1980 280zx automatic
Car will start and not run well at all only stays running with foot on the gas giving gas flutter

It will only start with the fuel pump “unplugged”
at the floor plug in the rear hatch…. I know sounds odd but true…

Once running (bad) with foot fluttering on gas pedal
If another person plugs in fuel pump it kills car

If you unplug cylinder head sensor the pump will kick on in start up but will flood engine
Same goes for if you un plug the plug on back of the alternator it will kick on pump with key in start and will flood
Once both plugged in and pump plugged in pump won’t come on when start and car will not start

Things I have replaced
1.Ground wire from battery and cleaned other grounds
2.new fuel pump
3.cold start valve
4.cylinder head sensor
5.alternator and tested new one before install
6.checked and tested fuel relays 1 and 2
Under dash passenger side and in engine area
7.EFI relay good
8.opened and checked AFM
9.thermotime switch replaced
10.all new injectors
11.new cap and rotor
12.new plugs and wires
13.oil pan gasket

Any ideas

 

OK, you are unplugging the fuel level sending unit, not the fuel pump. The pump is on the outside of the tank. Have you checked the fuel pressure with a gauge? Install it between the filter and the fuel rail. This engine cant start unless the pump is running. Have you pulled the cold start injector to make sure it is not stuck open? It should only inject fuel for about 8 seconds with or without the engine running. The FSM has the procedure for this. Get the FSM here free download:280zx FSM