S/N: PX17042714 Yanmar 3TNV88F-EPYB Machine has low power, no exhaust smoke concern. When at high idle, engine is 2500 rpm; then when running the boom/arm/bucket cylinders at the end of stroke on relief the machine will drop 300-400 rpm. At high idle traveling or using more then one function machine seems to lack power. Checked hydraulic main reliefs at control valve 3400 psi and 4000 psi overload. Checked for fuel condition, water, blockage in tank. Changed fuel filters. Dealer changed 3 injectors, no change. Put inline sight glass on fuel in going into injection pump, noticed some air. Put sight glass before final fuel fuel filter, no air. Changed fuel filter housing and filter, still notice air. So I ran a from final fuel filter inlet line into a fuel tank to rule out any downstream restriction and no change. At a loss for what is causing this. I don't like the air going to the fuel injection pump. But maybe I am too focused on this concern and missing something else? Exhaust doesn't appear to be restricted, air is certainly not restricted. Machine starts perfectly fine, no misfire. Seems to perk up a little bit more when warm. Thinking about replacing fuel pump, but they are expensive for just a guess. Not sure what other tests to do for the pump. I ran a hysteresis test on the pump and all was good.
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