Is it an electronic valve or all hydraulic? Years ago I was having trouble with an IH 800 with electric over hydraulic sequencing. If you changed tractors, those planters had different "pills" for high vs low pressure tractors. Even then, putting fertilizer on it caused more problems, so I just put a toggle switch on it. On/off/ON 3 position switch. Go to the end and just flip the switch. Worked awesome. Great for waterways and planting ends and all that jazz, too.