The reason the valves coming on when you operate it by hand, either via the bleeder plug or by loosening the solenoid is because your allowing the pressure holding the diapahram closed to flow by quickly. Sometimes a valve will not open fully when only the solenoid is loosened, and will also require opening the bleeder. Make sure the center guide rod beneath the valves flow control handle exist, make sure the flow control handle is not fully opened, but just to where turning it down more begins to restrict the flow, then check that all the o-rings, seats and correct solenoid plungers are installed. If a solenoid requires a rubber o-ring, and it's not there, it will allow the solenoid to be tightened down to far, restricting the ability of water to flow through adequately when the solenoids engaged. It could be the wrong solenoid piston(s) were installed, (usually one too long), restricing water flow through solenoid port. You can remove the solenoid and test it at the clock by touching one of the solenoids wires to the common post and the other to the MV Post, then turn the clock on, see if the piston engages fully. You can also remove the solenoid, take a
Sprinkler Marking Flag, or a long narrow rod and see if it will pass through the hole where the solenoid piston seats.
Sometimes a fitting has been installed on the discharge side of a zone valve too tightly, and its threads will partially block the channel where the water/pressure on top of the diaphram is supposed to purge along with the discharge flow. Purchase a new solenoid and test it on one of the valves, if it works, thats the problem, replace them all. Often solenoids are removed without the water being shut off, this allows a rubber o-ring or loose port to blow out without being realized....so it's best to work on valves after shutting the water off, and releaving the pressure built-up in the line.....always disassemble components where any parts that fall can be retrieved...