I'm having trouble with my Cat 246D3 Serial number KC601061 losing power after running for several minutes. It has 850 hours. The machine is not throwing any trouble codes. When I first start the machine, it runs normally. At 100 percent throttle, RPMs are around 2560, but that fluctuates a bit. RPMs drop a bit when I move the joystick and move the machine, but will bounce back up. I can run with the two speed engaged, and load a dump truck normally. After probably 10 minutes, the machine starts losing power. RPMs at 100 percent throttle drop down to 2520 without moving a joystick, and after running it for close to an hour rpms at 100 percent throttle can drop as low as 2450 without moving the joystick. The RPMS fluctuate, every time I move the machine and then come to a stop, it could be the same rpm, or +/- 5 RPMS from what it was previously. After probably 20 minutes, I can not operate the machine with the two speed engaged, it will just bog down to 1800-2000 rpms until i let up on the joystick. I cannot run the loader arms and move at the same time without bogging down. It will still operate, just slowly. Today it would not operate my hydraulic buffalo turbine blower at full throttle, it would bog down and run rough. I though this might be a fuel issue so I've done some troubleshooting steps. First, I put on a new fuel and air filter. I read the manual and verified that I have the correct pressure and volume flow coming out of the lift pump. I disconnected the fuel line and pumped fuel into a bucket, and connected a pressure gauge to the lift pump. It passed both tests. I even drained the fuel tank and didn't see any debris. I decided to put a fuel pressure gauge between the fuel pressure check valve and the high pressure pump. The manual says the check valve drops fuel pressure to 1-2 psi. I read 1.25 psi on my gauge at full throttle without moving the joystick at startup, but after a while, this would drop down to 1 PSI without moving the joystick. It would drop down to 0.5 psi or less on my gauge if I moved the joystick. I though maybe the check valve is bad, so I replaced it. The new check valve has 1.5 psi at full throttle and will stay above 1 psi when I operate the machine at startup, but after probably 20 minutes, the pressure drops below 1 psi when I operate and the machine bogs down. I thought maybe the lift pump was getting hot and losing pressure after it ran for awhile, but I disconnected the fuel lines and ran the fuel pressure and volume test while the machine was hot and it passed both. I don't know what other parts of the fuel system could be losing pressure, and not sure what else to troubleshoot. I also saw in the manual that a bad engine speed sensor could be causing the anti stall system to be engaging. Could my fluctuating rpms be a sign of a bad engine speed sensor? I don't notice a change in engine noise when it says my RPM is fluctuating. I also don't know what this engine is supposed to be running at as far as RPMs. This is my first Cat. I'm not sure what else to do at this point, but I would like to exhaust everything before I contact my dealer.
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