1991 Nissan 240SX engine starting

My Sons car wiill not start without squirting gas or ether into the air intake-air filter- hot or cold. After squirting with gas into the intake the engine starts, runs well and strong. So far I have replaced the entire dist, dist cap, rotor, plug wires. Fuel regulator, plugs, We have checked fuel pressure before and after fuel filter-Its good according to the book. I, ve checcked every injector by hooking to the fuel rail pressured with gas via two hoses, and the injectors all squirt gas as they should.