1984 300ZX engine stumbles and will not rev

[rondo]

Have a 1984 300ZX Non-tubo. The only way I can get it to run is if I block off the return line, then it will run fine but the idle is erratic. So far I have changed the fuel pump, fuel filter, fuel pressure regulator, fuel injectors and connectors, Mass Air flow sensor. If you unblock the return line the car stumbles and will not rev up and you cannot drive it. The fuel pressure is in spec. Running out of ideas. Please Help Me!

[BadQ45t]

man sorry this forum is so dead, these are not complex engines but the things you changed out are the first things I would have gone after. I would stop throwing parts at the problem and find a mechanic that knows these engines, these were in nearly every Nissan in the 80's and 90s so there are plenty of them out there.