I did a search but nothing really matched my symptoms...

I recently had my PS pump fail (it had a small leak for over a year but finally gave out...constant whine, loss of all PS and hydroboost).

So I replaced the PS pump with a reman from OReilly. It fit fine...was a PITA to replace but everything worked when I powered back up and there were no leaks.

I did execute the purge procedure from the Ford manual (I have the official service manuals) for purging the system (vacuum, cycle brakes, 10 steering cycles, etc) and the system appeared to be fine for about four days.

Two days ago it started whining at startup for about 5-10 sec. So I executed the purge procedure again. Seemed to fix it, but now, after driving for about 15 minutes, the pump will start whining again and PS and hydroboost is affected. The weird thing is that if I drive in a tight circle left and then right, the whining stops and everything works fine for a few minutes. Also, if I hold down the brake pedal hard (actuate hydroboost) the whining stops, which was the opposite of what happened when the pump had failed.

The system still has no leaks and I filled it with a high quality Mercon V (AMSOIL) and purged a gallon after replacing the pump to ensure as much of the old fluid was gone as possible.

One thing I did notice when doing the vacuum test was the the hose from the reservoir to the pump collapses a good bit when doing a vacuum test and that hose is much less stiff than the other hoses. Could that restriction be occurring when the system warms up, causing the pump to be starved during load? I intend to replace that hose today to see what happens but would appreciate anyone's insight into these symptoms. I don't think it is the steering gear as the symptoms are also effected by hydroboost load (brakes) in the same way, so it would lead me to believe it is something common. TIA.

P.S. Looking at the symptom chart in the manual, it lists blockage in the PS reservoir as a potential cause. This wasn't a problem when I disconnected the pump (had plenty of flow from that line...lol) but I'll remove it and check.

 

This job is becoming so time consuming and perplexing...now the system makes no noise and works fine (brakes are noticably stronger) EXCEPT when stopped or a very low speed...then it is like there is almost no PS assist. I troubleshot via the manual and RPM doesn't change it and it specifies a flow rate test (with gear I don't have, of course). I am about to just replace the PS pump again.

What i did:

I removed, inspected, and cleaned the reservoir (no obstructions, no filter), no issues. plenty of flow.

I replaced the hose from the reservoir to the pump. It doesn't collapse under vacuum like the factory one I removed.

I did a flush per the standard DIY procedure (connect to the hydroboost outlet method) and flushed 3 quarts. Only difference is that this time, I used the affordable NAPA-branded MERCON V not the expensive AMSOIL I had put in last week when I replaced the pump.

I did the factory purge procedure, no problems.

So, I suppose it could be one of three things:

1. Replacement PS pump is a lemon
2. NAPA MERCON V sucks.
3. Steering gear has an issue
4. Something else???

The inconsistency of the symptoms is really what throws me. What would you try next?

 

Well, I realize I appear to be having a conversation only with myself but figured I'd close this out. It appears the answer was "#1", lemon PS pump. Replacing the PS pump a second time appears to have restored everything to normal. No whine. Easy to steer at any speed, including stopped, brakes work great. Whew! What a pain this job was...

 

Well, I'm glad you had this conversation by yourself... haha. You provided some good info.

My truck has been hard to steer at idle for awhile now. It's fine when rpm's increase.