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Old 02-03-2019, 01:16 PM
Fitch Fitch is offline
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Default Engine runaway with clouds of black smoke.

Hi,

Not been here for a while. But, I have a problem that's got me puzzled.

My RTV (2004) started fine (temperature about -2F) and was left to warm up while I did some quick tasks in the barn. It started to make an odd noise and when I looked down the barn aisle, there was so much black smoke I thought something was on fire.

What I discovered was the engine running at what sounded like maximum rpm making an incredible cloud of black smoke. I turned the key off but it had no effect. Tried turning the key off several times. In desperation I raised the bed and tried the throttle connection on the fuel pump but moving that had no effect on the engine's operation. As a last ditch effort to get it shut down before something worse happened, I used the pliers on my leatherman to squeeze the rubber fuel line which shut it down after a few seconds.

At this point I've no idea what caused this behavior. Have any of you seen it?

Thanks
Fitch
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Old 02-03-2019, 04:41 PM
aurthuritis aurthuritis is offline
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could have been pulling oil past the pcv or running on fumes in the barn. governor could have problems. take the air cleaner assy off and look for fresh oil in the intake manifold. get a board to cover the intake with in case it runs away again and start it to see if it repeats.
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Old 02-03-2019, 11:05 PM
Colorado_High Colorado_High is offline
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It sounds as if the cable running from the foot pedal might no longer be controlling the injector rack. It is a completely mechanical pump-line-nozzle fuel system as far as I know. I think the foot pedal cable goes to both the transmission and the injector rack.
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Old 02-04-2019, 04:17 AM
Fitch Fitch is offline
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Thanks for the suggestions. I'll follow up on them.

Fitch
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Old 02-04-2019, 11:14 AM
Colorado_High Colorado_High is offline
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On second thought, even if the injector rack was fully open, it should not be very heavily smoking. On the other hand, if it was a restriction of airflow, the engine should still cut off with the ignition key. On a mechanical diesel engine, turning off the key has to stop the fuel flow, since there are no spark plugs to turn off. Not sure how the Kubota shuts off the fuel flow.
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Old 02-04-2019, 12:38 PM
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Quote:
Originally Posted by Colorado_High View Post
On second thought, even if the injector rack was fully open, it should not be very heavily smoking. On the other hand, if it was a restriction of airflow, the engine should still cut off with the ignition key. On a mechanical diesel engine, turning off the key has to stop the fuel flow, since there are no spark plugs to turn off. Not sure how the Kubota shuts off the fuel flow.
there is a solenoid that opens and closes the rack restricting the flow of fuel.
i suspect from the description that there is a governor or rack problem because it the engine was self fueling from fumes or bypassed engine oil the op wouldn't have been able to shut it down by pinching the hose. usually in these cases only restricting the air will save the day.
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Old 02-04-2019, 05:31 PM
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Fuel return problem. Excess fuel dumping at nozzles due to poppets' being held open because of back pressure. Injection timing goes to shit, thus all the smoke.
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Old 02-05-2019, 05:10 AM
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Quote:
Originally Posted by foxalaska View Post
Fuel return problem. Excess fuel dumping at nozzles due to poppets' being held open because of back pressure. Injection timing goes to shit, thus all the smoke.
Thanks. That sounds like a really good hypothesis.

Nothing that I can see or inspect is abnormal. But it was -2F and it didn't have winterized fuel init so the poppets could be dysfunctional due to precipitated wax/gel.

Fitch
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Old 02-07-2019, 04:24 PM
Alaskanassasin Alaskanassasin is offline
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Sounds like oil getting in combustion chamber, maybe a broken ring on a piston causing blowby... but if cutting off the fuel killed it I dunno. How many hours on it?
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Old 02-07-2019, 04:30 PM
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Oil smoke is blue and has a distinctive odor. Over fueling creates a black smoke.
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Old 02-08-2019, 05:04 AM
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forums would be much more helpful if we were updated on the outcome of such things.
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Old 02-08-2019, 01:10 PM
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I agree with foxalaska that it is likely a fuel delivery issue. Sometimes a single injector will stick open and cause black smoke and a knock but not a runaway problem. Runaway definitely points to a more "universal issue". Typically I would say that it's pulling oil from somewhere but the fact that killing the fuel supply ended the runaway kinda squashes that theory (you should double check that though since this is one of the most common runaway causes). However, I am surprised that pinching the fuel line shut the engine down and yet turning the key off had no effect. This certainly hints at a fuel problem, but turning off the key should close the fuel solenoid and, in theory, have the same effect as pinching the fuel line, so if it was simply a backpressure issue I would think that turning off the key would have shut the engine down. Had the engine been sitting for a while (weeks or months) before this problem occurred? Have you successfully run the engine since the problem? Have you checked the function of your solenoid? I know that in other mechanical diesel engines this is one of the most common fuel delivery related failures. What do you think foxalaska? I have never seen it before, but do you think that at WOT a fuel cutoff solenoid could be forced to stay open even with the key off?

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Old 02-09-2019, 10:05 PM
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i forgot to mention that an overfull cranckcase will cause these symptoms to. check the diaphragm fuel pump on the side of the block for leakage.
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Old 02-13-2019, 12:03 PM
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When this happens on any diesel, most of the time it is a injector
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Old 02-15-2019, 05:26 PM
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I have the diagnosis. The mechanic at the Kubota dealer had a suspicion and had the problem diagnosed in about twenty minutes.

There is a plate on the side of the injection pump that is retained by 4 tiny flat head machine screws. This plate holds a sliding rack.

Two of the screws were missing, the other two were so loose the sliding rack ceased to function. The screws are probably someplace in the 2,908 hours of sludge in the bottom of the oil pan. They had a clear path to get there through a hole much much bigger than they are. The screws are really tiny.

I attached a picture of the injection pump to show the cause.

I've no idea when the first screw, or the second, dropped off the pump. The bottom two were loose when the thing started to malfunction. Presumably the top ones came out a while ago. The engine ran just fine right up until it had a problem.

The four holes showed evidence of the screws vibrating. Kubota doesn't sell the screws as a separate part, other than this the RTV is in great condition, so I chose to get a new injection pump rather than cobble it together with some after market screws and hope they stayed in place.

The next time I change the oil, I'll see if I can find a snake with a cylindrical magnet on it that I can slide into the oil pan in an attempt to capture the screws and pull them out. The aluminum oil pan gives me a shot at it anyway.

Thanks for all the suggestions folks. Much appreciated.

Fitch
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Old 02-15-2019, 05:34 PM
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Quote:
Originally Posted by aurthuritis View Post
forums would be much more helpful if we were updated on the outcome of such things.
I agree 100%. See diagnosis post with a picture. I had the diagnosis Thursday morning, but wasn't able to get a good picture of it while it was in the shop. I had them save the pump for me so I could post a picture of it.

Fitch
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Old 02-15-2019, 07:23 PM
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Thank you Fitch . collie
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