Loss of Power Steering Assist Under Throttle - Botched Pump Rebuild / Flow Control Valve Bypass

Suspensionintermediate✓ OP Confirmed

Problem

After having the power steering pump rebuilt by a shop (Driftmotion) as preventative maintenance, power steering assist was mostly present at idle but was lost as soon as throttle was applied. The issue was RPM-dependent, not speed-dependent.

Power steering assist present at idle but lost when giving throttleSteering becomes heavy/unassisted as RPMs increaseNo unusual noises, groans, or whines from the pumpNo foaming in the power steering reservoirSame behavior with PPS solenoid unplugged (heavier steering overall but same RPM-dependent loss)System worked perfectly before the preventative rebuild

Root Cause

The rebuilt power steering pump was internally bypassing pressure. The most likely cause was a weak or incorrect spring on the flow control valve inside the pump, causing it to open and dump pressure whenever engine RPMs (and thus pump pressure) increased, rather than only opening at full lock as designed.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted May 2023 on SupraForums.com