In every single advertisement, tech spec, etc, the power steering on the 4th gen 4Runner is listed as being "engine-speed sensitive variable assist." My question is: Does anyone know how they are accomplishing this? There do not seem to be any electronic controls on the steering pump or rack, and while there are vacuum lines running to the pressure port on the pump, those seem to be simply to bump the idle up when the steering wheel is turned.

So, does anyone have any idea about this? Or at least a theory? I'm doing a bit of work on the steering and this info would be VERY helpful...

 

Does anyone know for certain what the two vacuum hoses attached to the high pressure power steering hose do? I have heard the same thing that they raise the idle speed when the pressure in the hose rises. But I have not had that confirmed by anyone who can offer a full explanation of the system.

 

your ecu looks at steering angle, wheel speed, throttle position to determine power assist. and its 100 times more complicated with the electric power steering on the new 08 highlanders.

 

How is the power assist adjusted? What does the ECU provide feedback to in order to adjust the power assist? That is; is the pressure and volume to the steering box adjusted? If so how?

 

as far as adjustments goes through the factory scantool, there are none. the only way to adjust steering assist is to have a custom steering rack built with a higher gear ratio. this might be a little too sensitive with a daily driven car tho.

 

I am sorry I did not explain myself well.

In a previous post you said:
"your ecu looks at steering angle, wheel speed, throttle position to determine power assist."

If the ecu determines the power assist, how does it provide more or less power assist under different conditions? I dont see any kind of booster in the steering system.

 

Does anyone know how the power steering assist is adjusted? I understand that it controlled by the ECU based on engine speed, wheel speed, etc. But what I am wondering is what is the mechanism in the steering circuit that actually varies the assist? Is there an electronicly activated pressure valve somewhere in the circuit? If so where is it located?