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Old 04-06-2012, 05:54   #1
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120 Lehman Black Smoke

Hey Guys;
I have a 36' Grand Banks Type (custom built) trawler hull cabin cruiser.
It has twin Ford Lehman 120 Diesels.
The port engine runs clean.The starboard engine blows black smoke.
If I run it at half throttle it runs clean.It cranks & runs great other than the smoke.
I had the injectors rebuilt-no change.
I tried running it without the air filter-no change.
Both engines have the same size props.
Any suggestions?
Thanks;
Mike
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Old 04-06-2012, 06:03   #2
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Re: 120 Lehman Black Smoke

Strip the exhaust elbow at the engine see if it is corroded or blocked also if you can check to see if the flexible exhaust pipes are partially blocked or de-laminating internally
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Old 04-06-2012, 06:13   #3
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Re: 120 Lehman Black Smoke

Thanks I,ll check it out.
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Old 04-06-2012, 11:14   #4
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Re: 120 Lehman Black Smoke

Mike, Black Smoke is probably not cause by your exhaust elbow. Typically it comes from unburned fuel. The problem could be with the injector pump since you have new injectors. It can also be caused by issues with the cylinder head, sticking or worn rings, or valves. It can also be the result of bad fuel, low compression, or excessive carbon build up, OK maybe in it will show in the exhaust elbow. My point is that unless you have the expertise, having a qualified mechanic check the engine might be the best way to go. Chuck
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Old 04-06-2012, 17:51   #5
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Re: 120 Lehman Black Smoke

Thanks.
That is a lot to consider.
One clue I forgot about is , that this is the side that I have had a problem with condensation.A few years back & about 4 months ago after sitting a few months without use ,the fuel/water separators (both primary & secondary) were full of water.They had to be drained,filled with diesel & primed.It is difficult to prime it also.That never happens on the port side engine.On the port side I can empty the separators(finding no water in them) & pour some fuel back into them & crank it & go without any priming.
Does this clue help?
Thanks;
Mike
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Old 04-06-2012, 18:03   #6
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Re: 120 Lehman Black Smoke

That's just something to factor in but the bottom line is that it could be any one of a number of things. Chuck
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Old 04-06-2012, 18:06   #7
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Re: 120 Lehman Black Smoke

I think its time to hire a professional who can diagnose the problem first hand. There are too many possibilities to make a distant guess at it.
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Old 04-06-2012, 18:41   #8
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Re: 120 Lehman Black Smoke

Black smoke / unburnt fuel most certainly could be caused by an exhaust restriction. That's a cheap thing to rule out before you go looking for more complicated explanations.
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Old 05-06-2012, 04:45   #9
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Re: 120 Lehman Black Smoke

G'day Mike,
Remember do the easiest and cheapest things first.
#1. Clean fuel lift pump filter screen.
# 2. Replace fuel filter elements, while you have filters out of system blow delivery line out.
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Old 05-06-2012, 05:24   #10
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Re: 120 Lehman Black Smoke

Hey Guys;
Thanks for all the input.
Plan to go check out some of the simpler things in the next few days.
I'll appreciate all the info I can get.
Thanks;
Mike
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Old 05-06-2012, 05:40   #11
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Re: 120 Lehman Black Smoke

Quote:
Originally Posted by fiberform View Post
Thanks.
That is a lot to consider.
One clue I forgot about is , that this is the side that I have had a problem with condensation.A few years back & about 4 months ago after sitting a few months without use ,the fuel/water separators (both primary & secondary) were full of water.They had to be drained,filled with diesel & primed.It is difficult to prime it also.That never happens on the port side engine.On the port side I can empty the separators(finding no water in them) & pour some fuel back into them & crank it & go without any priming.
Does this clue help?
Thanks;
Mike
Do you have separate tanks?
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Old 05-06-2012, 06:09   #12
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Re: 120 Lehman Black Smoke

Quote:
Originally Posted by Waterwayguy View Post
Mike, Black Smoke is probably not cause
by your exhaust elbow. Typically it comes from unburned fuel. The
problem could be with the injector pump since you have new injectors. It can also be caused by issues with the cylinder head, sticking or worn rings, or valves. It can also be the result of bad fuel, low compression, or excessive carbon build up, OK maybe in it will show in the exhaust elbow. My point is that unless you have the expertise, having a qualified mechanic check the engine might be the best way to go. Chuck
Speaking from very costly experience the mechanic you suggest wont now unless he strips the engine because there are to many variables. Then with your engine in bits you are in his hands. If you think advice is sensible and you have not thought of it then do it yourself keeping a log.

Just like you can examine an animal's poo to get an idea of its health, you can pay attention to the quality of your engine exhaust to get an idea of what's going on inside the engine. As the engine burns fuel and creates exhaust, lots of different things are happening. Unfortunately some of these things aren't supposed to happen. Things like burning oil, evaporating coolant and leaving unburned fuel in the exhaust -- these are not good to see.

Pay attention to what's coming out and you can get a good idea as to what problems your engine may be having, often before they get bad. This saves you money.

Black smoke from the exhaust. You notice black smoke coming from the exhaust when you start your engine. The smoke may or may not disappear after the engine is warmed. If it is, it is less noticeable. Engine may or may not be running rough or misfiring.

If you have a carburetor, the carburetor choke may be stuck closed. Diesels no Carburettor
The Fix: Repair or replace choke.
Fuel injectors may be leaking.
The Fix: Replace fuel injectors.
You may have a dirty air filter: Replace the air filter.
There may be some other type of ignition problem.
The Fix: Check distributor cap and rotor. Ignition module may be bad.

If a Diesel Engine
Diesel engines can produce black soot (or more specifically diesel
particulate matter) from their exhaust. The black smoke consists of carbon compounds that were not combusted, because of local low temperatures where the fuel is not fully atomized.

These local low temperatures occur at the cylinder walls, and at the outside of large droplets of fuel. At these areas where it is relatively cold, the mixture is rich (contrary to the overall mixture which is lean). The rich mixture has less air to burn and some of the fuel turns into a carbon deposit.

Modern car engines use a diesel particulate filter (DPF) to capture carbon particles and then intermittently burn them using extra fuel injected directly into the filter. This prevents carbon buildup at the expense of wasting a small quantity of fuel.

The full load limit of a diesel engine in normal service is defined by the "black smoke limit", beyond which point the fuel cannot be completely combusted. As the "black smoke limit" is still considerably lean of stoichiometric, it is possible to obtain more power by exceeding it, but the resultant inefficient combustion means that the extra power comes at the price of reduced combustion efficiency, high fuel consumption and dense
clouds of smoke. This is only done in specialized applications
(such as tractor pulling competitions) where these disadvantages are of little concern.

When starting from cold, the engine's combustion efficiency is reduced because the cold engine block draws heat out of the cylinder in the compression stroke. The result is that fuel is not combusted fully, resulting in blue and white smoke and lower power outputs until the engine has
warmed.

This is especially the case with indirect injection engines, which are less thermally efficient. With electronic injection, the timing and length of the injection sequence can be altered to compensate for this.

Older engines with mechanical injection can have mechanical and hydraulic governor control to alter the timing, and multi-phase electrically controlled glow plugs, that stay on for a period after start-up to ensure clean combustion—the plugs are automatically switched to a lower power to prevent their burning out.

Particles of the size normally called PM10 (particles of 10 micrometres or smaller) have been implicated in health problems, especially in cities. Some modern diesel engines feature diesel particulate filters, which catch the black soot and when saturated are automatically regenerated by burning the particles.

All diesel engine exhaust emissions can be significantly reduced
by using biodiesel fuel. (Possibly)
Effect of engine lubricating oil
The volatile component of 95% of diesel nanoparticles is unburned lubricating oil.
Forgot to ask you did you replace the injectors yourself or professionally do you have an air leak at the injectors.
Bit long winded Sorry!!
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Old 05-06-2012, 07:00   #13
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Re: 120 Lehman Black Smoke

Greetings and welcome aboard the CF, Mike.

Black smoke generally indicates poor and/or incomplete combustion of the diesel fuel. You seem to have eliminated many possible causes, excepting (perhaps):
Incorrect valve clearance
Low cylinder compression (eg sticking piston rings or worn components)
Excessive carbon build up in combustion and exhaust spaces
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