Intermittent Power Steering (alternatively, how to get a surprise arm workout!)

[LJE]

Hi folks! I've got a good head scratcher for you.

So - (spoiler alert!) I've gotten my '05 LX up and running. However, in the couple short test drives that I've done, I start off with power steering (having bled the system after reassembly), but then shortly lose it. It won't come back until I jack up the front end, turn the engine on, and cycle lock-to-lock a couple times. It's very obvious (even with the wheels off the ground) when it 'catches' and suddenly I have PS again.

Pertinent information:

1. I rebuilt both the rack and the pump with OEM Toyota seal kits. The rack had been leaking previously. I knew this was a gamble...
2. There are no leaks in the system. Fluid level has been very constant. I've also put a pressure tester on the reservoir while I cycled it lock-to-lock (engine off). Pressure stayed good. I did the same thing with a little hand-held vacuum pump - same thing. Vacuum stayed good. Both the pressurized and vacuum levels change if you spin the steering wheel fast (as the fluid gets pushed out of the rack quickly, but takes a second to push it's way through the vane pump), but then they stabilize to the original values once the system has equalized.
3. The pump makes no bad noises, even when I 'have no power steering' the pump isn't whining or anything that would indicate there was air getting to it. Silly question - there's not supposed to be a bolt on the front of the pulley, right? I don't remember taking one off, and the Part Souq diagrams don't show one, but there's a big threaded hole right in the center of the pulley...
4. The reservoir was cleaned out (including the screen!), and many of the hoses were replaced. The main hose assembly that runs from the pump to the rack and then from the rack to the cooler was not replaced as it was not leaking & is expensive.
5. Using Dextron-compliant ATF. Not the preferred Mobil 1 Synthetic, but still the correct type of ATF.

My best guess at this point is that maybe I managed to get some FOD stuck in the rack control valve assembly when I replaced all of those seals, and that FOD is intermittently blocking one of the pressure passages. That's the only theory I can come up with that would make sense as to why it's so intermittent without it sucking in air somewhere or having an obvious leak. I'm considering draining the res & then disconnecting the pump, and then attempting to blow compressed air 'backwards' (through the return line from the rack) while having someone try to turn the steering wheel with the car on the ground. That should flex the rack control valve assembly to open the passages - unsure of if that would work or not, as I'm not sure if the debris would be able to make it's way back upstream.

Interested to hear everyone's thoughts!

 

[LJE]

Following up on this - someone on the UZJ100 Facebook page said that this sounded like my pressure relief valve in my pump was getting stuck open. Sure enough, if I get above 1100 RPM I have great power steering - hardly any at idle though. Verified that the idle up air control valve was functioning correctly, then I tore down the pump again. Once I did that, I remembered that the pressure relief valve plunger felt a little 'sticky' when I rebuilt the pump months ago, because I had struggled to get it out of its bore. The FSM does say that if that plunger doesn't freely move in the bore under its own weight that you should replace the pump.

Sure enough, that dang plunger gets hung up right at the top of the cross hole in the bore that lets the high pressure bypass back to the low pressure side.

The bore and plunger look fine visually - no pitting or anything. I hit them both with some red scotchbrite, cleaned them both well, and lubed/reassembled the pump again. Gave it a shot, and still had the exact same symptoms (no power steering at idle). I took the pressure hose and union back off, and sure enough, that plunger is sitting right at the top of that hole (slightly below where it should be resting. I can easily push it down against its spring and get it to move freely, but it's obviously getting caught under normal operational.

My best guess is that over time, old/dirty power steering fluid wore both the bore and the plunger, allowing the plunger to tilt ever so slightly in the bore, resulting in it catching the lip of that cross hole.

Lexus of Wesley Chapel seemed to have the best price on a new pump - $292 shipped to my door with the sale going on. Hopefully that'll sort out my problem! I'll keep this thread updated.

EDIT: New power steering pump took care of this issue!