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Discussion Starter · #1 ·
I have a Yanmar YSB-12. While motoring overnight, my sailing partner inadvertently turned off the ignition key. The motor continued running fine (about 6 hours). When we pulled it back to idle it died and since the key was off the alternator was off line and the batteries were dead.

Since then the engine will start but soot appears in the exhaust (no smoke, just black in the water) and the engine won't get above idle and then dies (30 seconds to a minute or so).

I have bled the system: same symptom.
I have pumped out all fuel and cleaned the tank: same symptom.
I have replaced the fuel filter and lines: same symptom.
I have pulled the intake: it is clear and with it removed, same symptom.
I have pulled the exhaust: it is clear and with it removed, same symptom (but loud).
I have pulled the injector, stripped and cleaned it, installed it outside of the engine and when cranking, I get a very good atomized puff of fuel. Reinstall: same symptom.

Any ideas? Is it just a coincidence that it failed after running with the key off? Did not having the fuel pump running cause something to fail. I am at my wits end!

Anyone know a diesel mechanic I can hire in Southern California? My boat is in Dana Point.
 

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Check your alternator. Don't see how that should keep a diesel from running,
but that is all that i can see this damaging. Does the system have an electric engine shut of switch?
 

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Discussion Starter · #3 ·
No problems with battery or alternator. I keep the batteries on a charger and the engine cranks and fires first-time-every-time. Then it chugs for a while and dies. All the while putting out black soot on the water.

I was thinking without the electric fuel pump running, the injector pump may have been working "harder" than normal. Maybe it is damaged. But like I said, the injector puffs a nice atomized puff of fuel. Of course, I have no idea what it should look like but it seems good to me.
 

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Perhaps you have damaged the alternator and it is now providing too much physical resistance somehow, the engine will fire and idle, but as soon as you try to rev it up, the load is too much which gives you the soot (which is probably unburnt fuel rather than soot). I can't see how anything else could have been damaged by having no power to the engine. I don't know the YSB, but if the belt only drives the alternator and not anything else, try taking the belt off and seeing if the engine will run better. Obviously if the belt does drive something else, like the water pump, then don't do this!
 

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If you have an electric fuel (engine) shut down, then you have a solenoid that does that for you when you push the kill switch, either by opening on starting or closing. On my Perkins the engine will run w/o the key on (not start) but will not shut down. Perhaps this solenoid has gotten weak and does not engage or disengage completely. It is connected to the fuel distribution pump, so it might be allowing this pump to only pass some fuel, but not enough to operate properly, or too much.
 

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Discussion Starter · #8 ·
The electric pump seems ok. I can turn on the key and when I open the bleed valve at the injector pump fuel comes out. Perhaps the pressure is low?

I don't think the Yanmar YSB12 uses a shutoff solenoid but to be honest, I don't know for sure. I will look into that. Although it seems if that was a problem it wouldn't start at all.

The belt on the alternator doesn't slip and the alternator doesn't make any noise so that seems ok.

Is there anyway to test the injector pump? My fear is that it isn't something simple but is a cracked cylinder, cracked water jacket, or blown head gasket but I don't know if that fits the symptoms.
 

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Sorry, I don't know that particular diesel at all. Any of those things could show up as water in the oil which I assume you have checked, or bubbles in the expansion tank on a fresh water cooled engine. Bad rings could cause the soot or smoke, high crank case pressure and low power. But none of these things should be related to operating without the key being on, except that the alarms would not have functioned if it overheated, which could cause a cracked cylinder, a cracked water jacket, or a blown head gasket or even broken some rings. Sorry, let's hope not. You might want to do a compression test on the engine.
 
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It sounds like it is starved for fuel. Maybe rig a temporary fuel supply and see how it behaves. I am concerned that the 'key off' state disabled engine alarms and you would not have known about overtemp or low oil pressure but the symptoms don't seem to match (to me).

Is there a strainer or screen on the tank fuel pickup?
 

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Black smoke (although you say soot, not smoke) is a sign of improper fuel/air mix. I would check air intake and filter first, as its easy to do, but not often the problem. The filter itself would need to be crazy dirty. Fuel pump pressure might be the problem, but again, its not common and more likely to just not work at all.

The most likely cause is dirty injectors. How long since they've been professionally cleaned? There is no way a novice could diagnose the proper atomization by just looking at it. They also can't be cleaned properly by just scrapping off the exterior soot. Personally, I would just buy a new one (its a single lung diesel right?), then have the old one cleaned and inspected as a spare (store it in diesel fuel).

Cracked heads, blown gaskets, etc usually add a few other telltales, such as water in the oil or exterior seeping on the motor itself. Blown rings will let oil past and one would expect some blue exhaust.

Leaving the ignition off seems coincidental, so far.
 
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I don’t know if it is related to the key being turned off, but I’m pretty sure I know what’s causing the black stain in the water. I think that the raw water input in the exhaust elbow was clogged. Pretty simple fix. Remove the exhaust elbow from the engine, unscrew the small adapter that introduces the raw water, and I think you’ll find the opening at least partially clogged with carbon like soot. Cleanup carbon buildup, reassemble, you should be good to go.
 

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The back pressure from a clogged elbow is a smoke causing issue, but I read that the OP already checked this. Maybe that's not what they meant by:

I have pulled the exhaust: it is clear and with it removed, same symptom (but loud).
 

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Discussion Starter · #14 ·
It is not a clogged or restricted intake. There is no filter, just a pipe. I have removed it, exposing the intake valve and started it. It died with the same symptom.

It is not a restricted exhaust. I removed the riser, exposing the exhaust valve and started it. It died with the same symptom.

I have bypassed the fuel pick-up in the fuel tank by running a line from the primary filter directly into the tank through an access plate. It died with the same symptom.

The point about no alarms is valid. I did notice that the oil level was low. The oil is black with no evidence of water. I removed the oil pressure sender and turned it over to make sure the oil pump was working. It is.

I did a full tear-down and cleaning of the injector, but as was mentioned, I probably can't judge the spray pattern.

I continue to hope it is a fuel problem and not something more severe in the engine. Maybe the injector pump?

The black soot really bothers me. I don't see how it jives with the symptoms unless it is because it isn't coming up to temperature or ????

Thanks for the help, I think you can see why my forehead is black-and-blue (the wall is getting dents).
 

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......The black soot really bothers me. I don't see how it jives with the symptoms unless it is because it isn't coming up to temperature or ????.....
Black is fuel/air mixture, poor combustion. Temp can cause tolerances to close up as metals expand, but not likely to cause black. More likely, blue (oil)

Let's bet a beer, it's your injectors. How many engine hours since the last professional cleaning? You many not take the bet, if you know. :)
 

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Injector service is a bit of a specialty. If you've torn it down yourself you may need it professionally checked. A proper pressure "pop" test will tell the tale better than a mere observation.

Another concern is that your alternator may be toast after having run so long with the key off.

Since the engine ran fine for hours after the key was turned off it's a little hard to believe that that has caused this new issue.
 

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I think you can see why my forehead is black-and-blue (the wall is getting dents).
I think you've done a fair bit! :) Pity the wall.

As I know nothing much about engines all I can give is a general bit of advice that seems to apply to all my boat problems: Go back to basics and think through the most likely things that occur when one turns the key off..

For example why is the key being off going to affect the air intake pipe? It can't.

The key being off affects electrical stuff, doesn't it? So whats the electrical stuff that could have failed as a direct cause of too much or too little electricity? Only the alternators, electric fuel pumps or other electrics that make the thing go (or stop).

I did like Paulinvictorias
Perhaps you have damaged the alternator and it is now providing too much physical resistance somehow,
Did you take the fan belt off and give it a spin?

Theres gotta be a direct cause, one problem doesn't jump left field, it can't. Can it?
Does your engine have an electronic EGR valve? Is that the sort of thing that could have overloaded? That makes smoke.


Mark
 

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Except for the black soot, it sounds like there may still be an air pocket or air leak somewhere in the fuel system. Your electric pump may be used to pressurize the system right up to the injector pump to bleed or pressurize, depending on the configuration. Maybe the pump's pressure is failing? Sounds like you did all the easiest things first before tearing it apart, maybe a repeat.

Can't think of anything but the alternator being effected by turning the key off unless there is some interface between the oil pressure, fuel pump, or alternator?

Paul T
 

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Take the belt off the alternator and see if it spins OK, since the engine ran at higher rpms and died when you went to idle maybe the alternator is binding just enough to stall out the engine at idle.

If not my bet is a piston problem and you are getting oil into your cylinder and that is maybe why the oil level is low and also why you are not getting a good burn, test the compression.
 

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Discussion Starter · #20 ·
I'm not sure I would bet it is the injector (it may be) but I think I would bet it is fuel related.

How is this for a theory: when the key was off, the electric fuel pump was off. With the fuel pump off the injector pump had to suck rather than being fed fuel. This may have caused some problems in the pump (perhaps the fuel cavitated during the suck allowing some scoring on the piston).

OR

Pulling fuel through the fuel pump somehow damaged it (seems less likely).

Here is what I will try this weekend:
1) Pull the alternator belt
2) Purchase a new electric fuel pump and rig it to pump from a clean can of diesel directly into the injector pump. That way, I bypass the filters and all lines up to the injector pump.

How does that sound? Any other experiments to narrow it down?
 
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