I have a Komatsu PC40-7 excavator that starts stalling after running for a short while. When using any hydraulics, the engine will lug almost to a halt and if I stop moving anything, it will usually speed back up again; sometimes it will stall. It doesn't happen every time I use the hydraulics and doesn't happen till the machine has been used for a short while (typically 10-20 minutes) and the machine works well till this starts happening. I've changed fuel filters, air filter, oil and oil filter. I'd appreciate suggestions for next steps. Thanks.
Fuel pump would be my guess
I had a Hitachi Ex60 with a somewhat similar problem, it was a clogged fuel line from the gas tank. How old is the machine and when the problem happens, does the machine heat up a lot?
I agree with Wardiker, you've got a fuel supply restriction. Not familiar with PC40-7 myself, so no specific advice. But many machines have screens inside banjo bolt fittings in various locations of fuel supply lines, not sure if Komatsu uses these or not. I've also seen a small plastic inline primary fuel filter in a hard to get to location on PC75 machines. You need to follow your fuel line all the way to the tank to make sure you've found any filters that would cause a problem. If you have any banjo bolt fittings at lift pump or filter housing, remove the bolt for the banjo fitting and look for a screen inside the hollow bolt. If you still haven't found a problem, disconnect the fuel line that comes from the fuel tank and blow back through it with compressed air. Also, be sure and drain any water/dregs from the bottom of your fuel tank.
When was the fuel filters changed last.Just a thought.
Sorry, read over your post again and seen where you had changed filters.Sure sounds like a fuel problem though.
Thank you all very much for your help. The problem was indeed a clog at the fuel tank. Once cleared, the machine was back to working very well. Thanks again.
Yes, makes ya very happy to fix something like that. BTW, did you open the drain on the bottom of the tank and drain water/dregs from the tank? Very important to do that occasionally.