Kubota kx71 engine trouble bogs/fuel starved

[mje171]

I have a kx 71 excavator with 2200 hrs with the V1505 engine. This machine will run great for about 45 minutes. Lots of power, no smoke then instantly it will bog and act fuel starved. Engine will vibrate and activating any hydraulics will almost or sometimes stall the motor. Increasing throttle will not gain RPM. There is a faint white/grey smoke while this is happening but very light. Shutting the machine off and letting it cool for a few minutes and it will be fine again until it gets hot.

no bubbles in the coolant or smell of anti freeze.
I have cleaned replaced fuel lines and filters. I have bypassed the entire fuel system by feeding the injection pump direct from a tank on the roof. Still does it. I have replaced the injector pump and had the injectors tested.
compression is 400psi hot across all four cylinders two are 375 cold. new is 539-569 rebuild spec is 327
I have replaced the stop solenoid and ran with out it. same outcome.
Oil pressure is 60-80 cold and 40-60 hot

It does not act as if the engine is loaded e.g. hydraulic function is stuck it acts as if it is starved for fuel. This machine starts right up in any weather. and will start immediately after this occurs so it's not a seized bearing/piston

Help please... Any ideas?

 

[Jgm]

If injectors are Good, it could be, low cylinder compression,leaking or broken valves, piston ring wear or broken, did you do a compression test?

 

[mje171]

Yep, in my first post. compression is(375, 400, 375, 400 cold)(375,400,400,400 hot) from fly wheel to fan. It's a bit low but does not explain why it runs like a champ even at operating temp, but after a period of time it will just immediately fall on its face. If it is a valve or piston ring problem it should be hard starting or do it all the time in my opinion.

 

[Jgm]

Check on your fuel pump the inline, you should be able to scores the fitting out, underneath should be a spring and in the hole if you take a small pick and pull out the brass fitting, which is possibly contaminated or plugged up

 

[mje171]

Thank you for the replies. Please note I bypassed the entire fuel train by feeding the injection pump direct from a tank on the roof. All return lines are also clear. The injection pump has been replaced and the injectors have been tested good.

 

[Farmer Brown]

This sounds like the same issue I'm having. Did you ever find the root cause of the problem?

 

[4bz]

When you connected the rooftop tank to feed the injection pump, was the tank line for the test different from the regular feed line to the pump? The description of the engine working fine until it gets hot could be a mechanical or electrical fault. A possible mechanical fault could be a hairline crack in the fuel line that feeds the injection pump: when it gets hot it opens, air is pulled into the pump, and the engine starves for fuel (I suggest this in case your rooftop tank test setup was connected in part to an existing injector pump feed line). I can also think of two electrical faults that could cause the symptoms that you describe. 1. A faulty coolant overflow sensor (the sensor that prevents the engine from running when the coolant level is low), and 2. A crack in the engine control module circuit board that opens with heat and vibration (if your engine has an electronic control module).

 

[Bodog]

I have a kx 71 excavator with 2200 hrs with the V1505 engine. This machine will run great for about 45 minutes. Lots of power, no smoke then instantly it will bog and act fuel starved. Engine will vibrate and activating any hydraulics will almost or sometimes stall the motor. Increasing throttle will not gain RPM. There is a faint white/grey smoke while this is happening but very light. Shutting the machine off and letting it cool for a few minutes and it will be fine again until it gets hot.

no bubbles in the coolant or smell of anti freeze.
I have cleaned replaced fuel lines and filters. I have bypassed the entire fuel system by feeding the injection pump direct from a tank on the roof. Still does it. I have replaced the injector pump and had the injectors tested.
compression is 400psi hot across all four cylinders two are 375 cold. new is 539-569 rebuild spec is 327
I have replaced the stop solenoid and ran with out it. same outcome.
Oil pressure is 60-80 cold and 40-60 hot

It does not act as if the engine is loaded e.g. hydraulic function is stuck it acts as if it is starved for fuel. This machine starts right up in any weather. and will start immediately after this occurs so it's not a seized bearing/piston

Help please... Any ideas?

Did you ever find the problem as i am having the same now on my kx71