I have a 341 excavator and the pilot pressure drops....

[marsatp]

I started having trouble with the controls running slow and with no power. So I bought a service manual and it shows where the test port is and says there should be 400 psi on the port. After running the maching for a while the pressuer will drop to 200 psi and the controls are basically useless. Everything runs slow but it wont swing at all. I talked to the dealer and his answer was bring it in. the blade runs off of pump pressure with a cable control and it has never lost power. So I think the pump is ok.

 

[mrmikey]

I'm not familiar with your machine but I've worked on a few variable displacement, pressure/flow compensated pumps (Rexroth) for running plow trucks, I'm not an expert by any means so consider the source . We had a somewhat similar problem with a two year old system and it ended up being the compensator valve. Refering to the system I worked with there are two adjutments, the high presssure (2KPSI) and the low or standby pressure, that is the 400psi that gives you the signal pressure to move the cartridges on the end of the valve which in turn move the spools. There are two independant cartridges in the one compensator body, one for each setting. Ended up, if I rememeber correctly, there was a bad 'O' ring ' 'bout the diameter of a dime that had a small tear and theory was once the oil warmed up it was allowing it to bypass.

Another scenario we had although this was on a new installation. The system would work for a couple of minutes but it would get slower and slower reacting. Shut the unit off for a couple of minutes and she'd be good to go for another few minutes. We took a pressure reading at the compensator which is attched to the pump, 400 psi all was good, took another at the signal line where it went into the valve bank and 100-200 psi, wtf..... Long/short of it, there was a bad crimp on one of the hydraulic fittings and there was a flap of the inner liner going over the end of the crimp fitting acting like a check valve.

Hope this helps a bit.......Mike