It really sounds like a fuel
problem, i.e. injector, lift pump
, injection pump
, etc. I would continue checking that system before resorting to pulling the engine. The injector can be removed from the engine and the spray observed by cranking the engine, but that must be done VERY carefully as the high pressure spray can drive fuel
into the skin and your blood stream. You say you've tried spraying WD-40 with no luck. Best approach with that is to spray the WD-40 into the engine while the engine is being cranked so the spray is drawn in with the air. You can also try a SHORT shot of engine starting spray, but be VERY careful. Too much and you can damage the engine.