deere 270D excavator. What tests can I perform to check if the Main hydraulic pumps are performing as intended

The best way to judge the 270D pumps is flow under load, not pressure alone. A worn pump can still reach relief pressure briefly while producing poor flow.

First checks

1. Warm the hydraulic oil fully, then verify engine speed reaches rated high idle. Check oil level, suction strainer, tank breather, and the large suction hose for collapse or air leaks.
2. Connect a calibrated flow meter and pressure gauge to each main-pump delivery test port. Test Pump 1 and Pump 2 separately, then together if the manual provides that procedure. Keep the oil temperature and engine rpm recorded.
3. Compare measured flow with the John Deere D-Series specification. The 270D LC uses two variable-displacement pumps, each rated at 236 L/min, 62.3 gpm, with implement and travel system pressure listed at 4,980 psi. These are rated specifications, not guaranteed readings from an 11,000-hour machine.
4. Check pressure while slowly stalling a function, such as arm-in or bucket-curl. A pump that reaches near relief pressure but has low flow is worn internally. A pump that cannot reach pressure may have a failed regulator, control signal, relief valve, suction restriction, or major downstream leakage.
5. Compare the two pumps. If one delivery pressure or control pressure is abnormal, isolate that pump and its regulator. The 270D monitor service menu can display pump 1 and pump 2 control and delivery pressures, which is a useful comparison before disassembly.

Also check pilot pressure and the load-sense/control circuit. Low pilot pressure or a restricted signal line can make both pumps appear weak. Do not open test fittings until the tank and hydraulic lines are depressurized. Add the serial number, oil temperature, engine rpm, and individual pump flow and pressure readings for a sharper diagnosis.