Customer bought an EX300-3 that's got a weird glitch. When you first start it cold it will operate fine for a couple minutes and then you lose everything on the 5 spool side of the control valve. Left track, swing, thumb ect. everything off the rear pump. If you shut it off until the battery relay clicks off, restart it, everything works again for a few minutes. If you shut it off and restart before the relay clicks off the problem remains. After about 5 times restarting it the machine will run fine for the rest of the time. Since you have to wait for the relay to click off, removing power to all electrical components, it would seem like an electrical problem but I can find nothing that that would effect just the 5 spool side or just the rear pump. Temperature also may have an effect on it although just starting it and letting it warm up doesn't change anything, you have to operate and restart it several times before it wants to work. There are also no codes being set. I've spent a fair amount of time in the manual but haven't had a lot of time to dig into the machine. Any thoughts would be appreciated. Thanks.
I suspect intermittent rotary group valve plate lift/separation at the pump cylinder head. Check the flow sense pressure at the rear pump. Under normal conditions,when fully stroking a spool on the 5 spool side the flow sense pressure will be approximately 85 psi. With pilot controls in neutral ,flow sense pressure will be 300+/- 60 psi. If and when the valve plate is actually separating from the cylinder head there would be very little oil flow through the control valve neutral passage so flow sense pressure would be very low with pilot controls in neutral.
I've seen the same thing as well in the past on that size of machine. The customer and I went round and round about the cause over a couple of days when he left the area. I pumped down the hydraulic oil in the tank and pulled the end off the pump and the scratches and scrapes on the brass valve plate became readily apparent. They bought a new valve plate and lapped it against the barrel assembly and put it back together. Thing was still working a year later.