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Old 06-08-2008, 11:59   #1
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Unhappy Black Smoke Yanmar 2GM20

I’m at my wits end in working through a loss of power and “black” smoke issue with a Yanmar 2GM20 marine diesel on my 1996 Hunter 29.5. These symptoms suddenly showed up several weeks back. I suspected a dirty fuel tank and/or problems with the fuel. Drained the tank and then removed and cleaned the tank. Found debris in the supply tube elbow that restricted fuel flow. Replaced both the primary and secondary filters. Found little or no contamination in either. Returned the diesel fuel through a new West Marine water separator funnel. Bled the entire system. Final got enough pressure for the injectors and the engine started. I was able to idle, but still had an issue with power loss over 1700 rpm accompanied with black smoke. Decided to run Seafoam diesel treatment additive with a 1 to 1 mix via a bucket for several hours to clean the internals. This seemed to do the job. Ran engine through the entire range in neutral from idle to 3,200 rpm with no problems.

Took the boat out to test under load and ran between 1,500, and 3,000 for over an hour with no problem. I assumed all was well. Went out a couple of times and ran a total of 4-5 hours before the symptoms returned. Loss power and rpm’s at 2,200 rpm and the return of black smoke. Shut the engine down and sailed back to the slip.

Rechecked both filters and all looked good. Engine started fine but bogged down at about 1,800 rpm with the same old black smoke. Checked pump pressure via secondary bleed and had good pressure while idling. Removed and cleaned air filter. Checked mixing elbow and exhaust hose for debris and found none. Water flow and temperature from exhaust normal. Although, I noticed diesel fuel mixed with black suet floating on the water when engine would start to lose rpm’s and black smoke reappeared. Made sure both fuel tank vent and return lines were clear. Started right up again with the same problems.

Decided to pull and check injectors. Took to a local diesel shop and both pressure and spray appeared normal. Replaced, bled, and restarted with the same symptoms. Starts up on first crank fine. Can idle at 1,000 rpm for 10-15 minutes then bogs down with drop in rpm’s and the return of black smoke; or when I try to increase to 2,000 the rpm’s drop off and engine goes to a stall as the black smoke reappears.

Not sure what to check next. Any and all suggestions welcomed.
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Old 06-08-2008, 12:06   #2
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a local old mechani, would say diesel must have black smoke; usually black smoke is a sign of trouble in piston rings, turbo charger or even injection pump => last 2 -> big bucks

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Old 06-08-2008, 13:52   #3
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No black smoke is not a sign of a ring problem. Black smoke is a sign of poorly burn't fuel from not enough air, which can be caused by several problems.
First question, how dirty is prop and hull??
Fuel issues will not cause the problem of black. It will cause loss of power however.
A faulty turbo can cause this issue, but I don't read anywhere that this is a turbo'd engine.
Nor will an IP cause black smoke, unless the rack setting ha been played with and too much fuel is being pumped.
Quote:
Checked pump pressure via secondary bleed and had good pressure while idling.
That has me completely confused. How can you check pump pressure via "secondary bleed"??? whatever that is. If you did manage to check the pump pressure how would you know what pressure it has to be, to be correct.
Go to the Study Hall and take a look through some of the info there.
In general when you have black smoke, follow the following steps. and this is assuming that the engine/prop used to be just fine.
Check prop and hull for fouling.
Check air filter
Check exhaust
Check injectors by having them tested
Check injector pump for adjustment
Check injector pump by bench testing
All in that order and ensure injectors and IP are checked and tested by a professional.
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Old 06-08-2008, 17:43   #4
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Black smoke is fuel.
Go IN THE ORDER that Alan laid out
When was the last time the boat was hauled?
Where are you?
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Old 06-08-2008, 18:10   #5
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this calls for a compression test and leakdown.
I'm guessing this engine was loved to death.
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Old 06-08-2008, 18:47   #6
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I'm rebuilding a 1986 Vetus 4.14. Let me tell you, that I was up to my ears in rebuild manuals, USN training manuals, online forums, and receiving advice from just about every farmer slash diesel mechanic in the area. It took awhile to get enough grounding in the art of diesel mechanics to reasonably disassemble my motor. Luckly I had scale in the washdown side of the manifold, and corrosion problems galore. A simple rebuild was all that I needed, plus the cast iron washdown jacket. Popped everything out, and it's at the machine shop.

Definitely you have a non fuel or maintenance related problem that requires testing equipment. The spray test was fine, getting further into the injection system, the injector pump might be the problem. My understanding is that the pump itself has parts that go bad. There's a spring, throttle plate, and rings that changes fuel levels as the rpms rise. That sounds like what you got, but I don't have the experience to be sure. The diesel shop can tell you. BTW, Sometimes you get bad advice. Been there done that here, that's for sure. For example, I picked the wrong barber today. What a mistake.
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Old 06-08-2008, 18:58   #7
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Originally Posted by usa-068 View Post
getting further into the injection system, the injector pump might be the problem. My understanding is that the pump itself has parts that go bad. There's a spring, throttle plate, and rings that changes fuel levels as the rpms rise.
not in the pump used in the GM series. If the rack moves freely and your getting good fuel to the injectors. More often than not it's within or near spec.
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Old 06-08-2008, 19:29   #8
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Quote:
Originally Posted by never monday View Post
not in the pump used in the GM series. If the rack moves freely and your getting good fuel to the injectors. More often than not it's within or near spec.

Exactly what I was trying to say. As an untrained mechanic, sometime you get good advice, sometimes you don't. What happened was JMD checked out the injectors, any shop will do that for you. What the shop isn't saying is that the customer was willy nilly. Those dollars spent at the shop could have been spent on a mechanic to come out to the boat. The compression/drawdown tests could have been done at that time, instead of the injector test, and the problem more adequately and thoroughly addressed. Do it yourself spirit, along with a devotion to pride won't let some diesel engine owners open up the checkbook, or even to purchase a few books and manuals.

Luckly in my case the big hole in the washdown was a clear giveaway, any self trained mechanic could have figured out white smoke, saltwater corrosion, and oreo cookie sized carbon chunks.
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Old 07-08-2008, 06:13   #9
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Here’s a few earlier CF discussions on “Black Smoke”:
black smoke - Google Search
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Old 07-08-2008, 11:43   #10
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Exhaust elbows are a regular cause of blsck smoke..

Check out this site, they have a bunch of very knowledgable people hanging around........m


Yanmarhelp.com Message Forum - Yanmar marine diesel engine help & advice (Powered by Invision Power Board)&
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Old 07-08-2008, 11:57   #11
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A couple of people have posted that site but my internet connection always times out before it loads and we have a pretty fast connection.
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Old 09-09-2008, 10:00   #12
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MIxing elbow

Quote:
Originally Posted by jmdezzutto View Post
I’m at my wits end in working through a loss of power and “black” smoke issue with a Yanmar 2GM20 marine diesel on my 1996 Hunter 29.5. These symptoms suddenly showed up several weeks back. I suspected a dirty fuel tank and/or problems with the fuel. Drained the tank and then removed and cleaned the tank. Found debris in the supply tube elbow that restricted fuel flow. Replaced both the primary and secondary filters. Found little or no contamination in either. Returned the diesel fuel through a new West Marine water separator funnel. Bled the entire system. Final got enough pressure for the injectors and the engine started. I was able to idle, but still had an issue with power loss over 1700 rpm accompanied with black smoke. Decided to run Seafoam diesel treatment additive with a 1 to 1 mix via a bucket for several hours to clean the internals. This seemed to do the job. Ran engine through the entire range in neutral from idle to 3,200 rpm with no problems.

Took the boat out to test under load and ran between 1,500, and 3,000 for over an hour with no problem. I assumed all was well. Went out a couple of times and ran a total of 4-5 hours before the symptoms returned. Loss power and rpm’s at 2,200 rpm and the return of black smoke. Shut the engine down and sailed back to the slip.

Rechecked both filters and all looked good. Engine started fine but bogged down at about 1,800 rpm with the same old black smoke. Checked pump pressure via secondary bleed and had good pressure while idling. Removed and cleaned air filter. Checked mixing elbow and exhaust hose for debris and found none. Water flow and temperature from exhaust normal. Although, I noticed diesel fuel mixed with black suet floating on the water when engine would start to lose rpm’s and black smoke reappeared. Made sure both fuel tank vent and return lines were clear. Started right up again with the same problems.

Decided to pull and check injectors. Took to a local diesel shop and both pressure and spray appeared normal. Replaced, bled, and restarted with the same symptoms. Starts up on first crank fine. Can idle at 1,000 rpm for 10-15 minutes then bogs down with drop in rpm’s and the return of black smoke; or when I try to increase to 2,000 the rpm’s drop off and engine goes to a stall as the black smoke reappears.

Not sure what to check next. Any and all suggestions welcomed.
I have had a similar problem with a Yanmar 2GM20 installed 2002, with 300 hours on the clock, now diagnosed as a complete break in the weld which connects the exhaust pipe within the cooling water extract pipe, allowing water to enter the engine and cause damage, as yet unquantified. The mixing elbow is a curved steel pipe attached to the engine which allows the exhaust gases to leave the engine concentric within the cooling water extract pipe. The exhaust pipe is (or should be) welded to the flange connecting to the engine block, thus denying cooling water access to the engine interior. It bloooks like big money repairs, and an argument with Yanmar
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Old 12-06-2009, 22:30   #13
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The link to the Yanmar site is no good.

Can a bad cooling elbow cause black smoke decreased rpm under load?
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Old 12-06-2009, 23:58   #14
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I'am just a dumb backyard mechanic but I am intriged by:

"Can idle at 1,000 rpm for 10-15 minutes then bogs down with drop in rpm’s and the return of black smoke; or when I try to increase to 2,000 the rpm’s drop off and engine goes to a stall as the black smoke reappears."
"I noticed diesel fuel mixed with black suet floating on the water when engine would start to lose rpm’s and black smoke reappeared."

1. Black smoke indicates high load (high fuel to air ratio).
2. Drop in RPM, lack of power and subsequent stalling usually means no fuel or a blocked air intake (to stall it has to be completely sealed off, not just constricted)
3. Oil in the exhaust means unburned fuel, the soot is most likely being washed out of the exhaust manifold etc. by the oil.

Items 1. and 2. are contradictory. Item 3 reinforces #1.
This can only mean some sort of timing issue. My quess is the fuel is being injected to late in the stroke. There is not enough pressure and time to fully burn the fuel.
Remember that:
1. a diesel uses pressure to ignite the fuel. The higher the compression the higher the temperature.
2. the timing of the fuel delivery is critical for proper ignition and subsequent burning.
3. diesel is an oil, the injectors spray droplets which need heat(pressure) to ignite and then time to burn , it does not vapourise like gasoline.

If the oil is injected to late the droplets will not burn properly giving you a lot of black smoke(partially burned oil) and oil in the exhaust.
There would be a reduction in power as obviously the increase in pressure from inefficient burning occurs too late in the power stroke.

Solution:
You need a diesel mechanic to check the timing of the injection. This usually means a visit to your boat. For some reason something has slipped out of adjustment.
That was my thoughts, I hope it helps.

PS. I feel sorry for your exhaust valves.
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Old 13-06-2009, 05:18   #15
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2GM20F smoking

I just went through the same thing with my 2GM20F. It took almost a year, a couple of sets of injectors and several mechanics until I found one who knew what he was doing.

The bottom line was that the injector pump needed rebuilding. The pump had been checked by a qualified shop but they said it was fine. The mechanic that solved it pulled the injector pump did his own rack test and pronounced it bad.

Pump rebuilt, no more problems.

Good luck.... MikeF
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