Opinions on MEP-831A

DieselAddict said:

The connections look right. I see no problems there. The first generator I did this battery setup is still going strong after more than 2 years. I hope you just got a bad battery. And I hope Yusa steps up and replaces it for you.

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Battery was bad and neither Yusa nor the original seller would stand behind it.

Yesterday my 831a was running fine at 110% even though it was blowing more white smoke than I would like. I drained oil and the fuel that was in it. Today I put in Rotella 15W40 and fresh diesel. Now I can't get it to run past 2.5 kw. It bogs down and blows black smoke. The only thing I haven't changed is the fuel filter. It had 5W30 in it when it was running properly. I assume it had JP8 but I don't know for sure.

Help!

I believe you have air in your fuel system . I had similar issues on my MEP531A s Had to run the 1 almost 2 hrs till it cleared up . You can also try bleeding the system.

R Racing said:

I believe you have air in your fuel system . I had similar issues on my MEP531A s Had to run the 1 almost 2 hrs till it cleared up . You can also try bleeding the system.

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That would make sense since I ran the fuel pump some after I drained the fuel. What is the best way to bleed the fuel system. I'm not too sure my neighbors are happy with me running it for hours blowing smoke.

Id try turning on the fuel pump and take your fittings loose close as you can to the injector . And let it run til you see no air or bubbles coming threw the line.

Mine came without fuel and it bled out pretty quickly. Probably the easiest one that I've ever done. That said, with the engine running it wouldn't hurt to crack the injector nut and see if you get any air out. After that, I'd start looking at the fuel filter. Maybe there was some sludge in the tank and you stirred it up. Is the fuel in the bowl crystal clear?

After you are sure you've purged the fuel system I would recommend looking at the air intake path. Black smoke is a sign of too much fuel in relation to the amount of air. An air restriction will put you down on power and make it blow black smoke. Lots of black smoke.

Take a look at the intake and make sure the intake hose hasn't collapsed on the inside or nothing else is obstructing things. Make sure your little buddy can breathe.

Tell you a little story... I bought a pump from our favorite surplus site; it was a cherry deal because the unit was brand speaking new. Even had the factory "unit shipped without oil" tag on it. Unfortunately, although it would start good and idle well, once you revved it up the engine would chug and blow black smoke. I couldn't figure out what was wrong so I gave it to a friend who was a diesel mechanic. After tinkering with it for a while he got the engine to run great. Thinking he had the problem solved, he put everything back together and it ran like crap again. WTF??? Digging into it further, he found a red storage plug had gotten sucked up inside the intake tube so the engine couldn't breathe. When he was testing the engine he had the air cleaner cover off so there was no restriction. He quckly knocked the plug out and the problem was solved.

DieselAddict said:

After you are sure you've purged the fuel system I would recommend looking at the air intake path. Black smoke is a sign of too much fuel in relation to the amount of air. An air restriction will put you down on power and make it blow black smoke. Lots of black smoke.

Take a look at the intake and make sure the intake hose hasn't collapsed on the inside or nothing else is obstructing things. Make sure your little buddy can breathe.

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OK I have cracked the injector nuts while running. Both on top of the engine and on the front side where the hard fuel line goes into the engine. Diesel came squirting out so I'm pretty sure I don't have air in the lines.

I changed the oil and made sure I had exactly 38.4 ounces. Also cleaned the oil filter.

I'm having the same problem. It bogs out with heavy black smoke at 2.7kw

Just two days ago I was running it no problem at well over 3kw.

I removed the air filter and it does the same thing. The air intake tube is clear.

Could using 15w40 oil cause this? Diesel vs. JP8?

Im going to go get a new fuel filter and see if that does the trick.

Thats a good question. I've been using the Rotella 5w40 in my air cooled engines including the 831 and they pull full load with no problem.

Diesel over JP8 should not be the source of the problem.

Let us know what you find out.

DieselAddict said:

Thats a good question. I've been using the Rotella 5w40 in my air cooled engines including the 831 and they pull full load with no problem.

Diesel over JP8 should not be the source of the problem.

Let us know what you find out.

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OK. Going to get a fuel filter and if that doesn't work I'll switch to 10W30 that Yanmar recommends for this engine.

Chris I'm a big fan of the Rotella T synthetic and if I end up keeping this genset that's what I will use.

Neither the fuel nor the oil would be the cause of your problems.

I installed a new fuel filter and changed oil to 10w30 and same problem. At 2.7kw it bogs down, blows black smoke and eventually trips the breaker.

The only other piece of information I can add is that after I filled it with oil yesterday I couldn't get it to turn over. It would try to crank but wouldn't. I had to move the decompression lever down to get it to start. I guess it's possible I overfilled it with oil but when I drained it today the correct amount came out.

I'm going to start reading the TM but would love to hear any other suggestions.

What type of damage happens to these Yanmar's if overfilled with oil?

One other thing I did put some degreaser on the engine yesterday and washed it off with a light spray of water. I was careful not to get the electronics wet. Wondering if I messed something up.

Thanks for all the help. I'm hopeful I can revive this genset without major repairs.

You know my second unit did a simular thing. Ended up with a broken piston ring. After that it was hard starting and wouldn't go full load . Perhaps some how you hydrolocked the engine ??

R Racing said:

You know my second unit did a simular thing. Ended up with a broken piston ring. After that it was hard starting and wouldn't go full load . Perhaps some how you hydrolocked the engine ??

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I'm guessing it has to be related to not being able to crank it. How hard is it to replace a broken piston ring? I have no experience overhauling engines but I'm a quick learn.

hammick said:

What type of damage happens to these Yanmar's if overfilled with oil?

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Unless you have the unit flipped on it's back when trying to fill it with oil, it's impossible to over fill it. Honda's control their oil level a simular way: you simply fill it until the oil comes out of the hole. You can try to put more in, but it'll just run back out.

How do you know that it's putting out 2.7 kW? How many legs is the load spread over? Why were you trying to overload it the other day?

hammick said:

I'm guessing it has to be related to not being able to crank it. How hard is it to replace a broken piston ring? I have no experience overhauling engines but I'm a quick learn.

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Tearing the engine down isn't hard but to get the piston out you'll need to pull the rod cap and I'm pretty sure this will require the engine to come out. Hopefully you don't have to pull the crank because pulling and installing the stator is a bitch. The good news is that Yanmar parts are incredibly cheap. In another thread I have the parts manuals posted. With the parts numbers in hand you can order them directly from a Yanmar dealer.

If I remember correctly you don't need to pull the engine. I believe you can just slide the jug up and off, and install the new rings. Then carefully slide the jug back on with a ring compressor to get them installed. Pretty easy if I remember right.

I installed a new fuel filter and changed oil to 10w30 and same problem. At 2.7kw it bogs down, blows black smoke and eventually trips the breaker.

The only other piece of information I can add is that after I filled it with oil yesterday I couldn't get it to turn over. It would try to crank but wouldn't. I had to move the decompression lever down to get it to start. I guess it's possible I overfilled it with oil but when I drained it today the correct amount came out.

I'm going to start reading the TM but would love to hear any other suggestions.

What type of damage happens to these Yanmar's if overfilled with oil?

One other thing I did put some degreaser on the engine and washed it off with a light spray of water. I was careful not to get the electronics wet. Wondering if I messed something up.

Thanks.

He'd be too lucky if it has a removable cylinder. Thankfully I only had to do a head gasket on mine. The worst part of the job was removing the muffler mounting bolt.