Fuel Pump not starting in ON position

[mikewags]

Please bear with me, this issue is pretty complex to explain without pictures.

My 300ZX got stolen about 2 weeks ago, the thieves took the wheels and sound system out. They cut away the aftermarket alarm system connections to the battery. I got the car back 2 days later, and put new tires on it and replaced the ignition cylinder (which they had used a screwdriver to start).

All is well, car was running fine for a few days. I stopped to get gas, filled it up - car drove me back to work fine. I went to leave work, car sputtered out and stalled. Couldn't get it started for a few tries, finally got it going again....able to drive a few miles, then the same thing...dies, on the side of the road.

At this point, after a lot of troubleshooting (and determining it wasnt bad gas) - i realized that the fuel pump wasnt making a sound with the ignition in the ON position any longer. Steps I took to fix:

1. Tested Fuel Pump Relay (fine - i hear it click when ignition is ON)
2. PTU is fine I believe (newer style)
3. Fuel Pump is fine (supplied 12 v to it, pump makes sound @ ignition ON position - and car fires right up)
4. Used a multimeter on the connector to the fuel pump, when i switch to the ON position - it gets a brief voltage of 12v

This is the weird part. The connector FEEDING the pump power, signals the 12v when I switch to the ON position (its priming the pump) and when I supply 12v to the connector FUEL PUMP SIDE - you can hear it working : but then when I connect those 2 connectors together, nothing happens at all... Its weird, because the voltage is getting to the connector - and the manual 12v to the pump does make it work via the other side of the connector - but when put together, nothing.

Right now i have the fuel pump wired up to a hacked cigerette lighter charger - the car runs strong like this.

My questions:

1. Based on my research, the 1990 300zx NA fuel pump simply has an ON/OFF setting. So theoretically with it on at 12v at all times, this shouldn't burn out the pump pre-emptively or cause any issues. Is this true? Does the fuel pump controller regulate the voltage to the pump or change the flow of pump to the engine? How it all works now, Turn ignition to ON (pump stays on the whole ride - when i turn the car off - that turns off the cig lighter which powers the pump ... all good)

Will this setup damage the pump or cause any issues? I imagine i'm bypassing the fuel pump controller completely.

2. Any idea why when hooked up to the harness, the pump won't prime; even though I test with a multimeter and see the 12v make it to the feeding part of that connector (under the carpet in the hatch) and the 12v does turn on the fuel pump?

Im thinking some kind of anti theft thing is keeping it from working...but im not sure. Other than that, maybe the fuel pump controller is messed up?

Also, have a computer hooked up to the Z with Consult - no error codes or faults.

Any help would be much appreciated! Thanks!

-Mike

[mikewags]

Other things I did in the troubleshooting process:

1. Cleaned all connectors in engine bay with electrical cleaner and brush
2. Cleaned connections under the hood release near fusebox
3. Checked the Fuel Pump Fuse near the battery (fine)
4. Checked the Fuse Pump Relay near the hood release (fine)
5. Ran diagnostic software to look for an error that might indicate what the issue is (nothing came up)

Know the issue is the fuel pump getting power. And i know the power makes it back to that connector that it hooks up to - its just that I have to manually give the pump power via a hot wire to drive the car. I doubt it's the connector block itself, its making contact... unless i should cut the wires away and bypass the connector part all together.

When i say connector, im referring to the square plastic connector under the carpet in the hatch that goes from the Fuel Pump Controller to the Pump.

I believe this is the wiring schematic:

Ignition - Fuel Pump Relay - Fuel Pump Controller - Fuel Pump

Thanks!