Went to the library to research this a little in Motor ('97-'99 repair manual). According to their application guide, '97-'99 C/K series (includes Suburbans) almost all came with the EVO "speed sensitive" steering system. 3500's and some '99's didn't. So, I'm reasonably sure I have it (for whatever it's worth).
EVO=Electronic Variable Orifice. Basic principle of operation: There is a solenoid on the outlet of the power steering pump that controls a valve. At idle or slow speeds, the valve is full open, allowing maximum fluid flow and, thus, maximum power assist. As speed increases, the computer monitors vehicle speed and another sensor that tells how fast the steering wheel is turning, and sends a signal to the solenoid to decrease the opening of the valve. So at higher speeds you get "less" assist.
That's what I've learned so far. Haven't got any farther other than to climb underneath and visually verify that I can see a solenoid on one of the power steering hoses at the pump.
EVO=Electronic Variable Orifice. Basic principle of operation: There is a solenoid on the outlet of the power steering pump that controls a valve. At idle or slow speeds, the valve is full open, allowing maximum fluid flow and, thus, maximum power assist. As speed increases, the computer monitors vehicle speed and another sensor that tells how fast the steering wheel is turning, and sends a signal to the solenoid to decrease the opening of the valve. So at higher speeds you get "less" assist.
That's what I've learned so far. Haven't got any farther other than to climb underneath and visually verify that I can see a solenoid on one of the power steering hoses at the pump.
