My wifes Navigator is kicking my ass...

So the power steering has been acting up for a while. It would go out every so often and come back, especially in the neighborhood. This continued for a while till I finally I ended up getting a new power steering pump (W/ PULLEY) and swapped the pump out. Problem solved, right? Nope. Not only is the problem still persistent but now it's actually maybe worse. When turning now the power steering will kick in and out making smooth steering impossible. And this is very inconsistent so there is that. Crazy thing is, standing still you can row the steering wheel back and forth and it seems to work great. Before I swapped the pump it almost acted as if the belt or the pulley was slipping on the shaft. Now it also feels like it's having a seizure on top of that.

Has anybody had a steering rack fail like this? I thought maybe the speed sensitive steering sensor was acting up but online research doesn't seem to support the fact that the thing actually has one, so that one is out. I'm out of ideas....

TIA.

Belt a bit too long?  Tensioner pivot seized up?  

4wd? Outer CV joint broken?  

diverter valve in the steering box

Yeah, this problem is going to be in the steering gear (gearbox or rack&pinion, whichever you have) itself. 

Cool, thanks for the feedback guys. I've never had a steering rack fail. 170K miles is a little early in my book.

I think I know your problem because I just fought with similar symptoms in a F150.  Would feel as is pump was cutting out, but it was also difficult to get the wheel to return to center at times.  The lower u-joint in the steering shaft was failing (thanks Ford and roadsalt).  Would drive fine one day be damn dangerous to steer the next. The lower section of the shaft with two joints is available for $150- $200 and made the truck steer better than I ever remembered.  Must have been a getting worse for a while.

Smartass alert!!!!

Its a ford. They circled the problem for you!

Really, it sounds like either a bunch of binding in the steering linkage, or a bad pressure balve in the hydraulics.

Have you jacked it up on stands and tried to isolate the two systems? Engine off, see what it feels luke, paying attention to the amount of force needed at all points to cycle from lock to lock. Also look for play in all components. Ive had udler arems go bad and do exactly what youre describing just before catastrophic failure. 

My mom had a 1984 Thunderbird that would feel like it was in a heavy wind all the time. She had the entire power steering system replaced with the Motorsport "high effort" (5.0 Mustang) stuff, still had the problem. Then one day, she was leaving the dealership where she worked, and  the tie rod fell off the steering knuckle. Seems like they should have replaced the tie rod ends when they did the rack.

On edit: My "spare 'Mont" ('81 6-cylinder sedan) actively resists going right until the fluid gets warmed up. I know it has a sticky valve in the rack.