Yanmar 2gm20f - Black Water at 2700+ RPM

[Jesgatt]

Originally Posted by Compass790

I think you are overpropped for a start. You should be propped to be able to get to max revs driving. 2700 is quite a bit short.
Compression sounds fine.
Shouldnt be timing issue since you changed nothing but you could check it.
Check the governor & fuel rack linkages for smooth operation.
Best not to run it at black smoke blowing levels as it's not good for anything, just throttle back a bit till it burns clean.

We are overpropped too (Worse than yours) & have to monitor exhaust smoke.
You havent fitted a bigger alternator or anything like that have you?

The issue is that when I bought the boat (2 years ago) I could reach 2700rpm easily without any issues (no black water and smoke). I then did a service and overfilled a bit the oil. When I was running, I heard like a backing from the exhaust and from that day the engine started to emit black water. Oil level never goes down, so it is not a ring issue. Someone suggested that I check the fuel tank for any residues - I will also do that next week, since tanks is full now.

Thanks

[Sailmonkey]

Originally Posted by Wotname

Err... No.

Jesgatt has a 2GM20 which is raw water cooled so no coolant pump.

I clearly see 2gm20F (F for fresh) in the Thread title.

I’ve seen the Pre combustion chambers crack causing poor fuel burn at higher deliver rates.

[Wotname]

Originally Posted by Sailmonkey

I clearly see 2gm20F (F for fresh) in the Thread title.

I’ve seen the Pre combustion chambers crack causing poor fuel burn at higher deliver rates.

While you do see that, you might not have been reading the fine print...

You might not have noticed that this thread was started in mid-February 2010 by cfoxcvg and was mainly completed by the end of February 2010 with a final post by cfoxcvg (post #24).

Fast forward 11+ years to yesterday and Jesgatt revives the thread with his own question in post #25. Jesgatt clearly states in his post he has 2GM20 raw water cooled engine.

Details are important when trying to help others with mechanical issues!

[Compass790]

Originally Posted by Jesgatt

The issue is that when I bought the boat (2 years ago) I could reach 2700rpm easily without any issues (no black water and smoke). I then did a service and overfilled a bit the oil. When I was running, I heard like a backing from the exhaust and from that day the engine started to emit black water. Oil level never goes down, so it is not a ring issue. Someone suggested that I check the fuel tank for any residues - I will also do that next week, since tanks is full now.

Thanks

Arrgh! Just lost my post as net dropped out.
Start agin, sigh.
Ok Jesgatt, understand now you are not worried about overpropping just concerned about black smoke change in behaviour, rightly so.
Black smoke as you described is caused by many things ( basically too much fuel in the combustion chamber for the amount of oxygen ) but as you have good compression and have had injectors etc checked the likely ones left are restricted air or exhaust.
Try taking air- cleaner off. I think original air cleaner are just mufflers really & dont restrict air flow if clogged in the foam but check that.
Check exhaust hoses, I know you have done the elbow.
Doubt very much if diesel tank residues are your problem, that would be fuel starvation, not excess.
Cant see how overfilling the oil would cause yr issue.

I've run outa ideas now, following with interest to see what the solution is.
good luck with diagnosis & cure

[skipperpete]

The high idle rpm should be more than 3400 but not knowing the accuracy of your tacho or whether the alternator has gone rogue stalls that line of investigation so I’ll try this.... I reckon one of your cylinders is having a bit of a bludge, but fuel related and possibly the injector pump. If one of the elements is scored, injected volume drops and the other cylinder cops the heavy lifting and you get black smoke. Also a faulty delivery valve can cause trouble in the form of injector dribble from injection echoes ( the valve is there to stop exactly this). If I was the guy you hired to fix this my next move would be to open an injector line to see if you have a weak cylinder..... but not at idle and not with a decomp lever. If the mooring lines are good, run the engine in gear at between 1,000 and maybe 1,500 if you feel comfortable with its behaviour and see how balanced the cylinders are. If you have a weak cylinder the smoke will increase when it drops out.
Watch the tacho and record rpm drop.... don’t do this diagnostic alone and only at lower rpm if you get a shake up. Be prepared for a little bit of fuel leakage , use rags to soak up the diesel and don’t put your fingers near the open union.
Other than that, I’d probably take off the exhaust manifold ...and the intake manifold to see if she’s really coked up in the ports.
Pete

[Wotname]

Originally Posted by skipperpete

The high idle rpm should be more than 3400 but not knowing the accuracy of your tacho or whether the alternator has gone rogue stalls that line of investigation so I’ll try this.... I reckon one of your cylinders is having a bit of a bludge, but fuel related and possibly the injector pump. If one of the elements is scored, injected volume drops and the other cylinder cops the heavy lifting and you get black smoke. Also a faulty delivery valve can cause trouble in the form of injector dribble from injection echoes ( the valve is there to stop exactly this). If I was the guy you hired to fix this my next move would be to open an injector line to see if you have a weak cylinder..... but not at idle and not with a decomp lever. If the mooring lines are good, run the engine in gear at between 1,000 and maybe 1,500 if you feel comfortable with its behaviour and see how balanced the cylinders are. If you have a weak cylinder the smoke will increase when it drops out.
Watch the tacho and record rpm drop.... don’t do this diagnostic alone and only at lower rpm if you get a shake up. Be prepared for a little bit of fuel leakage , use rags to soak up the diesel and don’t put your fingers near the open union.
Other than that, I’d probably take off the exhaust manifold ...and the intake manifold to see if she’s really coked up in the ports.
Pete

Excellent advice IMO and allow me to correct a very small inaccuracy; the alternator will have zero effect on the tacho reading as the 2GM20f uses a tacho sensor on the flywheel.

If you wish to verify the tacho, use a free strobe tacho app for your smartphone. Google will lead you towards a good one.

As mentioned upthread but work repeating, check your entire exhaust hose - the internal layers may have delaminated and be causing a partial blockage.

[Compass790]

Max neutral rpm shud be 3825.
Thanks for tip about smartfone app Wottie, will have to check it out.

+2 for skipperpetes diagnostic approach

[skipperpete]

Oops, the bit about the alternator was not related to the tacho accuracy but to the fact that it’s the only parasitic load that can easily be removed from the equation. I’ve seen the alternator on a 3GM 30F hold the rpm to below 1,000 at full throttle because of an incorrectly adjusted smart regulator..... it laid a thick layer of soot on the water around the exhaust outlet at the stern.

[Wotname]

Originally Posted by skipperpete

Oops, the bit about the alternator was not related to the tacho accuracy but to the fact that it’s the only parasitic load that can easily be removed from the equation. I’ve seen the alternator on a 3GM 30F hold the rpm to below 1,000 at full throttle because of an incorrectly adjusted smart regulator..... it laid a thick layer of soot on the water around the exhaust outlet at the stern.

Oh, I see what you were getting at with the alternator - good point

[Jesgatt]

Originally Posted by Compass790

Arrgh! Just lost my post as net dropped out.
Start agin, sigh.
Ok Jesgatt, understand now you are not worried about overpropping just concerned about black smoke change in behaviour, rightly so.
Black smoke as you described is caused by many things ( basically too much fuel in the combustion chamber for the amount of oxygen ) but as you have good compression and have had injectors etc checked the likely ones left are restricted air or exhaust.
Try taking air- cleaner off. I think original air cleaner are just mufflers really & dont restrict air flow if clogged in the foam but check that.
Check exhaust hoses, I know you have done the elbow.
Doubt very much if diesel tank residues are your problem, that would be fuel starvation, not excess.
Cant see how overfilling the oil would cause yr issue.

I've run outa ideas now, following with interest to see what the solution is.
good luck with diagnosis & cure

Hi,
Apart from checking myself, I also brought a Yanmar Mechanic. He checked the pre-combustion chambers for any cracks and he said that they are ok. To be on the safe side, I also replaced the exhaust pipe and checked both the waterlock and muffler for any blockages, but everything seemed fine. After changing the exhaust pipe, the problem still remained there. I also checked the air cleaner and it is clean.
I have also run out of any ideas (apart from having an issue with the diesel pump). At this time any suggestions will be considered.

Note: I tested the engine off load and this time I was not afraid to push the throttle down to a max - I got the engine to rev to 3800+. I tested the engine both on mooring lines and out in the sea. I am getting the same issues - on gear it can rev up to 2300 now (problem is getting worse) and then black water and smoke start to come out from exhaust. The max revs I am managing to get on load is 2400rpm (with full throttle).

Due to black water coming out - I have read it is unburned (excess) fuel.

Thanks

[Compass790]

have you tried skipperpetes diagnostic frm post 35? That should be your next step.

I'm assuming you have no gearbox or propshaft issues,apologies if i mentioned this before but just skimmed earlier posts.


Yes the smoke is unburned fuel

[Jesgatt]

Originally Posted by Compass790

have you tried skipperpetes diagnostic frm post 35? That should be your next step.

I'm assuming you have no gearbox or propshaft issues,apologies if i mentioned this before but just skimmed earlier posts.


Yes the smoke is unburned fuel

Hi, re post 35 - When the mechanic came he did as follows:
he run the engine and then started to loosen the fuel intake of each injector. When loose and diesel was not fed to it, the engine started to loose power - that is why he assumed that both cylinders are working. He also tried a compression test on each cylinder and they gave the same results (around 400 psi). This procedure was done on idle. We also run the engine at around 1500 rpm on the mooring lines - the revs remains constant on load, however the engine will smoke. The tacho works fine (off load I put the engine to gas down and got around 3850 rpm). Re injectors - i took them for a service twice in about 3 months, first time they serviced them and 2nd time they replaced the injector head.
I have not seen any evident issues with the gearbox, prop and hull.

My issue is not revs dropping out but on load the rpm increase steadily, but the max rpm attained is that of 2200. Re the exhaust manifold - i checked the elbow and replaced the exhaust pipe (checked the water lock and manifold too)

Hope this helps
Jes

[Compass790]

Originally Posted by Jesgatt

Hi, re post 35 - When the mechanic came he did as follows:
he run the engine and then started to loosen the fuel intake of each injector. When loose and diesel was not fed to it, the engine started to loose power - that is why he assumed that both cylinders are working. He also tried a compression test on each cylinder and they gave the same results (around 400 psi). This procedure was done on idle. We also run the engine at around 1500 rpm on the mooring lines - the revs remains constant on load, however the engine will smoke. The tacho works fine (off load I put the engine to gas down and got around 3850 rpm). Re injectors - i took them for a service twice in about 3 months, first time they serviced them and 2nd time they replaced the injector head.
I have not seen any evident issues with the gearbox, prop and hull.

My issue is not revs dropping out but on load the rpm increase steadily, but the max rpm attained is that of 2200. Re the exhaust manifold - i checked the elbow and replaced the exhaust pipe (checked the water lock and manifold too)

Hope this helps
Jes

Did he loosen each injector pipe whilst it was running at 1500 rpm whilst tied to dock & see if the rev drop was the same for ea. cylinder?
I would check the injection timing now as you are running out of diagnostic checks.
Engine alignment ok? There are youtube vids on that. Stuffing box not getting hot?
You have checked air intake/exhaust are clear & valves working ok which I thought was most likely apart from injectors.
Sorry but I'm baffled now. I'm intrigued as to what it will turn out to be.
Good luck with finding the problem & please report back if you do.

[Jesgatt]

Originally Posted by Compass790

Did he loosen each injector pipe whilst it was running at 1500 rpm whilst tied to dock & see if the rev drop was the same for ea. cylinder?
I would check the injection timing now as you are running out of diagnostic checks.
Engine alignment ok? There are youtube vids on that. Stuffing box not getting hot?
You have checked air intake/exhaust are clear & valves working ok which I thought was most likely apart from injectors.
Sorry but I'm baffled now. I'm intrigued as to what it will turn out to be.
Good luck with finding the problem & please report back if you do.

Hi,
Problem seems to be partially solved. I had a blocked diesel return pipe. At the time being I am seeing 2400 rpm on load and no black water out. Still need to service diesel pump.

Thanks

[Compass790]

Originally Posted by Jesgatt

Hi,
Problem seems to be partially solved. I had a blocked diesel return pipe. At the time being I am seeing 2400 rpm on load and no black water out. Still need to service diesel pump.

Thanks

Thanks a lot for reporting back, I am intrigued by your problem, never would have guessed about blocked rtn pipe as that should be getting only filtered fuel thru it.
Do you know what blocked it & what pointed you to find that fault?
When you say service diesel pump are you talking lift pump or injector pump?
i'm in lockdown so plenty of time to follow threads but understand if you are busy.