91-92 Vacuum logic diagram? (2 Viewers)

[mct75]

@LS1FJ40, do you still have the VSV for the FPR? Looking at my vacuum lines on the truck, there's an open one where I think this VSV connects. The PO disconnected half of the vacuum lines and looped hoses over the rest. I have a hard start, but once started it runs fine.

 

[LS1FJ40]

@LS1FJ40, do you still have the VSV for the FPR? Looking at my vacuum lines on the truck, there's an open one where I think this VSV connects. The PO disconnected half of the vacuum lines and looped hoses over the rest. I have a hard start, but once started it runs fine.

Not sure. I removed the VSV when I removed the EGR. I followed Spook'a guide to deleting it all. I'm not the most tech savvy person. My 3FE runs smoother now than it ever has.

 

[mct75]

So you removed the brown/red VSV? I think that's the FPR one.

I found some verbage on here and other sites about the purpose of the FPR VSV for similar Toyota EFI systems:

FUEL PRESSURE-UP SYSTEM

The fuel pressure-up system increases fuel pressure slightly on hot restarts for improved starting and idle stability. The pressure rise is accomplished by cutting off the vacuum signal to the fuel pressure regulator. The ECU controls the vacuum signal through the Vacuum Switching Valve (VSV). Pressure rise lasts for about 90-180 seconds after hot restart.

Fuel Pressure Control. The ECU sends signals to the fuel pressure regulator VSV to increase fuel pressure based on intake air temperature, coolant temperature and starting signal. By this system, engine restartability is maintained when the engine is hot. When restarting a hot engine, the ECU increases the fuel pressure above the normal level to reduce the fuel tendency to percolate. This helps restarting and also maintains the engine idle stability.

Operation. When the coolant temperature switch is ON (above 221*F) or higher, if the engine is cranked, the ECU turns on the VSV. As the VSV goes on, atmospheric air is introduced into the diagram [sic] chamber of the pressure regulator and the valve closes the passage. The fuel pressure becomes higher than the fuel pressure under normal driving condition by the amount of the intake manifold vacuum only. Even after the engine is started, the VSV remains on for several seconds.

This pressure-up system in conjunction with the blower fan that cools the intake manifold/fuel rail makes it sound like Toyota was chasing some vapor lock issues.