PRVR Solenoid

The Pressure Regulator Vacuum Relief (PRVR) Solenoid is a solenoid valve that controls vacuum pressure to the fuel pressure regulator.

A stock PRVR Solenoid. Image courtesy of Robo's Site (twinturbo.info).

Function

The PRVR Solenoid is used exclusively during startup on the Z. It's description, per the Factory Service Manual, is as follows:
The solenoid valve responds to the ON/OFF signal from the ECU. When it is off, a vacuum signal from the intake manifold is fed into the pressure regulator. When the control unit sends and ON signal, the coil pulls the plunger downward and cuts the vacuum signal.

In short, the PRVR Solenoid raises the fuel pressure under certain conditions. It is believed that it was implemented to prevent "vapor lock", a condition that plagued early 240Zs, but is practically unheard of on modern fuel injected cars. The PRVR Solenoid is controlled by the ECU, which uses the fuel temp sensor to determine its desired state.

Bypass & Removal

A faulty PRVR Solenoid can cause hard starting, especially when the engine is hot. To simplify the engine bay and vacuum system, many opt to outright remove the PRVR Solenoid and its associated vacuum subsystem. There are practically no ill-effects to this procedure.
Images courtesy of Robo's site.

1. Remove the two 10mm bolts securing the fuel filter bracket to the frame. The solenoid and bracket can then be lifted up and removed from the car.
   
2. Disconnect the vacuum lines and electrical connector.
3. Install a new vacuum line connecting the Fuel Pressure Regulator directly to the intake manifold.
   
4. (Optional) With the driver's side fender removed, the vacuum canister for the PRVR Solenoid can also be removed. (Red X).