B1550hst-d loses power

[AMM]

I have a Kubota B1550 hst-D tractor with 756 hours on it. I just serviced/changed...
the eng oil and filter, fuel and air filters
the Hydro oil spin on filter and two screen filters
the three front gear oil locations
I cleaned the fuel tank and replaced the 5/16 fuel lines
I bled the injectors
It runs great until it is under load then it loses power quickly.
I adjusted the 3 point hitch lift arm so it did not over travel and circulate hydro fluid.
I noticed if I raise the bucket while losing power going up hill the power comes back until I stop raising the bucket.
The Fuel gage is pinned at empty even when full. I say this be cause this tractor goes into reduced power mode when the tank is near empty.
any suggestions? Thank you!

 

[Vacula]

I've not owned Kubotas long but have had garden tractors both hydro and gear, diesel & gas all my life so I'll through my 2 cents at it. But..... Is the engine losing power or is this hydraulic power lose? In other words, do you hear the engine struggle with RPM and torque or does the engine stay steady and the hydro is bogging?

 

[JerryMT]

I have a Kubota B1550 hst-D tractor with 756 hours on it. I just serviced/changed...
the eng oil and filter, fuel and air filters
the Hydro oil spin on filter and two screen filters
the three front gear oil locations
I cleaned the fuel tank and replaced the 5/16 fuel lines
I bled the injectors
It runs great until it is under load then it loses power quickly.
I adjusted the 3 point hitch lift arm so it did not over travel and circulate hydro fluid.
I noticed if I raise the bucket while losing power going up hill the power comes back until I stop raising the bucket.
The Fuel gage is pinned at empty even when full. I say this be cause this tractor goes into reduced power mode when the tank is near empty.
any suggestions? Thank you!

I'm not familiar with your particular tractor but in general, if the fuel flow being supplied to the injectors is inadequate then the tractor will have difficulty providing power under load. Have you checked the filter head for clogging of the internal passages? Does your machine have a lift pump and if so is its screen clean? Does your fuel injection pump have a screen on the inlet and if so, is it clean. If your injection pump has a bleed screw, did you bleed the injection pump? Did you find trash in your fuel tank? did you clean the strainer at the tank out let.? Are all your fuel lines in good shape and not pinched? Did you assemble the fuel filter assembly correctly?

 

[AMM]

I'm not familiar with your particular tractor but in general, if the fuel flow being supplied to the injectors is inadequate then the tractor will have difficulty providing power under load. Have you checked the filter head for clogging of the internal passages? Does your machine have a lift pump and if so is its screen clean? Does your fuel injection pump have a screen on the inlet and if so, is it clean. If your injection pump has a bleed screw, did you bleed the injection pump? Did you find trash in your fuel tank? did you clean the strainer at the tank out let.? Are all your fuel lines in good shape and not pinched? Did you assemble the fuel filter assembly correctly?

Thx for all the thought u put in! The fuel flows freely to the lift pump. I tried a replacement filter housing and that did nothing.
My service manual doesnt show a screen at the lift or injector pumps! To re state the loss of power stops if I lift the loader bucket while moving! So if anything lifting the loader bucket would put addtional load on the engine but it works to increas power.. ????
The forward motion pedal gets hard when It loses power?

 

[AMM]

In addition, The tank is Clean and there was not any debri in it. I did fill it with fresh fuel and some 911. the lines are new and not bent. the power returns when I lift the loader bucket while moving forward up hill??? I bled the air at the injector pump . I think I said that in the original post?? Thx again AMM

 

[scdeerslayer]

I noticed if I raise the bucket while losing power going up hill the power comes back until I stop raising the bucket.

That makes it sound like you're dead-heading the hydraulics all the time. I know you said you adjusted the 3 pt but try lowering it just a little to see if that makes a difference. How quickly does the 3 pt fall after shutting the tractor off?

 

[AMM]

I adjusted the 3 pt hitch hyro lever ALREADY. i lower the lever AND MOUNTED A POSITIVE STOP TO PREVENT OVERTRAVEL and and that did help but it still loses power going up hill AND LIFTING THE BUCKET STILL INCREASES POWER ONLY WHILE LIFTING AN GOING UP HILL AT THE SAME TIME??? tHANK YOU FOR THE THOUGHTS! iF U HAVE ANY THING ELSE TO ADD PLEASE DO! AMM

 

[AMM]

tiller drops instantly after shutting down and lower the lift lever. Bucket drops a little slower but it is empty. the landpride tiller is very heavy!

 

[scdeerslayer]

But how fast does the tiller drop after shutdown if you leave the lift lever up? Since this seems to be a hydraulic related issue I'm just wondering if the seals in the 3pt are bad and the hydraulics are constantly lifting the 3pt. Did you try driving with the 3pt lowered a little?

 

[JerryMT]

I adjusted the 3 pt hitch hyro lever ALREADY. i lower the lever AND MOUNTED A POSITIVE STOP TO PREVENT OVERTRAVEL and and that did help but it still loses power going up hill AND LIFTING THE BUCKET STILL INCREASES POWER ONLY WHILE LIFTING AN GOING UP HILL AT THE SAME TIME??? tHANK YOU FOR THE THOUGHTS! iF U HAVE ANY THING ELSE TO ADD PLEASE DO! AMM

From reading all the posts, it appears your problem is more likely hydraulics related rather than engine fuel supply.

Do you have any hydraulic schematics? Your engine power is inadequate when something in the hydraulics causes a large load to occur and lifting the bucket gives the hydraulic system relief, thus allowing more drive power to be available to the wheels. Going up hill exacerbates the problem but is not likely a part of the root cause.

Is there some sort of relief valve in the circuit that is not operating properly?
Is there a priority valve that gives preference to the traction drive that's stuck?
I'm not well versed on hydrostatic drive systems but they are basically a pump and a motor so if fuel flow is not restricted to the engine that drives the pump, than pump load is being increased beyond the design intent.

 

[AMM]

But how fast does the tiller drop after shutdown if you leave the lift lever up? Since this seems to be a hydraulic related issue I'm just wondering if the seals in the 3pt are bad and the hydraulics are constantly lifting the 3pt. Did you try driving with the 3pt lowered a little?

If i leave the lever up the tiller will stay in place for weeks.
The front bucket however will drop on its own over an hour or so.
I tried driving with the tiller up but close to the ground. still in high gear going up hill and sometimes on level ground the tractor loses power until I lift the bucket. starts losing power again as soon as I stop lifting the bucket.
There looks like a hydraulic shutoff and relief valve mounted at the lower mid right and a quick connect is attached to it going to the bucket control valve.
in addition, as i said before when it loses power the drive pedal gets hard to push! runs better in low gear but seems to not be a powerful while digging and loading.???

 

[AMM]

But how fast does the tiller drop after shutdown if you leave the lift lever up? Since this seems to be a hydraulic related issue I'm just wondering if the seals in the 3pt are bad and the hydraulics are constantly lifting the 3pt. Did you try driving with the 3pt lowered a little?

If i leave the lever up the tiller will stay in place for weeks.
The front bucket however will drop on its own over an hour or so.
I tried driving with the tiller up but close to the ground. still in high gear going up hill and sometimes on level ground the tractor loses power until I lift the bucket. starts losing power again as soon as I stop lifting the bucket.
There looks like a hydraulic shutoff and relief valve mounted at the lower mid right and a quick connect is attached to it going to the bucket control valve.
in addition, as i said before when it loses power the drive pedal gets hard to push! runs better in low gear but seems to not be a powerful while digging and loading.???
JERRY, i looked at the drawings , yes there is a relief valve but no priority valve that I can find. I will disassemble the relief valve and clean it then reset it to the same location counting rotations. when I cleaned the internal hydraulic screens one was very badly clogged. I cleaned it and drained all the fluid I added more and drained that as well. maybe I should check the internal screen again? THX GUYS!

 

[scdeerslayer]

Ok, so not related to the 3 pt, but still seems like an issue with the hydraulics. You'll probably need to get the work shop manual to dig into they hydraulic system.

 

[AMM]

I have decided to rebuild the loader control valves and pressure relief valve because it sticks. The bucket maybe dropping because of a small internal lift cylinder leak. I will isolate that as well. i noticed another valve at the hydraulic shut off valve??? thx to all that replied!