Troubleshooting poor combustion

[Lepke]

Injector tips can have buildups that disrupt some or all of the spray pattern. It causes bigger droplets in the disrupted area. Larger droplets don't fully combust and exit as soot or raw fuel. Injector tips can be cleaned manually or with additives in the fuel. They cause the combustion to raise temps that burn off the buildups. One way is to fill your secondary filter with Seafoam and run the engine hard. It takes a couple hours as the Seafoam is gradually diluted with fuel.
In the old days we would run a tank of #1 diesel a couple times a year.

 

[bykpjfk]

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
View attachment 166722.

A cheap thing to try is adding the appropriate amount of a product called 'Diesel Klean'. Available at walmart. Increases cetane rating of diesel and has some cleaning properties.

 

[RickyD]

Just to add to the discusson my port Cat 3208TA engine started smoking at higher rpms and it was the turbo. There was some rust and carbon build up that stopped the turbo from spinning properly. I little dremel work and she spins at idle now. No more smoke.

 

[F Angel]

A cheap thing to try is adding the appropriate amount of a product called 'Diesel Klean'. Available at walmart. Increases cetane rating of diesel and has some cleaning properties.

That was my thinking. I ended up dosing with both Biobor MD and Biobor JF.

 

[F Angel]

Just to add to the discusson my port Cat 3208TA engine started smoking at higher rpms and it was the turbo. There was some rust and carbon build up that stopped the turbo from spinning properly. I little dremel work and she spins at idle now. No more smoke.

I used a borescope to get a look at the exhaust side and it looked like the soot buildup was minor and even, and a look at the blower wheel gave me the same impression. Spun easily by hand. Interesting you were able to get her cleaned up with a dremel. I've always been so concerned about creating an imbalance that I don't try to clean anything in place, but if you can remove it and do a full cleaning that would be great.
I received my YDES-04 gateway but have had an issue getting the proper files loaded into them to read port and stbd engines correctly. Support from yachtdevices has been good, but dealing with some of this computer code isn't my strength. I am able to now see on one engine Boost and Fuel Flow along with temps, RPM etc. As soon as I can get this working on the other engine I'll take her out and run through the RPM range and observe exhaust and record data. Burn down the last of the old fuel and then load up with fresh fuel also.

 

[Jeff F]

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.

Let's remember here that the OP has a planing boat, and as I understand things there is no smoke at planing speed.

My understanding from reading some of your comments here (and I'm pretty sure it's one of Tony Athens key points) is that operating at semi-planing speeds is a danger zone.

It may seem flip, but maybe a bit of smoke getting up on plane is completely acceptable on this type of boat. Just don't cruise at that speed.

ETA: everyone I've met with similar boats tell me they run at < 10 knots or > 20. Maybe others can chime in.

 

[Jeff F]

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.

What speeds were you running?

 

[rslifkin]

Let's remember here that the OP has a planing boat, and as I understand things there is no smoke at planing speed.

My understanding from reading some of your comments here (and I'm pretty sure it's one of Tony Athens key points) is that operating at semi-planing speeds is a danger zone.

It may seem flip, but maybe a bit of smoke getting up on plane is completely acceptable on this type of boat. Just don't cruise at that speed.

ETA: everyone I've met with similar boats tell me they run at < 10 knots or > 20. Maybe others can chime in.

Agreed, there's rarely a reason to run at semi planing speeds. Nasty following seas is about the only one I can think of. For us, if we want to go faster than 7 kts then it's time to get the boat on plane, which means 14-15 kts minimum, up to about 18 at max continuous. The 7-14 kt range means running bow high, plowing a huge wake, high engine load and high fuel consumption (per mile it's probably as bad or worse than being on plane).

Just how bad that hump range is will depend on the boat, but it's never really a good place to run with a planing hull.

With diesels I'd expect a quick throttle up to get on plane may produce a bit of smoke for a few seconds. But even in the plowing range I wouldn't expect any significant steady state smoke, at least not with electronically controlled diesels where fueling is limited based on boost.

 

[Jeff F]

With diesels I'd expect a quick throttle up to get on plane may produce a bit of smoke for a few seconds. But even in the plowing range I wouldn't expect any significant steady state smoke, at least not with electronically controlled diesels where fueling is limited based on boost.

Not heavy smoke, but more than normal when the engines are working at > 90% capacity, which on this boat may be in the 1500-1800 rpm range.

 

[F Angel]

Injector tips can have buildups that disrupt some or all of the spray pattern. It causes bigger droplets in the disrupted area. Larger droplets don't fully combust and exit as soot or raw fuel. Injector tips can be cleaned manually or with additives in the fuel. They cause the combustion to raise temps that burn off the buildups. One way is to fill your secondary filter with Seafoam and run the engine hard. It takes a couple hours as the Seafoam is gradually diluted with fuel.
In the old days we would run a tank of #1 diesel a couple times a year.

Interesting suggestion about filling the secondary filter with Seafoam. I had pushed injectors down the list as they had been pulled two years ago for "overhaul". I don't know if they replaced tips at the time or just pop tested them and put them back in.

 

[F Angel]

Agreed, there's rarely a reason to run at semi planing speeds. Nasty following seas is about the only one I can think of. For us, if we want to go faster than 7 kts then it's time to get the boat on plane, which means 14-15 kts minimum, up to about 18 at max continuous. The 7-14 kt range means running bow high, plowing a huge wake, high engine load and high fuel consumption (per mile it's probably as bad or worse than being on plane).

Just how bad that hump range is will depend on the boat, but it's never really a good place to run with a planing hull.

With diesels I'd expect a quick throttle up to get on plane may produce a bit of smoke for a few seconds. But even in the plowing range I wouldn't expect any significant steady state smoke, at least not with electronically controlled diesels where fueling is limited based on boost.

I know this sounds stupid but I haven't been able to clearly tell when I've passed the transition point and am up on plane. I know I'm on plane at 2000 and I'm not at 1300, but I just don't notice the change enough to where I can say, yeah I'm now just up on plane and this is a good place to run. I need to get her out and work back and forth through the range to get a better feel. Now that I have fuel flow displayed that should help me as well.

 

[Jeff F]

I know this sounds stupid but I haven't been able to clearly tell when I've passed the transition point and am up on plane. I know I'm on plane at 2000 and I'm not at 1300, but I just don't notice the change enough to where I can say, yeah I'm now just up on plane and this is a good place to run. I need to get her out and work back and forth through the range to get a better feel. Now that I have fuel flow displayed that should help me as well.

I'd say that you shouldn't linger between 1300 and 2000 as a general rule. Effectively you have a two-speed boat.

 

[Jeff F]

Maybe @ranger58sb can comment, as he has a somewhat similar boat.

 

[SteveK]

@F Angel
Do you use the exhaust/engine sound? I listen to the tone to balance, ignoring 2nd gauge after setting one to say 2000 I sync by sound. The same can be for on plane or not as the sound changes as the boat gets on step.

 

[rslifkin]

I know this sounds stupid but I haven't been able to clearly tell when I've passed the transition point and am up on plane. I know I'm on plane at 2000 and I'm not at 1300, but I just don't notice the change enough to where I can say, yeah I'm now just up on plane and this is a good place to run. I need to get her out and work back and forth through the range to get a better feel. Now that I have fuel flow displayed that should help me as well.

On some boats the bow will drop noticably once the boat climbs fully onto plane. The better indicator however is your wake. When the boat makes it fully onto plane you'll see the flow separate from the transom and break off cleanly. At plowing speeds you're still dragging water along behind you as a frothy, turbulent mess, much like a planing hull does below hull speed, just much more of it (and with a bigger wake). When the boat gets on plane you won't see that anymore, you'll see water streaming cleanly off the transom and making a wake a bit further behind you.

 

[ranger58sb]

Maybe @ranger58sb can comment, as he has a somewhat similar boat.

I'm afraid I don't have much to offer that hasn't already been mentioned.

One, though, is about achieving rated WOT. If the engine is rated for 2600, the usual recommendation is to get it to 2650 with full fuel and water load, and ideally with ~4-ish pax. (For our 2300 engines, the maker's recommendation is 2300 @90% load). That means 2525 would still be struggling... so continuing to chase "rated WOT plus 50" (-ish) would likely be good. If the props are pitched as much as possible, maybe adding or subtracting some cup might have further impact.

Injectors, turbos, wastegates, aftercoolers (air side), raw water plumbing, etc. all still seem to be potentially related.... and it sounds like OP is pursing all those appropriately.

The 'on plane or not?" part -- and maybe how fast OP is getting there -- could be a thing. Gradually cranking the engines up could be prolonging the "not on plane" period, whereas putting the pedal to the metal to get up to 2000 (-ish) more quickly might be a useful diagnostic exercise. Might also be useful to poll other 450 Carver owners about planing speeds (RPM), see how they compare with OPs situation. (I'd have guessed anywhere from ~1700 and up would be on plane, sometimes maybe best achieved at that lower end by running up to higher (~2000?) and then bringing the boat back down. (Does smoke linger?) All that about engine sync (by sound) and wake.)

If it turns out the smoke is only during that heavy acceleration phase, and the engines can eventually achieve "rated WOT plus ~50" could be there's no problem to solve... or could maybe need a Volvo-whisperer for additional improvement.

??

-Chris

 

[mvweebles]

I know this sounds stupid but I haven't been able to clearly tell when I've passed the transition point and am up on plane.

Don't feel stupid. Unless it's a really fast boat (25+ kts), I have a hard time telling the difference between a fast snowplow and true plane. Looking at the wake is pretty informative.

Peter

 

[rslifkin]

Don't feel stupid. Unless it's a really fast boat (25+ it's), I have a hard time telling the difference between a fast snowplow and true plane. Looking at the wake is pretty informative.

Peter

Exactly. Slower planing hulls tend to be propped for a bit better low speed thrust and also have a lower minimum planing speed. So they tend not to get on plane as dramatically as a fast boat.

 

[Jeff F]

Exactly. Slower planing hulls tend to be propped for a bit better low speed thrust and also have a lower minimum planing speed. So they tend not to get on plane as dramatically as a fast boat.

I'd categorize this boat as a faster planing hull. Top speed on a review I read was close to 30 knots. I've watched the bigger sister 540 plane off, and it's fairly dramatic.

This is based only on casual observation and chatting with owners.

 

[F Angel]

Finally got the boat out a couple of times this week to take readings at various speeds and monitor the smoke and recorded some very interesting data.
I have the Yacht Devices YDES-4 gateway now installed which pulls data from the EDC (Electronic Diesel Control) so I could now monitor turbo boost and fuel flow.
Made several runs starting at 1000 RPM and working in 100 RPM increments up to WOT which on all runs turned out to be 2500 RPM.
I made runs in opposite directions (mostly because of running out of room) and ran at each step for about a minute. I won't post all the data but here is what I found out.

1. Both engines ran clear to a very light brown haze between 1000 and 1300RPM (7.3-8.6kts).
2. The stbd engine started smoking black at 1400 RPM, the port engine started smoking black at 1500 but lighter than the port. At 1800 RPM both engines had heavy black smoke which was swirling up on the transom.
3. At 1900 RPM the black smoke was still present but lighter, and less on port than stbd.
4. At 2000 RPM the smoke was mostly clear and at 2100 and above there was just the light brown haze in the wake.
5. At 1300 RPM, with an avg speed of 8.5kts, fuel flow on both engine was even at about 4.4 gal/hr, and boost was also even at 16.5PSI
6. Above this speed the fuel flow on the stbd engine started to diverge higher and the turbo boost diverged lower on the stbd than the port.
7. At 1900 RPM, with an avg speed of 12.0 kts, fuel flow on port was 12.2gal/hr vs 13.3 on stbd; port boost was 28.0 PSI vs 25.7PSI on stbd.
8. At 2200 RPM, with an avg speed of 15.8kts, fuel flow on port was 17.6gal/hr vs 18.6 on stbd, port boost was 36.1 PSI vs 32.5PSI on stbd.
9. At 2500 RPM, with an avg speed 20.3kts, fuel flow was even again at 26.6 gal/hr, and boost was even at 41.5 PSI

No rudder movements were made during the run and no trim tab adjustments. Some current and wind present but typical conditions.
The boat appears to get up on plane around 16-1700 RPM

The performance of the Stbd engine correlates with the heavier smoke on that engine. Up until 2500 RPM the readings indicate an issue with the stbd engine - fouled turbos or charge air cooler perhaps? I don't understand yet how the boost on the stbd engine catches up to the port at 2500 and the fuel consumption equalizes. Need to think on that one for a bit.

Also, I finally went below and checked the Racor gauges while at 2000 RPM. The port differential was 6"Hg and the stbd was 13"Hg! I should have caught that earlier. I don't know what the maximum vacuum lift is for the TAMD 74 engines but 13"HG is in the red area of the gauge and probably a major factor in the boat's inability to reach 2600 RPM.
So next step is to change filters and then run the sea trial again.

 

[ranger58sb]

Also, I finally went below and checked the Racor gauges while at 2000 RPM. The port differential was 6"Hg and the stbd was 13"Hg! I should have caught that earlier. I don't know what the maximum vacuum lift is for the TAMD 74 engines but 13"HG is in the red area of the gauge and probably a major factor in the boat's inability to reach 2600 RPM.
So next step is to change filters and then run the sea trial again.

Maybe. Good to fix that and recheck.

But if that turns out to be not a factor... it still remains that you can only reach 2500 and should be able to hit ~2650.

Assuming clean bottom, props can still be one cause. Don't know enough to know others...

-Chris