David Brown 990 don't run good

UP Oliver · Jun 7, 2016

I have a David Brown 990. It was working fine until late last fall when my wife was brushcutting, I was putting metal on the pole barn and could hear the tractor start to labor out in the field. I have more exhaust than usual, and a lack of power. It sounds like it is missing, but I am no expert on what that sounds like. Also, it misfires when I throttle up.

I have replaced the fuel filters, disconnected the air filter for a quick check there, I have used the dope (as one guy I know calls it), Diesel 911, Diesel mechanic in a bottle and Seafoam. I don't see any leaks anywhere in the fuel lines. It still runs poorly.

I don't know what the next step should be. My manual says to bleed the fuel system for misfires among other things. When I have bled the system in the past, once I get it running there has never been any problems like this so I doubt that is the problem? Wouldn't mind some advice on that.

Any help anyone can provide would be appreciated.

Thanks.

rrlund · Jun 7, 2016

Does it have excessive blow by all of a sudden?

Dick2 · Jun 7, 2016

Make absolutely sure that the cap on the fuel tank is venting.

UP Oliver · Jun 7, 2016

Thanks for the reply rrlund. I don't know how to answer that. I just went out there and put my hand under the blow by tube, and can hardly feel a thing, even at 1600 or more rpm. But the little hole at the bottom of the exhaust manifold has exhaust shooting out of there, and that has not occurred in the past that I can remember. There used to be a tube screwed into that hole but the threads are shot, never fixed it. Also, there is exhaust coming out of the manifold at the bottom of the exhaust pipe. I thought maybe my exhaust was plugged so I ran it without that and it still shoots exhaust out of the little hole. There seems to be way to much exhaust right now compared to when it ran good. I noticed that right away the day my wife was out in the field when it started to labor. I was 25 feet in the air on the pole barn so I had a good spot to see it.

Thanks again for your response. I look forward to any more help you can provide.

showcrop · Jun 7, 2016

Sounds like my diesels do when they are not getting enough fuel. One time it was a plugged line where a return Tees into the supply line, another time it was an extra gasket at the filter blocking the filter inlet slots. You could check for an injection pump inlet screen too.

MARK ROBKE · Jun 7, 2016

By more exhaust than usual-do you mean more smoke? If you hear a miss/engine runs rough,you may have a bad injector/fuel nozzle.You can loosen,one at a time,while the engine is idling,the fuel line on top of each injector(the line from the pump). Fuel will leak around the line.After you loosen one,listen to the engine for a change:it should miss worse. Retighten and then go to the next one until you find one that does NOT change the engine.That should be your bad injector.
Another thing-if this miss created smoke,it is over fueling a cylinder,and can wash the rings,causing major engine damage-so don't operate it this way,just run it long enough to diagnose and fix.Check your oil for fuel too-may need to be changed.Mark

rrlund · Jun 7, 2016

OK,shoots my theory then if there's no blow by. I've had rings break,wear around in the groove until they broke through and scored the piston so bad that there was no compression on one cylinder.

Adirondack case guy · Jun 7, 2016

Sideing here with Mark. More smoke indicates that it is not starving for fuel, but dumping raw fuel in one or more cylinders. As he said bad injectors can wash down cylinder walls and cause major engine damage.
Loren

rrlund · Jun 7, 2016

I had a dripping injector in an Oliver 88 one time that burned a groove right down the side of the piston and sleeve.

UP Oliver · Jun 7, 2016

Thank you very much for the reply. I do not have excess oil as far as I can tell. And it is about time for an oil change anyway. Not sure what you mean by smoke, I guess when this tractor runs well I don't even notice exhaust. I guess what I am seeing is excess smoke.

I gave the injector test a shot just now. By loosening the fuel line, two injectors caused a major change in the idle, and basically two did not. With the two that did not, one may have been a slight change in the idle. But nothing like the two that did change the idle. For the two that changed the idle, there was almost no fuel leaking and the idle changed a lot. Just a small turn away from snug caused a major change in idle. For the two that I loosened that did not change the idle, there was fuel squirting pretty well.

How can two injectors go bad all of a sudden?

Thanks again for your help, and also everyone else that responded so far.

caterpillar guy · Jun 7, 2016

What pump do they have? Could the flex ring be bad? Not even sure if they have one. If the return is plugged it can cause problems. Otherwise I vote for the injector or timing jumped.

UP Oliver · Jun 7, 2016

Thanks for the reply, I had the fuel cap off at one time while it was running and it ran like crap then to, so I know that is not the problem.

UP Oliver · Jun 7, 2016

It has a cav pump, although it says DELPHI on the tag on the pump. I don't get why two injectors go bad, I will have to try to clear out that return tube tomorrow. What are the chances that two go bad at once? Any input is great, I have no idea on this topic anyway.

Thanks.

David Brown 990 don't run good

UP Oliver

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rrlund

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Dick2

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UP Oliver

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showcrop

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MARK ROBKE

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rrlund

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Adirondack case guy

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rrlund

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UP Oliver

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caterpillar guy

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