The customer complained of low power/ground speed.
Most hydrostatic machines like this have some form of load sensing which will automatically monitor engine speed and reduce the hydraulic demand to prevent engine overload. This makes machine "power" issues difficult to diagnose as the engine always runs, by design, at or close to it's rated RPM.
First thing we tested was engine RPM at full load. The machine was immobilised and the brakes locked on. Rated speed was low by around 20 RPM. Not low enough to be conclusive either way and the engine sounds OK with no missfiring of rough running. Next we tested the various transmission pressures. All were good and the underspeed circuit (which controls the engine load) operating correctly.
This takes us back to the engine. We need to test fuel transfer pressure next so a gauge is installed in the pump fuel gallery; with the engine running the gague reads zero. That can't be right, it must be faulty. Let's try another gauge. Still zero. We stripped the fuel transfer pump and sure enough, every valve in the pump was damaged. This engine had been running on gravity fed fuel, and it didn't sound too bad..... I'm amazed it actually ran at all. Especially as the fuel tank was pretty much on the same level as the engine.
The transfer pump was rebuilt, fuel pressure was now up to spec and the machine up to full power.
