400h per year helps or the duty cycle is light torque with enough high torque every now and then, anyways it's really good and you should get new turbos and probably a few other bits.

 

[briggs]

3300h and an outdrive without major issues is truly impressive and somewhat inspiring, I think the designlife on the drive is 2000h and 4000h on the engine before major refurb.
Maybe the 3-400h per year helps or the duty cycle is light torque with enough high torque every now and then, anyways it's really good and you should get new turbos and probably a few other bits.

Thanks,
I have kept the engine corrosion free with a bone dry bilge. It’s been on a trailer it’s entire life. So freshwater rinsed after every use. Cruise RPM not to exceed 3100 . Routine maint has included replacement of key parts. IE: coolers, pumps, belts etc…
The drive in the otherhand only have been getting 1200 hrs or so before rebuild or replace

 

[briggs]

3300h and an outdrive without major issues is truly impressive and somewhat inspiring, I think the designlife on the drive is 2000h and 4000h on the engine before major refurb.
Maybe the 3-400h per year helps or the duty cycle is light torque with enough high torque every now and then, anyways it's really good and you should get new turbos and probably a few other bits.

What else do you suggest?

 

[A_8]

If you have kept the engine bone dry and freshwater rinsed every time maybe not much. Normally and IIRC the circulation pump starts to leak, the seawater pump gets worn and loose pumping power and leaks, the oil cooler gets corroded, exhaust elbow corrodes/crack.

 

[briggs]

Those have all been addressed as they all have reared there ugly side!