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Tractor Forum > Lawn Garden Tractors > Kubota > Kubota Loss of power? - Tried Everything (need new ideas)

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Old 05-09-2010, 11:11 PM   #1
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Kubota Loss of power? - Tried Everything (need new ideas)

I have Bobcat excavator 337 with a 4 cylinder Kubota Diesel. The problem has been going on for a year or more when it slowly started loosing power. Here are the items I’ve completed.

1) Put on a new cam run lift pump mounted to engine
2) Added an electric lift pump in place of the primer ball (pull through pump so I can leave it off if I want) just to see if the cam itself was worn out operating the cam lift pump (process of elimination).
3) Took injection pump off, with all injectors, had them rebuilt.
4) Installed new rings (over 400psi in all cylinders now +/- 20psi)
5) At this point brought is the the Bobcat dealer who said “you need a new pump”. OK….$5600 later I get it back. Still looses power.
6) YES…..replaced all the filters

Took it back to the dealer who ran every hydraulic test on it that they could, took the pump back apart again, (found a faulty pump controller), put it all back together and they (and I am too) are confident the pump side of the system is right.

So right now this is how it acts. I can start it up and runs great. I have about 4 to 8 minutes of full power at which time it starts to bog down, slowly at first, then the engine starts a light knock (more like a tap…growing to a knock), if I stop digging/driving the RPM immediately goes right back up. Then if I touch one of the hydraulics is pulls back down just as fast. (in this state if I were to push the drive levers full forward it would kill the engine in about 2 ft of travel). I can limp around at this state (very very slow crawl, basically the engine cannot take any torque). The machine does have a temp gage which does show movement but not hot, the oil pressure alarm is not functional, and when its running I can grab the hydraulic return line before it goes into the hydraulic radiator with my bare hand so it is not that hot. I took the thermostat out the other day (just in case it was stuck shut…no difference). At this point I’m thinking it might be overheating (It would not surprise me if the gage is not functioning) but the radiator does not overflow when running (YES..its full), or maybe the oil pump is out (but if it was I think I would have had something real bad happen a long time ago)…… These are my current guesses…but I’ve been guessing for close to a year and $8000!!.... I’m hoping someone has a few thoughts that I might be overlooking. HELP PLEASE!!

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Old 05-10-2010, 10:48 AM   #2
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Could it be that the thermostat was stuck open, and so it's not allowing the coolant to fully warm up, which would affect your timing? In other words, have you dropped in a new therostat to see if this would make a difference? Not likely, but it's a shot! I assume you have checked all the filters.
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Old 08-25-2010, 10:48 PM   #3
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I would check the fuel return line from your injection pump to the fuel tank. You should have a return flow of fuel returning to the tank. If you have no fuel or air bubbles while the engine is running are an indication of fuel problems. Some injection pumps use a low pressure to advance the injection timeing, a blocked check valve or pinched return line offsets injection timeing leading to power loss and in some situations failure to start and run. Fuel supply from tank to pump must be sufficient .
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