Mep 831a black smoke won't rev up and shooting flames out the exhaust

[Captainscall]

Sorry to hear that you are still having issues. I feel your pain. As I mentioned earlier, I had a basically unnoticeable air leak on the inlet to the IP that gave me very similar overfueling grief. And, yes, I was pulling my hair out trying to figure out what the issue was, too. The only fix was to replace the pump as it was a crack on the pump itself.

Replacing the IP is straightforward, just follow the procedure and make sure that the governor yoke engages the IP pin.

When you checked the valve clearances, did you check for a bent tappet.) Have you checked that the timing is approximately right, and the correct valves are opening?
(I knew someone who had a Yanmar that the prior owner had put in a starter that was the wrong starter model and it was spinning the engine backwards. It didn't run very well, but it did run... Apparently, Yanmar makes a CW and a CCW starter for different engine versions.)

All the best,

2Pbfeet

Thanks for the info. If it is an air leak it’s gonna be hard to find. There are no fuel leaks or seepage that I can find. I have not checked the timing yet and did not look for a bent tappet.


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[Captainscall]

Dumb question, but are you sure that the intake is completely open and there isn't something whacko like shop rag or something stuck in the intake?

I pulled off the air filter housing and looked into the intake heater and everything appears clear. I did not remove the intake heater


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[2Pbfeet]

I pulled off the air filter housing and looked into the intake heater and everything appears clear. I did not remove the intake heater


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I'm just grasping at straws for what else might be causing overfueling / reduced air.

Generally, these are simple, rock solid engines, so when you get it running, it ought to be very reliable.

All the best,

2Pbfeet

 

[CallMeColt]

If you want to toss an injection pump at it, let me know. I have two of them here. The used, known good one I won't sell for to much more than a new China one.

 

[Captainscall]

If you want to toss an injection pump at it, let me know. I have two of them here. The used, known good one I won't sell for to much more than a new China one.

I am definitely going to look into the fuel side leading up to the injection pump. Might throw an injection pump on it too. I pumped all of the old fuel out of the tank using the low pressure pump. I did not notice any air bubbles except for if I shut the low pressure pump off then kicked it on I saw a few bubbles which I thought was weird but when the pump is on there are no bubbles.


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[Ray70]

I'd try replacing the pump.
I'm not sure how the internals of the Yanmar pumps are held together, but years ago I was working on a 701 which is a somewhat similar design and the engine was acting similar to your issue.
It turned out that the internals of the IP has gotten gummed up. The owner was able to forcefully free it up ( because the 701 governor linkage is external to the engine, but in the process, the internal fuel plunger slipped in relation to the adjustment pin and rack, causing it to be rotated about 180* out of whack.
The result of which was that whatever the governor was "trying to do" the engine would react the opposite!
governor wants less fuel... Engine gets more fuel!
And the harder the governor tried to reduce the fuel, the more the fuel got delivered!

 

[DieselAddict]

Nothing really "holds" them together. They are precision machined and don't even have any rubber seals inside. Makes sense since rubber would not survive the pressures.

You unscrew the top of the pump and the rest of the guts will come out (assuming its not gummed up). They are super simple and easy to clean if you need to do that. BUT do NOT use any abrasive material for cleaning. Use only solvents and towels. An ultrasonic cleaner is OK but NO scotchbright or other abrasive type materials. You will ruin the pump.

 

[2Pbfeet]

I'd try replacing the pump.
I'm not sure how the internals of the Yanmar pumps are held together, but years ago I was working on a 701 which is a somewhat similar design and the engine was acting similar to your issue.
It turned out that the internals of the IP has gotten gummed up. The owner was able to forcefully free it up ( because the 701 governor linkage is external to the engine, but in the process, the internal fuel plunger slipped in relation to the adjustment pin and rack, causing it to be rotated about 180* out of whack.
The result of which was that whatever the governor was "trying to do" the engine would react the opposite!
governor wants less fuel... Engine gets more fuel!
And the harder the governor tried to reduce the fuel, the more the fuel got delivered!

On these engines, the yoke (fork) on the governor might not be holding the adjustment pin on the pump, but that's about it. It is always worth checking the observation slot under the small plate below the pump to double check that the pin is in the fork. I know of others who have had the camshaft do bad things (e.g. shear, cam gear lose teeth), but those engines rarely manage to fire.

All the best,

2Pbfeet

 

[Captainscall]

Still racking my brain on what is causing the issue. Waiting for a new injection pump. Is there any chance that the gasket #2 in the photo of the injection pump would allow air in without leaking fuel? I did come across a video of one running just like mine did and the cause was overfilled oil. I went back and checked oil again per the manual. Did not thread the dipstick in and it was halfway between the marks on the dipstick.

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[2Pbfeet]

Still racking my brain on what is causing the issue. Waiting for a new injection pump. Is there any chance that the gasket #2 in the photo of the injection pump would allow air in without leaking fuel? I did come across a video of one running just like mine did and the cause was overfilled oil. I went back and checked oil again per the manual. Did not thread the dipstick in and it was halfway between the marks on the dipstick.

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I highly doubt it. Nice thought. That is on the mechanical side of the pump. If 17 were leaking and the pump internals were bad, perhaps, but then you would probably be getting fuel in your oil.

All the best,

2Pbfeet

 

[Captainscall]

I highly doubt it. Nice thought. That is on the mechanical side of the pump. If 17 were leaking and the pump internals were bad, perhaps, but then you would probably be getting fuel in your oil.

All the best,

2Pbfeet

Thanks for the input. I have minimal diesel experience so I am on a huge learning curve. I plan to install the injection pump. If that does not solve the problem I will check timing and probably replace the whole low pressure side of the fuel system. I did check the cam today and did not see or feel any unusual wear. I really think I have already checked or done everything except what is mentioned above.


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[FarmingSmallKubota]

while you wait why not go ahead and drain a little oil out. just try it and see what do you have to lose?

 

[Captainscall]

while you wait why not go ahead and drain a little oil out. just try it and see what do you have to lose?

Appreciate the suggestion! I think I will give it a try. Just afraid to run it too low I would assume if I brought the level down to the bottom of the dipstick it should still have enough oil to run safely.


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[2Pbfeet]

Thanks for the input. I have minimal diesel experience so I am on a huge learning curve. I plan to install the injection pump. If that does not solve the problem I will check timing and probably replace the whole low pressure side of the fuel system. I did check the cam today and did not see or feel any unusual wear. I really think I have already checked or done everything except what is mentioned above.


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While "When you have a hammer, every problem looks like a nail....", I do think that the issue sounds like an air leak or a bad IP. While you are waiting, I would replace as much of the low pressure line as you can, and while you do that, look for any dirt, hair, scratches, cracks, anything that might leak. Since you mentioned that you don't see any weeps or wet spots, I am leaning a bit towards the IP, but only slightly. Have you tried a fresh hose and fitting and directly feeding the IP?

Yanmar builds these engines to be used in some pretty poor conditions. There's an amusing (to me, at least) figure in a Yanmar manual about decanting diesel off of the water layer below. These aren't pampered Mercedes engines.

Oil half way down the dipstick will be fine.

All the best,

2Pbfeet

 

[FarmingSmallKubota]

Appreciate the suggestion! I think I will give it a try. Just afraid to run it too low I would assume if I brought the level down to the bottom of the dipstick it should still have enough oil to run safely.


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If you drain it that low the low oil sensor should shut it right back off. just half way will be fine. these things are as simple as they get.

 

[Captainscall]

While "When you have a hammer, every problem looks like a nail....", I do think that the issue sounds like an air leak or a bad IP. While you are waiting, I would replace as much of the low pressure line as you can, and while you do that, look for any dirt, hair, scratches, cracks, anything that might leak. Since you mentioned that you don't see any weeps or wet spots, I am leaning a bit towards the IP, but only slightly. Have you tried a fresh hose and fitting and directly feeding the IP?

Yanmar builds these engines to be used in some pretty poor conditions. There's an amusing (to me, at least) figure in a Yanmar manual about decanting diesel off of the water layer below. These aren't pampered Mercedes engines.

Oil half way down the dipstick will be fine.

All the best,

2Pbfeet

At this point with everything I have done and no change in how it runs I am also leaning towards air leak or IP. I have not bypassed with new lines so I will try that too while I wait. Thanks!!


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[2Pbfeet]

At this point with everything I have done and no change in how it runs I am also leaning towards air leak or IP. I have not bypassed with new lines so I will try that too while I wait. Thanks!!


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Bypassing the lines is a quick and dirty way to rule out a few things.

FWIW:

The three studs holding the pump on can't take a lot of torque. They need to be tight, but don't wail on them when you put together again.

All the best,

2Pbfeet

 

[2Pbfeet]

Have you ever seen it run without black smoke? I.e. could an oil seal be missing on a valve?

 

[CallMeColt]

I would have sold you a known good injection pump for $30. Yanmar. Hope you got a good deal.

Forgive me if some of this has been suggested, but gears are turning...

The low pressure side getting air would make it starve for fuel. I have run them with a hose pressed on & air definitely getting in. With the electric pump on the MEP 831A, it will just leak vs pull in air. Easiest way to eliminate anything in the low pressure side is to remove the fuel inlet & gravity feed a fuel line from a funnel.

Are you sure the electric pump is moving the proper amount of fuel?

Did you try running it with the electronic speed controller linkage removed so it will just run at 3600RPM? How about something like 1300 RPM? And use the manual knob to stop it? Be sure to remember where it is at before loosening so you can put it back.

Did you confirm all the springs are present & on the linkage are where they belong on the governor? There are quite a few. TM will tell you the right holes to be in. This would all be behind the black knob area.

 

[KN6KXR]

Years ago I had an issue with a Kubota 1.5l 3-cyl diesel genset. Those motors are legendarily indestructible. So it was missing and spitting and blowing diesel and would run OK then stutter..... After doing a bunch of fuel related stuff I finally pulled the unit off the mountain location and back to the shop for a tear down. It belonged to a bunch of hippy kids growing dope. Stuff is legal here and what do I care I don't smoke it I just fix stuff for a living.... Anyways I never did get a good story of what happened until I took it apart.

Turns out at some point the idiots had way overfilled it with oil. This bent one of the rods. Hydrolocked it. Just one of the three. Then they corrected the level before I got there. It was plain as day when I put the rods next to each other one was crooked as hell. Actually I could tell right away when I took the head off, rotated the motor, and you could see one of the pistons didn't rise as far as the others. I still have it kicking around the shop as a story piece. Guess those kids were smoking too much of their stuff while trying to do their PM's!

So I put a new rod in, then took the leads as spec, and it ran like new. If I was you I would go ahead and pull the head and squish some lead. Sounds like inadequate compression could be on the menu.