Ford van power steering goes out, then comes back.

We've been driving our 2006 Ford E250 a lot lately as we are now living out of it! (I have been thinking about doing a "build" thread, but haven't had the internet access as mostly we've been in the mountains the past 3 weeks.)

A strange issue occurred yesterday: After several hours on the interstate, I braked hard during an exit and all of a sudden the steering effort went off the charts. I figured I'd lost power steering. I pulled over, shut the engine off, and got out to have a look, expecting to see fluid all over the ground from a broken line... except nothing. Checked the PS reservoir and it was full. Hmmm. Confused, I checked everything over in the steering system and saw nothing. So on a hunch, I then started the engine again, and voila, the PS was back! 

Doing a little research, I've learned the brakes and PS systems are connected. I'm thinking about what the best course of action is, and would appreciate input. 

Options:

1. Do nothing until it gets worse? This is my only vehicle and I am hugely dependent on it.  

2. Get the PS system flushed. The fluid doesn't look awful, and is full. 

3. Have the PS pump replaced. Seems a bit reactionary as it's only happened once and it seems like flushing the system could help, but maybe that's the best thing to do. This van does have 313k on the chassis.

Any thoughts?

Hydraulic brake booster? Is there a filter in the system (could be inside or integral to the reservoir)? Could it be starving for fluid in high demand situations?

I would start with new fluid before firing the parts cannon. My daily driver had a similar problem when I used it for autocross. I siphoned and refilled the reservoir multiple times with some Lucas fluid. That seemed to make a difference.
 

I haven't been using it for autocross since,  but will for two events this month. Yesterday I did another drain and fill, then took it into the industrial area and carved it back and forth to see if it would fail to keep up. This time it never dropped boost. 

Sounds like your PS pump could be getting weak. Floating Doc is right, though, definitely drain and fill a few times about 50 miles between, and see how it responds.

Okay, thanks guys, I'll go with the drain and refill method.

O2Pilot, not sure if it's a hydraulic brake booster. 

Thanks all!

This is a long shot, but you know those foil seals they use on PS bottles and injector cleaner, etc? Could one of those or something similar, fallen into the reservoir while adding fluid one time. Maybe the previous owner did it?  The foil falls in, gets sucked by the suction hole and temporarily blocks the fluid to the pump.

We had a customer that was experiencing temporary loss of assist, we couldn't duplicate the problem in the stall. We flushed it and he took it. A week later he's back. We took the pump off and when draining the fluid out came a foil bottle seal. Put the pump back on and he said the problem never came back.

Auto repair, no matter how many years of experience you have, something comes along that no one has seen before.

It's a hydroboost, or at least that's GM's word for it.  The placement of the brake pedal and the required shape of the firewall means that most vans can't fit a big, round vacuum booster.  They instead use power steering fluid pressure to add braking assist.  Been around for years.

I'd go with the flush as well. Ford and GM both don't really beef up their power steering pumps in hydroboost applications and the fluid is doing two jobs.  More frequent flushes are often required as the valves inside the steering box and booster get coked up with hot fluid sometimes.

Thanks Curtis, hydroboost was the word I was looking for. 

And by the way, I love these Continental AT tires your recommended. Great on the highway and great in the dirt!

Awesome!  I love the snot out of mine.  I'm selling the truck they're on, and seriously considering getting some other used rims/tires to put on to sell so I can save these.

What's fascinating to me is I haven't seen another set in the wild. Everyone had the BFGs Falken, and others, but not a single set of Contis. I don't know if people realize how great they are. Thanks again!

Just to follow up, I flushed the system back in Aug '21 and 1.5 years later, the issue hasn't come back. Yay! 

I did notice today that there actually is a big round vacuum booster in there. It's not "hydroboost" after all!

Thanks again. Carry on.

"Several hours on the interstate" means hot and foamy power steering fluid. 

Give it a flush, replace the power steering fluid with Dexron ATF and run it.

If it happens again, try adding a cooler.

Our steering box rebuilder (Steering Solutions in Surrey B.C.) is a very knowledgeable and skilled guy. He swears by ATF in power steering boxes. He says the stuff sold as power steering fluid doesn't lubricate as well and leaks out easier. This was confirmed for me when I replaced the hydroboost in my wife's Suburban. PS fluid made it weep but ATF stayed in.

I switched to Amsoil synthetic ATF and added a big PS cooler to my AE92 to deal with high PS system heat in autocross, and extend the life of its high-enriched unobtanium steering components.

Thanks for the update.

As a follow up to my comment, I ended up using the Ralliart wagon for several events. I did have a slight recurrence of the momentary loss of boost in a slalom after some time, so I repeated the drain and fill which took care of it. 

I recently had the rack replaced in my civic trying to chase down a suspension rattle. Despite having a new rack and fresh fluid, it also had the momentary loss of boost in a slalom. Changing to the Lucas fluid resolved it.