The case against
The feed pump inside the injection pump can pull up to 54 litres an hour,a 1HZ or 1HD T will only use 12-25 litres an hour,any more and your egts would be through the roof.
I cant see the logic in how it will take the load off the feed pump.The feed pump is running off the main shaft inside the injection pump and spinning all the time.It has 4 vanes that that pick up the fuel and pressurize the inside of the pump to about 7-8 psi.
As wear develops in the feed pump,the spring loaded vanes move down to take up the wear(at least thats my understanding)
The feed pump will usually outlast the other components inside the pump.The only ruined feed pump I have seen was one that had some moisture inside it and after a period of non use it corroded the bottom of the feed pump.
I had a totally worn out fuel pump rebuilt a few years back.It had nearly every major component replaced ,except the feed pump.
If you add any extra pressure to the inside of the pump ,the regulator valve opens up more and sends it back to the tank.
The regulator valve is designed to cope with all viscosities of fuel at all temperatures.
So if the fuel is warm and thin(flowing fast),it will send more back to the tank.If the fuel is thick or cool(flowing slow) it will send less.
If you are not getting enough fuel into the pump,then you need the regulator valve adjusted.
Ive yet to meet anyone in Australia that uses one.There is an owner on one of the east coast forums who jumps up and tells everyone to install one when they have fuel starved engine,but owners looking for real answers have found blocked fuel lines or fuel switch solenoids not working correctly.
Or more commonly,that their pump needs a rebuild.
If your fuel pump appears to be losing pressure at high speed which is normal for a rotary pump with high klms,nothing will help it except a new plunger/and or distrubutor head.These components are compressing fuel to 1800psi and a 5 psi pusher pump will not improve that .
Someone mentioned that Toyota increased the diameter of the fuel lines.This is true,but it was more likely to increase the flow through the fuel pump to keep it cool.One theory is that the early fuel pumps were getting too hot causing some of the components to expand and cause excess wear in the fuel pump.
But Toyota has never released an explanation for that ,so it is all conjecture.
I am still trying to find a real documented case of a pusher pump actually helping a rotary pump that is in good condition.