L4600 Diesel Run Away

[BStone]

Craziest thing happened today.

Tractor had not been running good. Cranked and would run, but had no power.
Throttle was operating but did not have much effect on RPMs. Stopped tractor for
30 minutes. Cranked the tractor and for some reason the RPMs were back and throttle was now affecting the RPM like normal. I ran the RPM up to around 2500 and then it happened! The engine ran away! RPM pegged tachometer. Not sure how high they went, I'm guessing 7 to 8,000. I dropped the throttle but with no effect. Turned off ignition, still no effect. Black and and white smoke coming from exhaust. Jumped off tractor and closed valve above the fuel filter. Engine continued to run at excessive high RPM. Finally engine ran out fuel and died.
Black oily soot coated front end loader bucket from the exhaust.
After collecting myself, I turned key with fuel still valved out. No weird noises, seemed to turn over normally. I then valved in fuel and started tractor. Guess what? Tractor started immediately, seems to run fine. Throttle seems to work fine. RPMs responding to throttle and power seems to be back. No smoke either!

Really weird. Does anyone have any clue to what happened. What are chances that my engine is damaged? What would have caused and what to do about it?

My wife witnessed the whole thing and has sworn to me that she will never drive tractor again. Really scary.

 

[BigG]

Go to youtube and type in "run away diesel' you will see what happened.

 

[BAP]

I would not be starting the tractor again until it is fixed unless you want to totally grenade the engine. An uncontrollable diesel will run until it self destructs from too much speed. If it does it once, it will likely do it again.

 

[lugbolt]

Check the oil level.

It's possible that it's way overfull which would cause it.

All modern diesels have the crankcase vent run to the intake manifold. The downside to doing it that way is that if the oil level is excessively high/over full, the engine (diesels anyway) will ingest the excessive oil from the crankcase into the intake and they'll run on their own lube oil. That may explain why there is so much oily soot.

Another government mandate (closed crankcase ventilation). Common rail engines have an oil separator to help with this issue; most mechanical injected diesels don't.

 

[Dave_eng]

The following comments are generic and may not apply to your Kubota.

Kubota has recalled a number of models because of freeze up occurring in the exhaust gas recirculation system (EGR).

The fix usually involved adding electric heaters to keep critical components above freezing. Larger alternators were needed.

When the EGR system did not properly vent the engine, crankcase pressure would build up and then crankcase oil would be forced up the turbo drain line and become fuel for the engine.

When that happened the engine would start running on crankcase oil and the operator had no control over that fuel supply. A runaway would occur.

While freezing is unlikely at this time of year, problems with the crankcase vent system can happen any time.

Inhaling fuel vapors from other sources can also lead to runaways. 18 wheelers delivering gasoline have had this issue when gasoline fumes get sucked into the engine. I had propane delivered recently and noticed the truck had an emergency shut down on the dash. This shut off is a valve on the air intake to choke off the engine's air supply.

To runaway an engine needs a source of fuel and air.

I too think you should be very cautious about starting the tractor until you know why this happened. Involving a dealer would be wise.

Having a mental plan to stop the engine during any future event would be prudent. A CO2 fire extinguisher directed into the engine's air intake is one of many options.

Dave

 

[BStone]

That is the question, what to fix. Not sure what is broken.

 

[BStone]

Thanks. How do I check the EGR? Would that explain the loss of power I was seeing prior to the runaway?
Is it possible the EGR cleared itself during the runaway, and now is okay, meaning I will never be able to know whether it was the cause or not?

 

[BStone]

I should know, but I don't. Does the L4600 have a turbo or not. How do I tell?

 

[rbargeron]

You can look at the L4600 parts drawings here. Doesn't look like it has a turbo - or an EGR. Both would be part of the intake/exhaust system.

To run away your engine got burnable fuel somewhere. Badly worn engines can allow crankcase oil to get sucked up past in the rings - they run until they fail - or air is shutoff somehow.

This short-term runaway sounds more like a slug of something extra-flammable got into the injectors. Check your fuel cans - any chance a small amount of a foreign substance got in? (cleaning solvent, gasoline, etc?)

I can imagine it refusing to start, running rough/slow/smokey, running fast, or stalling. Eventually it may just run normally as it passes.

If the engine seems to run ok now it may have survived it. I'd do compression and cylinder leak-down tests on it before running under load - you'll know more and have more confidence in it.

Good luck - and post back how it goes.

 

[North Idaho Wolfman]

Have you checked the oil level?

If it's high check the hydraulic level, bet it's low, your problem would be the hydraulic pump seal is leaking and dumping hydraulic fluid into the engine.

Now if the oil level is not low, then there is something seriously going wrong with the injection pump or governor.

I would remove the injection pump making sure to remove any shims under the pump and save them, then send pump to be tested.