Hi guys, just purchased an '86 Z31 turbo and discovered that the fuel pump runs constantly with a "thumping" noise. The car runs fine but I thought that the pump should stop running when correct pressure has been reached.
How constant is "constantly"? Does the fuel pump run when the key is Off?
If so, then yes, I vaguely recall the problem here a while ago where it sounds like the fuel pump shield had continuity with the pump motor ground, requiring a replacement pump.
The pump does not cut off when the "pressure is reached". The ECU runs the pump for about 5 seconds when the key is turned to On and knows nothing about the pressure. The ECU can only assume that the FPR is working correctly. The ECU would still turn the pump on and off if the FPR was sitting in your pocket and fuel was gushing all over the engine.
The pump has its own overpressure limiter in case of some fuel system failure but that should rarely if ever be needed.
As for the thumping noise, no idea. Maybe some klutz has put a non roller-vane pump in it.
"The ECU runs the pump for about 5 seconds when the key is turned to On"
Mister_T - if that is the case, what is the solution? When I turn the key to the On position mine does not shut off after 5 seconds. It does stop once the key is in the off position but otherwise runs full-time.
The ECU controls the ground to the fuel pump. When the ECU wants the pump to run at below battery voltage, the ECU handles the ground for the fuel pump itself. When the ECU wants full battery voltage to the pump, the ECU triggers a relay to ground the fuel pump.
On the assumption that the wiring is all to spec, you would replace the ECU if it fails to control the pump correctly.