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

[Captainscall]

Hi All,

This is my first post. My new to me MEP 831A has me stumped. It starts quick even in the cold. But it billows tons of black smoke, the governor arm has to stay WOT just to keep it running. After 2 min or so the muffler glows orange and backfires really loud with flames out the exhaust. Which at that point I usually shut it down.

So far it has new batteries, filled with fresh fuel and verified it has good flow to the injection pump. I went ahead and disassembled the injection pump cleaned it and reinstalled it. I pulled the injector with the fuel lines still attached and cranked the engine just to see the spray pattern. Injector visually looks like it is working fine. I checked the intake and exhaust for restrictions and they look fine. Engine runs exactly the same after all of that.

At first i was hoping it was just a governor adjustment or speed controller but running the governor by hand i can tell it will only run if it is held wide open.

I will try and post a video but I am new at this.

Thanks for your help!!

 

[WWRD99]

Sounds like the injector is stuck open dumping fuel. With the black smoke and the red exhaust points to to much fuel. Could be the timing is way off too or both.

Sent from my SM-S906U using Tapatalk

 

[Captainscall]

Thanks for the reply. I was thinking the same thing about the injector being stuck open. Unfortunately I do not have the tools to test for that. I did not want to start throwing parts at this machine but I might just have to pick up a new injector. I will have to check the timing too.

Thanks!!

 

[WWRD99]

Slow down. Before you buy anything, test. Troubleshoot. KNOW what is wrong.

You could start the set, and let it run a tad. Then use a heat/temperature gun to look at each cylinder to read the temps, and see if one is hotter than the rest.

Or, you could pull an IP, (you have done that once and I hope you got it back in right) and leave it hooked up to the fuel system. Start the set. Look at the spray pattern. spray all the time? Or not. Do that to each cylinder.

Would be good to see a video.

There are several other reasons this might happen. But take it one step at a time.

Ok I'm confused. I thought the 831 had one cylinder. Is there another type out there? I have a 531 and thought the engines were similar.

Sent from my SM-S906U using Tapatalk

 

[Guyfang]

Your right. I was working on 803 sets tonight, and just did not read it right. So forget what I wrote!! Sorry.

 

[WWRD99]

Your right. I was working on 803 sets tonight, and just did not read it right. So forget what I wrote!! Sorry.

Never apologize bud!! I don't know these that well so it threw me off thinking there was a different model that was offered.

Sent from my SM-S906U using Tapatalk

 

[WWRD99]

Thanks for the reply. I was thinking the same thing about the injector being stuck open. Unfortunately I do not have the tools to test for that. I did not want to start throwing parts at this machine but I might just have to pick up a new injector. I will have to check the timing too.

Thanks!!

So my thought on testing the injector would be jump starting it with the nato plug, with the injector removed but with the metal line hooked up. Could get a see of what the injector is doing turning over fast. Could use the battery with a good jump pack on it too but thinking the faster it turns over the better. I'd go through the tm and make sure timing is spot on though too.

Sent from my SM-S906U using Tapatalk

 

[Captainscall]

So my thought on testing the injector would be jump starting it with the nato plug, with the injector removed but with the metal line hooked up. Could get a see of what the injector is doing turning over fast. Could use the battery with a good jump pack on it too but thinking the faster it turns over the better. I'd go through the tm and make sure timing is spot on though too.

Sent from my SM-S906U using Tapatalk

So I did as you described. Spray pattern looks good to my untrained eye. It was really hard to tell if it was leaking in between sprays but if I was a betting man I would say it dropped a little in between. Think I will go ahead and order an injector. I will update as soon as it gets here.

If anyone has any other ideas I am all ears. Would really like to get this one going!!

Thanks for all the input so far.


Sent from my iPhone using Tapatalk

 

[Captainscall]

Your right. I was working on 803 sets tonight, and just did not read it right. So forget what I wrote!! Sorry.

No worries. Hoping to get an 802 or 803 myself. Might need your help!!!! Thanks!!!


Sent from my iPhone using Tapatalk

 

[WWRD99]

So I did as you described. Spray pattern looks good to my untrained eye. It was really hard to tell if it was leaking in between sprays but if I was a betting man I would say it dropped a little in between. Think I will go ahead and order an injector. I will update as soon as it gets here.

If anyone has any other ideas I am all ears. Would really like to get this one going!!

Thanks for all the input so far.


Sent from my iPhone using Tapatalk

That sounds good. Sometimes the injector pintle gets pushed open with the engine compression too. The injector shouldn't cost much. You find a part number in the tm?

Sent from my SM-S906U using Tapatalk

 

[FarmingSmallKubota]

I had a similar experience with a 531 not too long ago, just for nailing things down pull the flash arrestor off of the end of the exhaust and see what happens

 

[Captainscall]

That sounds good. Sometimes the injector pintle gets pushed open with the engine compression too. The injector shouldn't cost much. You find a part number in the tm?

Sent from my SM-S906U using Tapatalk

I found out the engine is a yanmar l70ae. I looked up the part number for the engine then ordered the replacement. Hope to have it before Christmas.


Sent from my iPhone using Tapatalk

 

[Captainscall]

I had a similar experience with a 531 not too long ago, just for nailing things down pull the flash arrestor off of the end of the exhaust and see what happens

Oh that’s very smart. Never thought about a spark arrestor. I will definitely look into this one and get back with the results!!


Sent from my iPhone using Tapatalk

 

[2Pbfeet]

FWIW: Those l70/l100s are prone to overfueling if there is air getting into the fuel line. 90% of the time it is an air leak on the suction side, and the air leaks can be hard to find because it doesn't take much air to mess things up. I had one that turned out to be a hairline crack on a fuel solenoid. I don't recall how long it took to find, but I was pulling my hair out for sure.

The air keeps the injection pump from developing full pressure, so the fuel injector dribbles fuel over a longer time that does not ignite well, rather than a burst at TDC that burns completely. The lack of adequate combustion (rpm) causes the governor to advance more fuel making the problem worse.

All the best,

2Pbfeet

 

[Captainscall]

FWIW: Those l70/l100s are prone to overfueling if there is air getting into the fuel line. 90% of the time it is an air leak on the suction side, and the air leaks can be hard to find because it doesn't take much airs to mess things up. I had one that turned out to be a hairline crack on a fuel solenoid. I don't recall how long it took to find, but I was pulling my hair out for sure.

The air keeps the injection pump from developing full pressure, so the fuel injector dribbles fuel over a longer time that does not ignite well, rather than a burst at TDC that burns completely. The lack of adequate combustion (rpm) causes the governor to advance more fuel making the problem worse.

All the best,

2Pbfeet

Oh that’s a good one too. I took the fuel line that feeds the injection pump and put it in a glass. Ran the fuel pump and watched the flow. The fuel coming out of the line was solid and I saw no air bubbles. I assume that was the only way to check for air bubbles?

Thanks!!


Sent from my iPhone using Tapatalk

 

[2Pbfeet]

Oh that’s a good one too. I took the fuel line that feeds the injection pump and put it in a glass. Ran the fuel pump and watched the flow. The fuel coming out of the line was solid and I saw no air bubbles. I assume that was the only way to check for air bubbles?

Thanks!!


Sent from my iPhone using Tapatalk

That's a great first step, but there is still the connection at the end of that line (dirt, debris, scratch, etc.) for a possible site for a leak, and the pump itself.

For the unit that I mentioned above, there were no bubbles in that line, they were getting in just at the connection to the injection pump, still on the suction side. I would look closely for any sign of a diesel weep on the line. I use a rag, followed by a rag with acetone to get any residual oil/diesel off.

Have you loosened the plate on the injector pump to check that the pump pin is engaged properly in the governor rack?

If you haven't bled the high pressure line already, slightly loosen the fitting at the injector and crank the engine for a bit to bubble diesel out (use a rag), and then promptly tighten the fitting. A little bubble in the high pressure line can cause over-fueling as well. I think that the Yanmar engines are very solid reliable engines generally, but unlike some other diesels, they do have trouble clearing air in the high pressure line.

I think that the odds on bet is still a bad injector, if you have already bled the high pressure line.

All the best,

2Pbfeet

 

[Captainscall]

That's a great first step, but there is still the connection at the end of that line (dirt, debris, scratch, etc.) for a possible site for a leak, and the pump itself.

For the unit that I mentioned above, there were no bubbles in that line, they were getting in just at the connection to the injection pump, still on the suction side. I would look closely for any sign of a diesel weep on the line. I use a rag, followed by a rag with acetone to get any residual oil/diesel off.

Have you loosened the plate on the injector pump to check that the pump pin is engaged properly in the governor rack?

If you haven't done bled the high pressure line already, slightly loosen the fitting at the injector and crank the engine for a bit to bubble diesel out (use a rag), and then promptly tighten the fitting. A little bubble in the high pressure line can cause over-fueling as well. I think that the Yanmar engines are very solid reliable engines generally, but unlike some other diesels, they do have trouble clearing air in the high pressure line.

I think that the odds on bet is still a bad injector, if you have already bled the high pressure line.

All the best,

2Pbfeet

I will double check the inlet to the injector pump. I have not bled the high pressure line to the injector. I will do both of those. The governor is hooked up to the injection pump properly I did check that.

Thanks!!


Sent from my iPhone using Tapatalk

 

[Captainscall]

I pulled the exhaust cover off and looked as far as I could into the muffler. I do not see any signs of a spark arrestor. My new injector should be here in a few days. I managed to break the tip off the injector at some point during my tests. I’m hoping it was just a leaking injector. Will update when new one gets here. Thanks!!

Sent from my iPhone using Tapatalk

 

[CallMeColt]

Does the injection pump look like it was ever messed with, removed, or adjusted in anyway?

 

[DieselAddict]

I can tell ya from first hand experience if there is any air getting into the high pressure pump, even a little, it will spit and sputter and overall be a very unhappy little camper. I just went through that problem with the HDT that I'm working on. It sounded like the timing was WAY off and I think it was BUT it was caused by the fuel being injected very late due to the squishy air in the line.