trust me, it isn't a "too much fuel because of the fuel pump" issue.
I would bet that over half of the stock 240s you see on the road have walboro pumps in them, because it is cheaper and better than a stock pump.
Shit, I've got a walboro 225 in my car and it is a stock sohc with 175,000 miles on it.
you need to be looking more towards things like the spark plugs, the wires, the coil pack. I'm even starting to get the feeling that it might be compression related, but that would be uncommon because it is a newer motor, unless you or the previous owner never changed the oil...

Taking the line of the rail is only letting there be enough pressure in the rail for one cylinder to fire properly. It is kinda running after that because there is a little bit of fuel in the other cylinders and there is no load.

Have you tried a different rail? maybe the Fuel pressure regulator is bad...
That or the vacuum line that is supposed to be attached to it came off....


actually the more I think about it, the more I think that might be the problem, check that vacuum line and make sure it is on there good and tight. and if you still have all of the emissions and what not, make sure that where that line is getting vacuum is good. there is a manifold thing on the back of the head that supplies multiple things with vacuum from one source, so follow it all the way to the beginning and make sure it is all good.