2000 Mitsubishi, change power steering pump and flush system. Cannot get all air out. Zero leaks. I pressurized to 10 psi. Holds vacuum usually. All new hoses and clamps. I have jacked up so front tires off ground and without engine rotation turned steering wheel from lock to lock 40 times. No bubbles coming to top of pump reservoir. Top off fluid,install cap, start engine and zero noise. Go around the block and pump starts making the cavitation noises. What am I missing? It’s getting frustrating

why did you originally change the pump?

rradracer. Intermittent squealing. Ive had my hvac vacuum pump on it, pressurized it, and it start off perfect and zero noise. New belt, new pump, new hoses and clamps, new idler. It holds 10 psi, it holds 15"of vacuum. But it still cavitates itself after 2-3 minutes.

Check for debris or some restriction of fluid into the pump...It sounds like the pump is starving for fluid after it is run for a while...
We had a hydraulic pump that would operate perfectly for a while until some shavings suspended in the fluid would clog a return screen and starve the pump...shut off the pump shavings would settle out and pump would run great until it plugged up again..Aeration can occur during cavitation when there is insufficient fluid.Not sure what your checking for with the Vac Pump.....Hope you find it...

SS Dart.....I was at my wits end and even after it held 10 PSI, I thought might be a rogue air pocket somewhere so i pulled a vacuum on system. This one runs under a vacuum actually. Its blowing my brain!!! Thanks for your time and help.

Hope you find it....There is a thread going on yellow bullet about GM P/S whine....More than one response about using Lucas Oil power steering treatment ....Many swear by it...

I've had it on Fords and tried every fluid and every additive, I surrender.

It’s frustrating when these systems don’t cooperate, isn’t it? Sounds like you’ve thrown everything at it already. Maybe the original pump wasn’t the real culprit, and now you’re chasing a hidden gremlin elsewhere. Could it be a pressure relief valve issue or some kind of flow imbalance in the system? I’d love to hear what finally cracks this mystery!

That’s an interesting angle! Makes sense if something’s intermittently choking the system. Have you checked for any collapsed hoses under load or unseen blockages in the return line? Sometimes even a microscopic tear or internal delamination in the hose can mess things up. Definitely worth taking another close look, especially if it behaves fine initially.

Have you checked Youtube?

Something to consider....most newer vehicles have PCM / BCM controlled variable effort P/S systems, it may require a scan tool to reset the system.