Our 7060 is losing power when cutting hay or brush hogging. I have been told to check the vent lines that come from the fuel tank, we have been unable to locate any line that looks like a possible vent. The tractor does fine as long it is not under a load.
I have an M6060 which has the same fuel system. There appears to be a vent at the top/rear of the tank with a hose that exhausts into a rectangular tube that's part of the cab structure/frame at the left rear side of the tractor.
When an engine runs fine at idle but not under load my first thought is fuel. I've experienced clogged fuel filters and consequent loss of power under load when driving the M1078 600 miles from Seattle to Kalispell. I assume you've done the usual checks such as the fuel filters and water separator?
I have a digital copy of the WSM but the troubleshooting steps only refer to mechanical failures (see below). The manual states "for failures related to the common rail system (CRS), refer to the diagnosis manual (DM) for common rail system engine (9Y120-02440). I have no idea if the problem is something in or related to the fuel system such as injectors, fuel pump, sensors or ECU, but how likely is it that the issue is as simple as a blocked vent? You would think that you could remove the fuel cap and run the tractor under load to see if the cause is a vacuum being generated in the tank.