Diesel engine problem

[kudzu04]

I have a Yanmar 20hp 3 cylinder diesel with 1250 or so hours. It has started to run very rough - stumbling, not wanting to rev, surging. It did this last fall and I changed the fuel filter and bled the fuel system and checked for water. It ran well afterwards so I thought my problem was resolved. Last weekend I cranked her up (busted right off) and used it 2 hours with no trouble when the problem came back. It will crank up but shudders very bad and will not rev up. Last fall it would crank up and run varying lengths of time before acting up. I need to be pointed in the right direction. Thanks a lot for any ideas.

 

[davesl708]

Others may know better but I would start with the fuel injectors.

 

[GManBart]

It sure sounds like a fuel problem. Since it's happened more than once, I'd drain the tank, and make sure it's clean. Then I'd disconnect all the lines to the fuel pump, fuel filter, injector pump, and injectors, then use compressed air to make sure they're clear. After that, I'd replace the fuel filter, fill the tank, bleed the lines, and see what happens.

 

[RPW]

After that you'll be looking at injectors and then injector pump.

 

[Billrog]

What's been said and check the fuel pick-up is clear.

 

[kudzu04]

Thanks for the ideas. I'll start at the "gas" cap and clean my way to the cylinders.
Are injectors/pump something I can do at home? I'm handy enough to change parts, just never worked on a diesel.

 

[davesl708]

All of these steps can be done at home if you are inclined. Parts or Shop manual is very handy.

 

[GManBart]

Thanks for the ideas. I'll start at the "gas" cap and clean my way to the cylinders.
Are injectors/pump something I can do at home? I'm handy enough to change parts, just never worked on a diesel.

Generally speaking, injectors and injector pumps are not serviceable by people without the right training, equipment and tools. I've overhauled many engines and restored cars, but I wouldn't mess with injectors/injector pumps except in a dire emergency.

The good thing is that those are the two least likely problem ares. Injectors can often be replaced for around the cost of cleaning and adjusting them. The set (3) I bought for the Perkins in my dozer ran only $150.

 

[NorEaster]

Before you start throwing parts at it-

Drain and clean tank
Blow out supply and return fuel lines
Replace fuel filter
If it has a block mounted lift pump clean the pre-screen out.

Past that you can have the injectors pop tested to see if any are outside of spec, a diesel fuel shop can do it, I believe JD dealers can as well.

 

[holzboat]

How old is the tractor? Sometimes the fuel hoses can start to break down and cause problems that are not visible.

 

[Walkin Horse]

Last year I had a problem with my hoe running bad until it finally quit. I had the diesel germ. I drained the tank and used a suck bucket to clean it. I found an old cap gasket and a leaf in it. The germ was like a snotty mass that was sliding around on the bottom. Once I got it cleaned I have used PS bio cleaner in it.

 

[Billrog]

I doubt very much you'll have to deal with injectors or pump but it may not hurt while your at it to just replace the fuel line as well if you can't see or find nothing obvious. Because like holzboat said some times they break down inside and this could cause intermittent problems as well if the rubber is acting like a flap. Just thought of another thing I've had happen if the fuel line looks wet at all they sometimes get little pin holes and suck air.

 

[oldpilgrim]

did you put fuel conditioner in the tank? You should, especially in winter.

 

[dieseleric]

Could even be a old fuel line collapsing internally. replace old fuel line maybe? I've even seen valve lash do such things getting to tight. That is usually a sign of running rough all the time though.

 

[kudzu04]

How old is the tractor? Sometimes the fuel hoses can start to break down and cause problems that are not visible.

You know, this garden tractor (JD 430) is 24 years old. Original fuel hoses. It does act like it is sucking up air and fuel as it will occasionally rev then hit and miss. I believe I'll try that - either way it needs to be done.

 

[geneP]

I don't think that checking the fuel cap to be vented has been mentioned. A plugged cap vent will cause a vacuum in the tank after running a while. It is a long shot, but can be checked by loosening and see if problem clears up.

 

[markmechanic]

Check air filter for replacement, post Yanmar model & series numbers, thanks.
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