Power Steering Fluid Blowing out Cap??

[Dan15]

Hey Guys,

Kind of an interesting issue that I'm not sure what would be causing it. This is on a 1991 T3 Spirit RT with the ZF (plastic reservoir) power steering pump. After the vehicle sat for about 2 months I started it up and had it idling for awhile. When I went back to move the vehicle it blew out a bunch of power steering fluid, all coming out of the cap. I refilled it and bled out all the air and the pump went quiet again. Drove it for a few miles with no issues, all RPM ranges, multiple WOT pulls and normal turning without any recurrences.

Then I flipped a U-turn which required me to fully lock the steering wheel on the stops, also causing the spike in pressure and it blew the cap off again and sprayed power steering fluid everywhere.... Cleaned it all off, topped it off and drove it around and normal driving wouldn't do anything. Then I took a hard left hand turn on the throttle, not at lock, and it also caused the cap to blow off again... So I came to the conclusion that anytime the steering system is under an extreme load it will blow the cap off but I'm not sure why... With all the power steering fluid everywhere from the 3-4 times it blew out it's hard to tell if anywhere is leaking or just residual fluid but I think the rack might be leaking as well.
Anyone had any issues like this? My current theory is that the rack is leaking and also sucking in air at times, this air gets caught in the system and then under full lock and higher pressures it will blow the pressure out the reservoir??

Any help would be appreciated. I currently have a Reman rack sitting in my garage but I'd be curious to others' opinions before I swap it out.

[crusty shadow]

pressure spring in the pump may be sticking- this would definitely cause the overpressure/cap blowing off issues. replacing the rack wont cure the problem unless it has a leak on the return side allowing it to suck in air.
de-oil the engine compartment and go over the rack and lines with a can of brake parts cleaner- get everything bone dry, run the engine and turn the wheel lock to lock a few times and check for leaks.