I just bought an 01 Tahoe 4x4 from a towing company I work for. Truck had a light roll (driver drove off road and truck tipped onto its roof in the snow). Beyond a broken windshield, its still drivable.

Having a power steering issue. Start the truck, theres a slight power steering whine. There is no power assist at idle. If you rev the engine to 1500 RPMs, there is full power assist for a few moments (15 seconds) and the power assist fades off. If you rev the engine to 2000 RPMs the assist comes back momentairily, then fades again.

Fluid is full. Jacked truck up, operated steering lock to lock about 20 times. Started truck (still on jack) and operated steering lock to lock about 20 times. Shut truck off. Fluid still full, but semi aerated (slight foam). Fluid smells burnt.

Set truck on ground, start engine. No power assist at idle. Rev engine, assist works momentarily then fades. Rev engine higher.....rinse lather repeat.

Removed power steering pump. Replaced with new. Reassembled truck. Jacked up truck, filled fluid. Operated steering (engine off) about 20 times. Set wheels straight, set truck on ground, topped fluid. Started truck, power steering works EFFORTLESSLY to the right (almost turned itself!) Attempt back to the right, no power assist. Shut engine down, check fluid, fluid level OK. Start truck, no power assit. Rev engine to 1500 RPMs, assist works, then fades after 15 seconds. Rev higher, assist works for about 15 seconds, then fades to no assist.

WHAT am I doing wrong here!

 

steering rack spool valve was probably damaged in the roll over. ony way to really test is to install a power steering analyzer and measure pressure for a restriction.