L3800 HST "Runaway"/over rev

[Buzzaro]

Title is a little misleading, I don't think it's a true runaway condition but unsure how else to describe it. I've had this happen twice now. Mowing fairly thick grass with a Gearmore gml69 flail. A little oversized as the machine is working pretty hard. The engine temps are climbing but not into the red (radiator and screen has been checked, cleaned, and blown out). So while mowing under heavy load and full throttle (RPM's at the PTO 540 mark) the engine RPM's suddenly climb and the tach is pegged. Both times I've immediately pushed the throttle level all the way back to idle but the machine keeps cranking and black smoke starts to come out. Each time I've turned the key off and then the engine does shut down. Now all this take place within 2-4 seconds so to be honest, I am unsure if the RPM's begin to drop before or after I've turned the key off. Each time it fires right back up and continues to operate normally. I have checked the mechanical linkage from the throttle lever to the injection pump and it moves freely by hand through it's full range and returns normally by the spring.
Looking for ideas on what the issue could be.
Thanks

 

[Russell King]

That does sound like a true runaway situation.

It may be sucking oil from the crankcase or somewhere to run on that instead of the fuel.

Look into the air intake system to see if there is an oily film, find out what is connecting the air system to the crankcase and fix whatever may be going on.

I would recommend NOT using it until you find the problem.

 

[loggin]

Title is a little misleading, I don't think it's a true runaway condition but unsure how else to describe it. I've had this happen twice now. Mowing fairly thick grass with a Gearmore gml69 flail. A little oversized as the machine is working pretty hard. The engine temps are climbing but not into the red (radiator and screen has been checked, cleaned, and blown out). So while mowing under heavy load and full throttle (RPM's at the PTO 540 mark) the engine RPM's suddenly climb and the tach is pegged. Both times I've immediately pushed the throttle level all the way back to idle but the machine keeps cranking and black smoke starts to come out. Each time I've turned the key off and then the engine does shut down. Now all this take place within 2-4 seconds so to be honest, I am unsure if the RPM's begin to drop before or after I've turned the key off. Each time it fires right back up and continues to operate normally. I have checked the mechanical linkage from the throttle lever to the injection pump and it moves freely by hand through it's full range and returns normally by the spring.
Looking for ideas on what the issue could be.
Thanks

It looks like your model has the interim tier 4 motor which I believe has the vent on the valve cover with a tube that goes to the intake. This vent releases crank case positive pressure. I hypothesize that under full throttle and high load you might be getting greater blow-by at the piston rings. This might be enough to force some oil into the vent tube and then be sucked into the intake thus causing a temporary run-away condition.

Just a thought..

 

[Buzzaro]

It looks like your model has the interim tier 4 motor which I believe has the vent on the valve cover with a tube that goes to the intake. This vent releases crank case positive pressure. I hypothesize that under full throttle and high load you might be getting greater blow-by at the piston rings. This might be enough to force some oil into the vent tube and then be sucked into the intake thus causing a temporary run-away condition.

Just a thought..

Thanks. I just checked that this morning and there didn’t seem to be any oil in the intake. How much oil would I expect to feel or see to be an issue? I wiped inside with a white rag and while it was ever so slightly oily, there was no black residue on the rag. More oily in the way that sometimes happens when you grab the diesel handle at the pump, maybe even less so.

 

[loggin]

Thanks. I just checked that this morning and there didn’t seem to be any oil in the intake. How much oil would I expect to feel or see to be an issue? I wiped inside with a white rag and while it was ever so slightly oily, there was no black residue on the rag. More oily in the way that sometimes happens when you grab the diesel handle at the pump, maybe even less so.

Have you checked the oil level for any change? Burning oil would reduce level. Fuel or hydraulic fluid getting into the crank case would increase level. If the oil level is high this would increase the likelihood of it being sucked into the intake.

It is hard for me to know how much you would see at the intake. I would suspect you would see some sign of oil. Perhaps someone that knows more about that can chime in..

 

[Buzzaro]

Have you checked the oil level for any change? Burning oil would reduce level. Fuel or hydraulic fluid getting into the crank case would increase level. If the oil level is high this would increase the likelihood of it being sucked into the intake.

It is hard for me to know how much you would see at the intake. I would suspect you would see some sign of oil. Perhaps someone that knows more about that can chime in..

I had just changed the oil so I checked the dipstick and it was way way over full. Seemed like pretty clean oil, no diesel smell, not milky or thin. A google search had someone else with the same overfill issue. I had added the 7.5 quarts the manual said, but maybe I didn’t get it all out or something. Plus I didn’t check did check the dipstick when I filled it up. One more lesson to learn the hard way. In any case,I removed some oil down the correct level and then I risked it and ran the machine again with the flail. Ran normally, and the temp wasn’t climbing as the day before. Hopefully that was the issue and it’s not a lesson I learn the REALLY hard way.

 

[Russell King]

Keep an eye on the oil level for a couple of weeks until you are sure it is stable. There may be some seal failure on the hydraulic pump that lets hydraulic fluid get into the engine case. That may not be possible on your tractor but was on mine.

 

[mdhughes]

I had just changed the oil so I checked the dipstick and it was way way over full. Seemed like pretty clean oil, no diesel smell, not milky or thin. A google search had someone else with the same overfill issue. I had added the 7.5 quarts the manual said, but maybe I didn’t get it all out or something. Plus I didn’t check did check the dipstick when I filled it up. One more lesson to learn the hard way. In any case,I removed some oil down the correct level and then I risked it and ran the machine again with the flail. Ran normally, and the temp wasn’t climbing as the day before. Hopefully that was the issue and it’s not a lesson I learn the REALLY hard way.

There are two drain plugs in the oil pan, if you didn't drain both sides you would have over filled it.

 

[TECH101]

Sounds to me like a bad injection pump or possibly worn out cylinders / pistons

Either way I would start with a compression test first