Why is my lift pump failing?

[blackdogfarmstead]

My 4150 has been experiencing fuel problems for a couple years. It's always the same issue, which begins intermittently; the machine loses power from time to time, only running at low rpm, sputtering, then dies. Usually I can bleed the lines and start her up fine. Then the problem increases in frequency, so that I'm bleeding the lines every day, then every 30 minutes, then every 5 minutes. Then she won't start at all.

Each time the problem becomes severe, I replace the lift pump, and she runs great. I'm on my fourth lift pump in two years now and need to replace again. This last lift pump lasted only 6 weeks.

Clearly, something is causing the lift pump to fail. The fuel lines are good. The filters are clean. There's always plenty of fuel in the fuel filter. I'm pretty sure the problem is after the lift pump and not before. Could it be bad injectors? The problem worsens when the machine is under load, i.e., operating the backhoe or front loader.

I'm getting tired of replacing this lift pump, even if it is only $50.

 

[Billdog350]

I would look at a few logical things. I know there were a few years of Kubotas with bad vents on the fuel caps causing the fuel tank to cave in. If you have a faulty vent on your fuel cap, your lift pump will have to work twice as hard and I can see that causing it to fail prematurely.

If that's not it, do you frequently run your machine low on fuel? Is the fuel fresh and treated with algecide? I have heard of the fuel strainers in the tank getting gunked up, again would cause a vacuum and make it hard for the lift pump to operate.

Lastly, winter use? Could your fuel be gelling and causing the pump to cavitate and wear out?

these are a few ideas you can check easily. If these dont work, report back and I can brainstorm a few more for you.

Oh, another one that was an issue on a customer's JD a while back. The fuel pick up line in the tank was cracked, sucking air, and wouldn't work unless the tank was completely full. After removing the pickup from the tank, adding a new line, the machine fired right up and ran great.

 

[coachgeo]

Do you always buy fuel from the same place? If so, never buy fuel there again. That's a long shot though that only time and a new pump will tell you if bad fuel supplier is the issue.

 

[ShaunRH]

The "Bleeding the lines" part is what has me. Why is air getting into the system?

I'm thinking you have an air leak in the system and the lift pump is working overtime to keep fuel to the injector pump. It's also putting air in solution to the fuel and over night that comes out of solution and makes an air bubble AFTER the injector pump.

It's just a theory though.

I'd be replacing fuel lines and checking all connections for leaks. Also check all housings for cracks and other faults. Air in a fuel system can be almost as big of a problem as water...

 

[blackdogfarmstead]

Thanks for your ideas, guys. I've pulled the fuel lines to check them ... again. This time I did find a small tear under the hose clamp on the supply line just below the tank. I removed the tank and cleaned it, and I removed the fuel cock on the tank, too. Despite having cleaned the fuel tank fairly recently, the fuel cock was pretty gunked up.

I'm off the the Kubota dealer for a fifth (and hopefully final) lift pump and new lines. I think what I'm hearing from you all is correct. Maybe the gunk buildup in the fuel cock is not only causing the lift pump to work overtime but also causing the pump to suck air through the tear in the fuel line.