I don't know which Cummins engine the machine has, but some Cummins engines use a turbo wastegate valve that is controlled by turbo boost pressure. I just have that one more question about the engine I would like to eliminate. That's what allows you to have a machine that can be slinging bucket loads of dirt into a truck very rapidly then in a moment change to a machine that can gently scoop the Robin's nest off the ground that you just bumped out of that tree with your counterweight. As John C described, it gets way more complex when you have to troubleshoot pump/control problems on a forum because excavators have very complex systems. Pump and/or control problem is my inclination as well, but it's too hard to tell without being there hearing/seeing the machine.

You may be lucky though in that most of the component parts such as pumps and electrical components may be used on other manufacturer's machines. That brand of machine is not real common in this country, is usually not well supported, provides little technical information to customers and only parses out that knowledge to their own support personnel as things happen. Judging from your posts I am going to assume you have limited knowledge of the systems on this machine and recommend that you contact a dealer for service. Finally your pump could be mechanically broken inside.ДЄll this is the reason I stated you should hope the problem is in the fuel supply to the engine. The problem can also be hydraulic with plugged passages or stuck control spools. Your problem can be electrical concerning possibly a solenoid, wiring in the form of shorts or breaks or the controller itself. The controller would actuate a solenoid on the pump to change a pilot oil pressure to cause the pump to destroke and relieve some of the flow of the pump and reduce the horsepower demand on the engine. Basically somwhere there should be a speed sensor that will tell a controller the engine speed is dropping. Now what you are describing sounds more like a pump and control problem. At this point I hope the fuel system is the problem. I have also seen the problem that ATCOEQUIP describes. You can get the proper strainer anywhere they sell parts for Cummins engines. I would pull it out and look for part numbers or brand printing. The auto parts filters have paper inside and plug up pretty quickly either when water hits the paper of sludge gets in there. You simply take it out and blow air backwards through it, flush a little fuel or solvent in it and blow again till dry. It is there to catch the big pieces of junk that get in the tank. The issue is that the strainer has a brass screen on the inside and is cleanable. I have seen those strainers taken out and replaced with the filters from the local auto parts house.

It looks exactly like the inline fuel filters that used to be used in cars. There is usually an in line 'strainer' between the fuel tank and the transfer pump on the engine. I'm not saying this is your problem but I have experienced this on several machines that have Cummins engines.

Hyundai excavator troubleshooting