Hello guys, I'm working on a Hyster H280HD. In the morning the lift works fine but after using it awhile the lift pressure drops. The owner had replaced the relief valve and the lift pump, when the pump was replaced it work for about a month then started doing the same thing again, thought pump was defective so replaced it again to only get the same results. (Worked a couple weeks then quit again) with the new pump and the mast bottomed out(all the way up) pressure is 3100 psi. Now it's around 2500-2600 changing the relief valve doesn't affect the pressure. Is there a chance he may of gotten a bad relief valve? It was new from Hyster.
Also it has no stored codes in it during all this