Dewey MEP 531a running horrible

[markgjsquires]

Recently purchased two 531’s. One had fuel lines removed. Replaced the lines. Fresh fuel and oil. Few cranks and runs great. second one did the same maintenance schedule to. Does not run so well. Will start and run but when manipulating throttle anything over half throttle it dies out spits sputters and smokes. I’ve checked oil level as many say affect it. It’s right in the middle. Fresh fuel and filter. New lines. but do not get any fuel from the return line. Is that common on these? Even the generator I have that runs good doesn’t show any in return line. Any ideas would be much appreciated. Thanks.

 

[1800 Diesel]

I'm still learning about these engines myself, but can offer a few things to consider.

1. Check the fuel plunger on the injection pump as it may be sticking a little. I've only seen these fully stuck and they have to be freed up. Since your engine is running at lower speeds, this could be a fuel metering issue.

2. If #1 doesn't apply, remove the valve cover to confirm valve lash and also verify both intake & exhaust valve are fully opening & closing.

3. If you haven't already done this, you should loosen the fuel line fitting on the injector and crank the engine over to confirm all air is bled from the line.

4. To confirm proper injector function (volume & spray pattern), you can remove the injector and reconnect to the high pressure fuel line (with the injector outside the engine). Then crank the engine over & observe injector function. (Caution: Don't get sprayed with the fuel mist!)

5. Check air filter and housing for any obstructions.

Edit: Forgot to mention that fuel injection timing is set by the thickness of the shim gasket(s) under the injector. If someone mixed these up, this could cause the plunger stroke to change, which would either advance or retard fuel delivery timing. Another remote possibility--the external throttle linkage is not correctly engaged to the injector metering linkage inside the engine. This can be seen by removing the small triangular inspection plate This plate covers a small "window" or port through which you can see the throttle linkage "bars" that should be engaged with the ball on the injection pump linkage. If the ball is not inside the two bars, this needs to be corrected.

A couple questions:

1. What type/color smoke are you seeing?
2. Any unusual noises when you start to throttle up? Backfiring, knocking??

I'm sure there may be other possibilities but wanted to offer a few that came to mind. Good luck with the troubleshooting!

 

[markgjsquires]

I'm still learning about these engines myself, but can offer a few things to consider.

1. Check the fuel plunger on the injection pump as it may be sticking a little. I've only seen these fully stuck and they have to be freed up. Since your engine is running at lower speeds, this could be a fuel metering issue.

2. If #1 doesn't apply, remove the valve cover to confirm valve lash and also verify both intake & exhaust valve are fully opening & closing.

3. If you haven't already done this, you should loosen the fuel line fitting on the injector and crank the engine over to confirm all air is bled from the line.

4. To confirm proper injector function (volume & spray pattern), you can remove the injector and reconnect to the high pressure fuel line (with the injector outside the engine). Then crank the engine over & observe injector function. (Caution: Don't get sprayed with the fuel mist!)

5. Check air filter and housing for any obstructions.

Edit: Forgot to mention that fuel injection timing is set by the thickness of the shim gasket(s) under the injector. If someone mixed these up, this could cause the plunger stroke to change, which would either advance or retard fuel delivery timing. Another remote possibility--the external throttle linkage is not correctly engaged to the injector metering linkage inside the engine. This can be seen by removing the small triangular inspection plate This plate covers a small "window" or port through which you can see the throttle linkage "bars" that should be engaged with the ball on the injection pump linkage. If the ball is not inside the two bars, this needs to be corrected.

A couple questions:

1. What type/color smoke are you seeing?
2. Any unusual noises when you start to throttle up? Backfiring, knocking??

I'm sure there may be other possibilities but wanted to offer a few that came to mind. Good luck with the troubleshooting!

Thanks for the response. I have cracked the line on the injector to assure all air has been removed from the line. I have also swapped injectors between the two generator sets and the response was same with both injectors. It emits intermittent puffs of black and/or blue smoke with a knocking sound occasionally. Similar to the knocking a Diesel engine gets when it’s fed too much starting fluid. I’m assuming that it’s something with valve adjustment being the set has 134 hours on it it may have never been adjusted? Either that or something with timing. I will dice into your suggestions tonight and see if I can come up with anything. Thanks again.

 

[1800 Diesel]

If you're getting the same running condition with the known-good injector, this points to any of the other items mentioned. Just go through the check list, not necessarily in the order provided, maybe the easiest one first, such as intake obstruction, timing, valves...obviously we're all hoping this isn't something major on any of the engine components. Keep trying--you'll get it sorted out!

 

[markgjsquires]

I haven’t gotten chance to troubleshoot the engine anymore but I do notice the injection pump
Had been removed being the nuts have the paint off of them as well as appears to be a new shim
Installed. Do you by chance know where I could source shims if I find I need them? Thanks

 

[1800 Diesel]

I haven’t gotten chance to troubleshoot the engine anymore but I do notice the injection pump
Had been removed being the nuts have the paint off of them as well as appears to be a new shim
Installed. Do you by chance know where I could source shims if I find I need them? Thanks

Ask for Robert at 888-687-0539. This is a Yanmar dealer in Baton Rouge, LA. He will need your engine's model number.

Yanmar Parts | Diesel Engines | Authorized Dealer

Great selection of Yanmar engine parts online! Diesel Parts Direct is an Authorized Dealer and all parts are covered by a 6-month warranty. Shop now!

www.dieselpartsdirect.com

 

[reo12]

The return line is only for fuel leaking past the injector components. Typically only single drops of fuel over minutes of operation. It could take hours of running to notice fuel in the line. Mine ran as you state yours does. I found the valves were terribly out of adjustment.

 

[Dieselmeister]

Have you tried removing the stainless steel spark arrester on the muffler. If that is plugged it could cause too much backpressure at full throttle. This is the easiest test before you dig into the machine further.

 

[markgjsquires]

I have tried the spark arrestor and removed it that made no Difference. I took off the injection pump and that plunger seems to be free and working correctly. The ball on the throtttle control is in between the two arms so that’s correct. I’ve removed injector and could see a nice mist out of the four holes so that appears correct. I installed a new hose and elbow from filter assembly to injection pump. Bled lines at injector and minute i saw steady fuel I tightened it up it fires right up. Fresh fuel. I am using 10w30 oil since all I had at home to do a test run with. Didn’t thing that would matter much. Only odd thing is the hertz gauge is pegged. I can only get it to calm down if I get the engine to idle down. Volts read <50 whether at idle or I manipulate the governor to get it to rev up for a minute. When I do that it black smokes heavily and notice sparks from the arrestor so I know it’s getting shoved a lot of fuel. Otherwise when I don’t manipulate anything it runs rough not at full throttle with blue smoke. And knocking. I think I’ve narrowed it down to timing far as I can tell unless something with the generator assembly itself is making it run this rough but I doubt it? Thanks for the help and pointers. I’ll keep at it and see what I can find.

 

[glcaines]

Have you confirmed that the valves are moving and not stuck and that the gap is correct? If not, I would recommend removing the valve cover and looking for any problems there. You have already eliminated some potential causes. Don't give up, you'll find the cause.

 

[markgjsquires]

I believe I have. I removed the air cooling cover and moved the flywheel to the correct timing mark to assure both valves were closed and I was able to fit a .006” gauge under them. Not a .010 so assuming that will be close enough? I will be away for a couple days but will try again when I get the time. Thanks

 

[Dieselmeister]

Question: You say - when manipulating throttle anything over half throttle it dies out - Are you manually holding the throttle to start the engine? On the 531's, the throttle lever is either on - latched, or off -tripped.

Some things to think about:

The pegged hertz gage - do you have a way to measure the frequency - Fluke, or Killawatt? Any way to measure the RPM? Unloaded idle is above 60Hz. This is normal (3750 rpm unloaded, 3600 at full load).
The smoking at high power sounds like insufficient air. Is anything restricting the air intake?
Do the valves depress sufficiently when they should be wide open?
The oil level - I had one unit with two different length dipsticks! Someone had cut one short. Blue smoke is usually oil.
Injection timing - late injection will cause incomplete combustion and smoke. The TM covers how to check / adjust the timing.

 

[markgjsquires]

When I say “manipulating the throttle” it’s by holding the lever when pressing the off tab so it can’t shut off completely then by hand, slowing the engine or speeding it up. I will check the oil so much if they are different than my “good” generator. I can see that the injection pump had been removed and a new shim installed being that it’s not painted as my other one is so my guess is on timing. I will work on it more in a few days to see what I come up with. Thanks.

 

[robson1015]

I would remove some oil from the crankcase and see if runs better. It's worth a try... I used a large syringe or turkey baster and sucked oil out of the fill hole.

 

[markgjsquires]

Here’s a video of it running showing how it runs and what I mean by manipulating the throttle. Can also take note of the hertz gauge pegged and the volts not changing either. Perhaps it’s running rough because something with the generator is wrong cause it to be under load.

 

[Dieselmeister]

If it's being bogged down by the generator, it's either mechanical or an electrical overload. I doubt it's mechanical, since you would hear that and most likely see sparks. To rule out a generator internal electrical problems I would disconnect the voltage regulator, and tape off the leads, then run the engine. If it runs good, then there is something wrong in the generator, or wiring. If it doesn't then it's most likely something in the engine. It is easy to check the injection timing to see if that is correct.
Some other thoughts:
With the main output breaker open, does the voltmeter on the panel show any volts?
Are the governor springs on the lever the same as on the genny that works?
Do you have any way to measure rpm, or hertz to see what the hertz gauge is really showing?

 

[markgjsquires]

After finally getting the chance to mess with it this afternoon. I checked the timing and that checked out ok. So last thing I could do was swap fuel injection pumps between the known good running generator and the not so good one and there it was. “Bad” one ran great with the different pump so ordered a replacement and will keep everyone informed on if that truly was the problem. Thanks for all the insight and help. Much as was a pain was great way to get to know about my new generators.

 

[robson1015]

Glad you figured it out.

 

[glcaines]

I know replacement pumps are relatively inexpensive, but I would be tempted to dismantle the old pump and see if I could find what's wrong.

 

[Guyfang]

Before ordering a new one, try cleaning the old one. Will not cost you a dime, and might safe you a few bucks.