Generator Fuel Pump

It began to fail a few months ago, with a 3-6 code (unknown failure). Took it to a Cummins dealer who started it (after a hard start, as I remember), but it ran for two hours, with them starting and stopping it. Really nothing they could do. Afterwards I ran it myself, I think twice, for 2-3 hours each. Ran fine. Then the next time, ran for maybe 10 minutes, then shut down with a 3-6. Now it'll run for a couple of minutes and shut down, sometimes with a hard start, sometimes not. I've replaced the air filter, oil and oil filter, and I have lots of diesel. I do have 12 volts at the igniter thingies. The Cummins guys said there's not much to do but start tearing it apart and testing things, at $100+ per hour, and it could cost thousands.

When I inquire online about it, the most common response is something fuel related. So I thought I'd replace the fuel filter (looks pretty easy) and then think about doing the fuel pump. I see where it is; just not sure how to get to it. I may call or visit a local Cummins center and get advice.

What puzzles me is how it could run for 2-3 hours one time, and just 10 minutes the next. I could see a fuel pump becoming flakey and acting like that.

Ok, Don, I think I could pretty easily do that hose test. But use what hose? Just buy one that'l fit the input fitting on the back of the gen? Any specific type?

Thanks for any advice guys.

dave