Dear llama470: there is a fuel pump relay located in the worst possible place Nissan could possibly think of! In the right 1/4 panel just forward of the wheel house. You have your work cut out for you if you want to get to it.
1st remove the sill plate from the door opening.
2.nd remove the trim panel which goes across the roof behind the seat (most 300ZX's are "t" tops")
3rd carefully gain access to the interior 1/4 panel. I gave you these instructions because the plastic gets very brittle and cracks easily when stressed. Anyway, as you remove the panel, just about 1.2 up the 1/4 just behind the door striker is a GREEN relay. That is the starter relay. The relay is energized by the ECM. There is a black wire with a few traces or red dots along the way which will end up going to pin # 108 on the ECM connector. If you ground this wire, the relay should click and the pump should run. Most Japanese cars make and break the grounds, not the positives, so the positive will be hot as soon as you turn on the key. The reason it will start then die, is because the fuel pump has two circuits to run on. One relates to the cranking circuit which will energize the relay and the other will only energize it after the car has started. This was designed so that if the car were in an impact, the impact would kill the fuel pump. NOW, The ECM is what runs the relay after the car has started. you may need to try another ECM.
The fuel pumps are easy to get to on this car. Remove the foam insulating floor covering behind the seats and you will see a large round metal plate with a wire harness going through it. There are quite a few bolts going around the perimeter to retain the plate. NOTE! BEFORE YOU REMOVE THIS PLATE, BE ABSOLUTELY SURE THE PUMP DOES NOT RUN.
Here is another way you can check:disconnect the starter solenoid and with the help of a friend, have them hold the key in the start position. You should hear a kind of shishhhhing sound coming from around the fuel lines. Also, prior to turning the key, pinch the fuel hose where the fuel filter is and you will notice it is easy to pinch flat. If the pump is working, when you turn the key to the cranking position and hold it, try pinching it again. The hose will now fee; some what hard. This would indicate it has fuel pressure, thus indicating the pump is working. Which means is all likely hood the ECM is probably the culprit. Most other components wont keep it from running, it will just run badly. Let me know how you do. Good luck
on May 15, 2019