2000 gs300. I bought it a few weeks ago and it's been super temperamental.

Originally had a code for bad VVTi solenoid, so I replaced that and it drove great with no codes. Then I get a code for lean conditions, cleared that code and kept an eye on short and long term trims, drove fine for 500 miles. Then the fuel pump died so I changed it out roadside. Drove fine for about 50 miles, died again. Crimps came undone. Fixed them properly. Drives great for a week, then suddenly without throwing a code or sputtering, or any noise it just dies at a stoplight.

Get it home. Resistance test pump. .5-.7 ohms. Test plug, getting 12v at the male end. Turn key, no priming, no fuel pressure. Pull pump again. Change filters again, double check wiring, bypass FPC. Still testing good, run a 12v tester to the pins on the sending unit plug. Pump primes just fine, has pressure. Plug back in, turn key, no prime. I can ground blue/white to the chassis and pump kicks on but doesn't stop after a few seconds it just keeps running.

Opened ECU and all resistors/capacitors/etc look mint and good..

What should I check next?

 

To me, it sounds like a bad fuel pump relay. Sometimes relays will not go bad outright. Many I have seen seem to be good then bad then good and then eventually bad entirely.

 

Changed that. Opened ecu and checked everything, looks brand new all around.

I can get the pump to run if I ground the negative on the pump to the chassis (even though the ground through the FPC tests as having the same continuity so wtf) but it doesn't stop priming it just runs all out.

Where does the signal to stop priming come from? It must be the ECU?

These things regulate pressure on the pump hanger correct?

As of now if I were to ground the pump, and throw a switch on the dash for the EFI relay, I could drive it but I don't feel like having it duct taped like that I want to figure out why this is happening.

 

There is a fuel pump computer located in the trunk on the driver side, back behind the liner. That is what truly controls the fuel pump. It is part of the CAN BUS so it does communicate with the ECU, receiving directions for pump speed (slow RPM = slow pump speed, fast rpm= fast pump speed). I've heard of this computer going bad a couple of times. You can buy a used one from anywhere between $20-70, part number is 89570-30180. A bad fuel pump computer may do something similar to that.

 

I have bypassed the FPC entirely and it doesn't change anything

 

Not sure then, I know I thought my fuel pump/FPC went bad when my car wouldn't start. Turns out the previous owner (whom I had just bought the car off of) didn't have the coil wires properly attached. I was getting igniter fault codes. Igniter fault codes tell the ECU to stop priming the pump, or rather to not let it run at all. Check for pending codes, if there is none then I would suspect there would have to be something up with the ECU. Remember that these cars will throw codes when you restart the car, with some exceptions (I.E a sensor being unplugged, which will throw a code right away
)

 

I am wondering if maybe my FPR is dead and maybe it's just not holding pressure so it won't kick off?

 

Could be, if you still have your old fuel pump, try swapping it again. Sometimes aftermarket fuel pumps are built with el cheapo quality. I believe the fuel pressure regulator is inside the pump itself, I think they used it for the Venturi jet pump system to suck fuel out of the other side of the tank. So in other words it's a returnless system

 

Do you have a brand and part number for the new fuel pump? The GS 300 has a unique pump that isn’t interchangeable with similar vehicles like the GS400 or even an SC300. If u had to purchase it in an emergency then it’s possible that u were sold a pump that’s not compatible.