How I fixed a power steering problem that drove me nuts.
On the last 2 MK4's I built I used the Vintage Air front runner system with alt., A/C and P/S. On my MK4 with my 347 I had zero problems at all. On my customer 427 build we had 2 problems. A P/S leak at the pump and twitchy steering felt by customer. I use the P/S rack from FFR and the hoses they send in the kit. (90 Mustang 5.0 w/o A/C for the P/S hoses) It turns out the P/S pump is from Detroit Speed and can have a 2gpm or a 3gpm pressure valve. Unfortunately the 427 came with a 3 instead of the 2 it should get for the Ford rack. Also the valve was not machined deep enough for the mylar o-ring to seat and seal the pressure hose fitting. I was able to install a aluminum washer that made up the difference. The end result is no leaks and better steering feel all around. I hope this may help someone down the road. As I pulled what little hair I have left out trying to fix this.