Fuel Pressure Dropping

[Nomu]

Hi everyone, I'm seeking advice with a fuelling issue. My fuel tank had a leak and i took my car(1990 r32 gts-4) to a mechanic to get it fixed up. He fixed the leak and replaced my lines since they were old and cracking. When driving home, when coming to a stop my car would just drop to 0rpm and stall. I took the car back to him and he said i had a bad fuel pump and replaced it. I got my car back, but now my car was idling at 1400-1500rpm. I got home and saw that he had unplugged my TPS, and so it was just going on the fall back system and idling around 1500rpm. After plugging the TPS back in, the car had the same fuel pressure issue. I put a fuel pressure gauge in and when turning the ignition on, the pressure goes up to around 50psi. When i start the car it backs off a bit, down to around 35psi and then just slowly drops to zero and stalls. 

Does anyone know what this guy could have done or has anyone had this problem before? Just looking to know what I should be checking first. 

[niZmO_Man]

Wow hope you don't go back to dodgy mechanic.

[Ben C34]

14 hours ago, Nomu said:

Hi everyone, I'm seeking advice with a fuelling issue. My fuel tank had a leak and i took my car(1990 r32 gts-4) to a mechanic to get it fixed up. He fixed the leak and replaced my lines since they were old and cracking. When driving home, when coming to a stop my car would just drop to 0rpm and stall. I took the car back to him and he said i had a bad fuel pump and replaced it. I got my car back, but now my car was idling at 1400-1500rpm. I got home and saw that he had unplugged my TPS, and so it was just going on the fall back system and idling around 1500rpm. After plugging the TPS back in, the car had the same fuel pressure issue. I put a fuel pressure gauge in and when turning the ignition on, the pressure goes up to around 50psi. When i start the car it backs off a bit, down to around 35psi and then just slowly drops to zero and stalls. 

Does anyone know what this guy could have done or has anyone had this problem before? Just looking to know what I should be checking first. 

So the car has proper fuel pressure when the tps is unplugged?

[Nomu]

When the car is being revved there is fuel pressure. So i can drive if i just keep tapping the accelerator, the pressure jumps back up each time i open the throttle at all. But as soon as i stop, the fuel pressure just drops and the car stalls.

[GTSBoy]

This makes no sense.

[Ben C34]

Yep. Something pretty weird is going on

[Kinkstaah]

Feels tune-y. But nothing should have changed after replacing a fuel tank.

[iruvyouskyrine]

More information.

What ECU? What fuel pump? What injecotrs/rails/lines/filter? What were you using to measure fuel pressure and where were you tee'ing it into?

And get a new mechanic.

[Nomu]

Everything is stock. The fuel filter is just a RYCO z387 and the pump is a wallbro 450. 
Was using a stock standard pressure tester gauge and tee'd in just after the fuel filter. 

[Ben C34]

Oh, the walbro has likely melted stuff.  Look up how to do a direct wore for the pump or more stuff will melt.

[KiwiRS4T]

10 hours ago, iruvyouskyrine said:

And get a new mechanic.

What he said⬆️⬆️

[89CAL]

The fuel pump control module has likely failed. When the car drops back to idle it is supposed to drop the speed of the fuel pump to prevent excessivly circulating fuel. Sounds like the low side is playing up

Direct wire your fuel pump through a relay as suggested