If the primer pump does not increase resistance. You have a problem. The lift pump valves are marginal at best as they are the reverse check flow valves as well. Usually when they are pretty bad you will see the fuel in the pre filter kind of go back and forth as you pump. Never building fuel pressure basically.

You also could have a marginal relief valve that is open pretty much or really weak on the injection pump.

Or your primer pump has failed. If you see movement of the fuel at all in the pre filter or fuel coming out of the relief valve on the injection pump while pumping it probably still is good.

Anyways from your description something is still wrong and should be located. The fuel system needs attention. Even if it is or is not the current problem. I suspect it is playing into it at least.


There is another diagnostic indicator useable. Since you have the fuel feed lines reversed. If you can get the primer pump to make pressure now. It would indicate your original fuel line supply must have been blocked somehow. The lift pump could not develop pressure because it could suck in no fuel. Long shot but remote possibility.