B7500 Engine Issues, Dies & Surges

[jmpratt]

I have a 2003 B7500 with about 1500hrs. I bought it in 2016 and I use it for mowing and spraying with a PTO powered Arbus 200. Each summer, the kids overheat the engine at least once when mowing in hot weather. Two summers ago, the tractor would lose power if the fuel level dropped below 1/2 tank. A month ago, the tractor was running rough, would not hold set power, dropping RPM toward idle then coming back up. I checked the oil and the crankcase was full of diesel fuel. I assumed the injection pump was leaking so I replaced it. That didn't fix it. Turns out the diaphragm in the lift pump ruptured and was causing the fuel in the crankcase. I replaced it, too.

The tractor is still not holding set power, even with no load. It starts just fine, but will not hold 2000 RPM. If you watch the video in the link, you can hear it surging and falling. The throttle lever is stationary during the entire video but the RPM is all over the place.

After making the video, I tested the compression. Results are, fore to aft: 450, 405, 401. Pictures of the compressions are in the folder, too.

I have removed the tank and cleaned it out. I replace the filter housing and filter. The fuel flows freely to the lift pump. If I crank the engine, the lift pump push lots of fuel to the injection pump. I've check the entire fuel system and I don't see any restrictions or blockages.

I'm out of things to trouble shoot. Any suggestions?

Here's a link to a folder with pictures and videos: https://photos.app.goo.gl/bDcxLJ53fnntNvN56

 

[Russell King]

Did you install the shims between the injection pump and the block that were (probably) there on the old pump?

Look at the springs that are the control between the governor and the injection pump. I assume there are some but that is a different arrangement than I have seen personally.

There is also some “idle apparatus“ on the engine. I have no idea how that works but maybe you can figure it out!

You can get illustrated parts diagrams from Kubota USA dot com or Messicks.

You may be able to get the work shop manual (WSM) for a small donation at this site

www.kubotabooks.com

Over 600 free Kubota manuals. A library of free manuals and parts diagrams compiled by Kubota tractor owners. All free to download instantly. No tricks, no subscriptions, no sign ups, no weird apps or software to install.

kubotabooks.com

 

[D2Cat]

Sounds like it's sucking air in a fuel line.

 

[North Idaho Wolfman]

#1 Shims under the injection pump?
#2 Injector issues.
#3 Valve train issue
#4 Air filter issue.

 

[jmpratt]

The original shims were installed with the new injection pump. It was having the same issues with the original injection pump.

I have not done any trouble shooting on the injectors or valve train

The air filter has been replaced recently and is clean.


Are the compression values of 400 to 450 normal?

 

[mendonsy]

Check all the fuel lines for leaks. My B7500 had a pinhole size leak in the line between the lift pump and injector pump which caused a similar problem. I found it because there was a small spot of fuel on the outside of that line.

 

[jmpratt]

Check all the fuel lines for leaks. My B7500 had a pinhole size leak in the line between the lift pump and injector pump which caused a similar problem. I found it because there was a small spot of fuel on the outside of that line.

No leaks in the lines.

I'm thinking about ordering a set of injectors to see what that does.

 

[North Idaho Wolfman]

No leaks in the lines.

I'm thinking about ordering a set of injectors to see what that does.

DO NOT get amazon, Ebay or any other aftermarket Injectors, they are almost all junk.
Either a kubota dealer directly or Oregon fuel Injection.

 

[BAP]

Did you make sure that the fuel tank cap is venting properly?

 

[InTheWoods]

...Each summer, the kids overheat the engine at least once when mowing in hot weather...

WHY do YOU allow that to happen???

WHO is responsible for cleaning the radiator?

 

[jmpratt]

Did you make sure that the fuel tank cap is venting properly?

Did you make sure that the fuel tank cap is venting properly?

Yes, the cap vents properly. When I had the tank out to clean it, it tested the vent and it worked.