Troubleshooting poor combustion

[F Angel]

I'm trying to troubleshoot poor combustion in a new-to-me Carver 450 Voyager with Volvo TAMD74P engines. I hadn't noticed any visible smoke in my first couple of outings but started getting heavy soot buildup on the stern after operating for a couple of hours. A couple of people commented that I must have "dirty" fuel. On my last outing I watched the stern closely and started noticing soot (heavier looking than smoke) swirling around the stern and under the dinghy. It appeared to come out of both exhausts, but a little heavier on the stbd side.
The fuel was loaded by the previous owner in approx Sept 2024 and tanks were about 7/8 full. I found a note from the previous owner stating that he experienced soot build up on the stern, heavier on the stbd side, when running about 1800 RPM (he wrote next to it "heavy load"). The engine hours on the note indicate it was written in early 2024. In Oct 2024 he had the props repitched from 28x31 to 28x29. This leads me to believe it isn't a fuel issue, but I have burned down the fuel to about 1/4 tank and tested for water at the bottom of the tank and found none. No issues with fuel filters. There is a slight residue on the tank sides as seen in the photo below but my feeling is that this isn't an issue.
While trying different speeds and observing the exhaust I was surprised that once I reached 2000 RPM the smoking appeared to stop. I couldn't say with certainty that this wasn't due to the air flow around the stern changing due to increased speed but I repeated this a couple of times and it truly looked like the smoking decreased or stopped. This leads me to thinking about the turbochargers. These turbos have wastegates. Is it possible that they are leaking by at lower loads and only when the engine is at higher power are they pumping sufficient air for combustion? Would both start leaking at the same time?
For info, injectors were rebuilt in Jun 2022 and valves adjusted then (about 300hrs ago). Just cleaned the K&N air filters. There are unfortunately no turbo boost gauges on this boat.
Bottom looked good at haul out in May. Max RPM reached at WOT was 2530 RPM

.

 

[Jeff F]

On planing boats like yours the engine is working at its absolute hardest when the boat is not quite on a full plane. That's the most plausible explanation for the soot at 1800 but not over 2000. You could well be over propped still as well. Doesn't sound like a fuel issue to me.

 

[F Angel]

Thanks Jeff. I should have noted that it was smoking throughout the power range up to 2000, although not noticeable at idle. That would lead me to believe that it isn't just overload causing the poor combustion. Although I'm surprised that after repitching 2 inches which I've read equates to about 300 RPM that it is still struggling to get to 2600RPM.

 

[O C Diver]

Is the boat bottom clean?

Do your engines have air filters? Often sooting can be an indication of not enough air flow relative to fuel burn. The filters that are cloth material, may not look dirty, but may be restricting flow. If they have these cloth type filters, they are cleanable with a special cleaner and then a water rinse following by several days of drying. Finally, they are lightly oiled before reinstalling.

It may look like this:

Ted

 

[Jeff F]

Although I'm surprised that after repitching 2 inches which I've read equates to about 300 RPM that it is still struggling to get to 2600RPM.

Based on conversations here over the years it wouldn't be a surprise if the repitching took it from grossly over propped to merely less over propped. If you can't get to full rated RPMs at WOT that adds support to the idea that you're still over propped.

Gross weight of the boat and bottom and prop condition also play a role. Make sure they're good first before repitching.

 

[rslifkin]

Based on conversations here over the years it wouldn't be a surprise if the repitching took it from grossly over propped to merely less over propped. If you can't get to full rated RPMs at WOT that adds support to the idea that you're still over propped.

Gross weight of the boat and bottom and prop condition also play a role. Make sure they're good first before repitching.

Could be overpropped, or it could be that the engines aren't making full power for some reason.

 

[KnotYet]

Is the boat bottom clean?

Do your engines have air filters? Often sooting can be an indication of not enough air flow relative to fuel burn. The filters that are cloth material, may not look dirty, but may be restricting flow. If they have these cloth type filters, they are cleanable with a special cleaner and then a water rinse following by several days of drying. Finally, they are lightly oiled before reinstalling.

It may look like this:

View attachment 166742

Ted

A really simple way to find out if the filters affect sooting would be to run without them and
check the transom.

To the OP, turbo boost gauges are fairly easy to install in the intake path. Knowing the pressure
is a good indication of a turbo's health. The same is true of pyrometers for the exhausts.

 

[Jeff F]

Could be overpropped, or it could be that the engines aren't making full power for some reason.

Yeah, but smoking at semi-planing speeds and not at planing speeds suggests otherwise IMO.

Not disagreeing, but I'd choose propping as the most likely cause.

 

[F Angel]

Is the boat bottom clean?

Do your engines have air filters? Often sooting can be an indication of not enough air flow relative to fuel burn. The filters that are cloth material, may not look dirty, but may be restricting flow. If they have these cloth type filters, they are cleanable with a special cleaner and then a water rinse following by several days of drying. Finally, they are lightly oiled before reinstalling.

It may look like this:

View attachment 166742

Ted

Yes, these are the filters it has. I found an unopened K&N filter cleaning kit on board and cleaned and oiled them but did not try running with them removed yet. I did run with the engineroom hatch open as I also had the thought that perhaps there was a restriction, but that was before it appeared to smoke less at the higher RPMs.

 

[F Angel]

A really simple way to find out if the filters affect sooting would be to run without them and
check the transom.

To the OP, turbo boost gauges are fairly easy to install in the intake path. Knowing the pressure
is a good indication of a turbo's health. The same is true of pyrometers for the exhausts.

I just came across the Yacht Devices site which has confirmed their J1708 Engine Gateway YDES-04 (Yacht Devices J1708 Engine Gateway for Volvo Penta EDC and J1587 engines) will connect to this engine. I should be able to pull out exhaust temps and turbo info as that must be data used by the electronic control. Looking forward to getting that installed as right now it's hard to troubleshoot with so little engine info.

​

 

[Gdavid]

Have the intercoolers been serviced according to schedule, if they are dirty, either on the air side or the sea water side, they won't cool the intake air adequately to provide the density of oxygen to provide the correct air fuel mixture, and you will get soot.

 

[F Angel]

Yes, these are the filters it has. I found an unopened K&N filter cleaning kit on board and cleaned and oiled them but did not try running with them removed yet. I did run with the engineroom hatch open as I also had the thought that perhaps there was a restriction, but that was before it appeared to smoke less at the higher RPMs.

Oh and yes bottom was clean 8 weeks ago. Could have a bit of growth now but i wouldn't think it would be heavy. I will be hauling out in a couple of weeks for a thruster repair/replacement so I will check and clean it at that time.

 

[F Angel]

Based on conversations here over the years it wouldn't be a surprise if the repitching took it from grossly over propped to merely less over propped. If you can't get to full rated RPMs at WOT that adds support to the idea that you're still over propped.

Gross weight of the boat and bottom and prop condition also play a role. Make sure they're good first before repitching.

I took off enough throw pillows that I probably picked up 50 RPM just with that!

 

[Kapn]

Bottom cleaning 8 weeks ago. Depending on where the boat is, water flow, growth rates, paint condition, etc. this could be a big contributor.
After haul out, with props fully clean and the barnacle husks sanded off, go for a full throttle run and check rpm. It should reach rated and hopefully exceed it. If not, then start checking aftercooler for cleanliness, boost pressure, injector condition, etc.

 

[KnotYet]

I just came across the Yacht Devices site which has confirmed their J1708 Engine Gateway YDES-04 (Yacht Devices J1708 Engine Gateway for Volvo Penta EDC and J1587 engines) will connect to this engine. I should be able to pull out exhaust temps and turbo info as that must be data used by the electronic control. Looking forward to getting that installed as right now it's hard to troubleshoot with so little engine info.

​

Good idea. Hopefully, your engine control modules will have stored any past fault codes, too.

 

[lwarden]

Does the engine turn the specified WOT revs?

 

[F Angel]

During the survey we were just barely able to reach 2600 RPM. That was with no dinghy. When I was out on this latest run I reached 2525 RPM.
I was able to track down the prop repitching to The Prop Shop in Seattle. I have to give them a shout out for being very helpful in researching this as the prop work was tied to the diver who was hired to bring them in and not the previous owner or boat. They believe that two inches they repitched is the limit to what they can do.

 

[Delta Riverat]

You are not that far off according to this. 2600 seems to be the top end.

 

[KnotYet]

You are not that far off according to this. 2600 seems to be the top end.

That 75 RPM is only 3% of 2600 RPM. If the tachs are within 3% you are doing just fine!

 

[rslifkin]

That 75 RPM is only 3% of 2600 RPM. If the tachs are within 3% you are doing just fine!

Agreed, I always say that accuracy of the tachs should be confirmed before chasing a low WOT RPM problem.

 

[lwarden]

Sounds like they got the props right on. This is where the boost pressure and EGT is going to come in handy. If there are sensors for both that can be read by the Yacht Devices translator then that sounds like a good path. Otherwise, adding an external gauge is pretty simple. Look up the Turbocator gauge from SBMAR. I have a similar one from Westach. Turbo-Boost/EGT NEW design | Westach

Just a guess that you will find low boost pressure. Perhaps a leaky connection from the turbo to intake?

 

[O C Diver]

Did you talk to the previous owner about what speed he ran the boat?

Have you loaded the boat (full fuel, water, and and everything you would take for extended cruising?

It seems to me the PO was trying to maximize economy at slower speeds by over pitching the propellers. If you're planning to run the boat under more power, you may have to switch propellers and reduce the pitch even more.

A note of caution:
Some boats won't get up on plane fully loaded from the factory. My boat from low liquids to full gained over 9,000 pounds on a 36,000 pound displacement boat. Add to that, the fuel tanks were too far aft to aid the boat getting over the bow wave. In essence, the boat could plane with 1/3 fuel tanks, but not full. Pretty disappointing!

Ted

 

[F Angel]

Agreed, I always say that accuracy of the tachs should be confirmed before chasing a low WOT RPM problem.

Fully agree. I have a hand held tach that I tried to use to confirm the gauges but unfortunately some rust/paint spots on the shaft where I had stuck the reflective tape must have been interfering with the scope as I couldn't get consistent readings. Wire brushed and painted that area so hopefully I can get a reading with confidence next time out.

 

[F Angel]

Did you talk to the previous owner about what speed he ran the boat?

Have you loaded the boat (full fuel, water, and and everything you would take for extended cruising?

It seems to me the PO was trying to maximize economy at slower speeds by over pitching the propellers. If you're planning to run the boat under more power, you may have to switch propellers and reduce the pitch even more.

A note of caution:
Some boats won't get up on plane fully loaded from the factory. My boat from low liquids to full gained over 9,000 pounds on a 36,000 pound displacement boat. Add to that, the fuel tanks were too far aft to aid the boat getting over the bow wave. In essence, the boat could plane with 1/3 fuel tanks, but not full. Pretty disappointing!

Ted

I haven't been able to get hold of the previous owner just yet, but trying. The specified weight of the boat from the factory with full tanks is 39,600 lbs. At haul out with 3/4 fuel tanks and empty black water and 1/4 full water tanks she weighed in at 36,000 lbs per the travel lift scale. No idea how accurate their scale is but that seems light.
Ultimately the question here is why is she smoking so much now. I didn't notice this buildup while running during the survey. The only difference I can point out is that we didn't have the dinghy on the stern during the survey.

 

[F Angel]

Sounds like they got the props right on. This is where the boost pressure and EGT is going to come in handy. If there are sensors for both that can be read by the Yacht Devices translator then that sounds like a good path. Otherwise, adding an external gauge is pretty simple. Look up the Turbocator gauge from SBMAR. I have a similar one from Westach. Turbo-Boost/EGT NEW design | Westach

Just a guess that you will find low boost pressure. Perhaps a leaky connection from the turbo to intake?

Thanks for the link. Yacht Devices confirmed this morning that their translator can read this engine so I'm ordering two today. Trying to troubleshoot without any engine info is frustrating.
I'm still wondering about the wastegates leaking by as that would explain insufficient air at low RPMs (as indicated by smoke/soot) and sufficient air at the top range, where the wastegate would normally open anyway (as indicated by the apparent lack of smoke/soot).

 

[F Angel]

Bottom cleaning 8 weeks ago. Depending on where the boat is, water flow, growth rates, paint condition, etc. this could be a big contributor.
After haul out, with props fully clean and the barnacle husks sanded off, go for a full throttle run and check rpm. It should reach rated and hopefully exceed it. If not, then start checking aftercooler for cleanliness, boost pressure, injector condition, etc.

Thanks Kapn

 

[rslifkin]

Thanks for the link. Yacht Devices confirmed this morning that their translator can read this engine so I'm ordering two today. Trying to troubleshoot without any engine info is frustrating.
I'm still wondering about the wastegates leaking by as that would explain insufficient air at low RPMs (as indicated by smoke/soot) and sufficient air at the top range, where the wastegate would normally open anyway (as indicated by the apparent lack of smoke/soot).

If the previous owner rarely or never ran the engines hard, it's possible. I've seen carboned up waste gates stick closed. Sticking open is less common, but certainly possible.

 

[O C Diver]

The only difference I can point out is that we didn't have the dinghy on the stern during the survey.

How much does the dinghy weigh?

There can be a significant change in bow angle with a significant weight on the swim platform.

Simple test, take the dinghy off the platform and see if your trim improves.

Also, on my boat, the fuel tanks are about 12' long. At half full, the fuel in the tanks shifts to the back, exacerbating the trim angle.

What does the boat's trim and wake look like? The bigger the wake and the deeper the stern sits, the less efficient the boat is (harder the engine works). In a perfect world, when the boat gets on plane, the bow angle should drop substantially (maybe half of what it took to get on plane).

Ted

 

[rslifkin]

How much does the dinghy weigh?

There can be a significant change in bow angle with a significant weight on the swim platform.

Simple test, take the dinghy off the platform and see if your trim improves.

Also, on my boat, the fuel tanks are about 12' long. At half full, the fuel in the tanks shifts to the back, exacerbating the trim angle.

What does the boat's trim and wake look like? The bigger the wake and the deeper the stern sits, the less efficient the boat is (harder the engine works). In a perfect world, when the boat gets on plane, the bow angle should drop substantially (maybe half of what it took to get on plane).

Ted

All very good points.

Although on my boat with generously sized trim tabs, I've found that added weight aft has a pretty small impact on planing performance. The boat takes a hair longer to climb onto plane and runs with more tab down, but doesn't run much slower. Even a difference of 1500 lbs in the aft mounted fuel tanks is small. However, it's sensitive to weight forward. A few hundred pounds forward will slow the boat by a few tenths of a knot, as there's no way to add lift forward, so you end up with less tab deployed and less total lift to get the fastest running angle. And that means the boat is not planing as high in the water at a given speed, so there's more drag. Just 1 person walking from the stern to the bow will lose 0.1 - 0.2 kts and no trim adjustment will get it back.

 

[lwarden]

Thanks for the link. Yacht Devices confirmed this morning that their translator can read this engine so I'm ordering two today. Trying to troubleshoot without any engine info is frustrating.
I'm still wondering about the wastegates leaking by as that would explain insufficient air at low RPMs (as indicated by smoke/soot) and sufficient air at the top range, where the wastegate would normally open anyway (as indicated by the apparent lack of smoke/soot).

Turbo, wastegate and all plumbing are good suspects. I like the way you are thinking.