1991 lexus ls400 power steeing slowly got hard to

best ask a steering specialist shop as the engine identification shows a es300 as a 1mz-fe (3.0 ltr) and a ls400 as a 1uz-fe (4.0 ltr)
there may be mounting differences between the engines

Steering gear(aka Rack and Pinion) look for leaks at the bellows boots over the inner tie rod ends.

Here's how to bleed the power steering. Repair Guides Power Steering Pump Bleeding AutoZone com

this problem indicates a bad steering rack. the bushings in the rack are worn and have caused groves in the housing causing the binding. the only solution is to replace the steering rack. if a problem was the power steering pump it would not get easy when you turn the steering wheel further the problem would be there all the time.

You can get a dye to put in the power steering reservoir it makes the fluid glow

The main purpose on an alternator is to recharge current back to the battery. One of the most common problems with the Lexus LS400 and SC400 is that power steering pump seal leak. Right below the power steering pump is the alternator. The power steering fluid will drip down and cause many electrical problems for the alternator. Therefore, its very common to have the alternator go bad along with the power steering pump, just be sure to check.

Hi,
Both your Van and your Lexus have power assist steering. So the "feel"
will be somewhat different. How quickly and easily the "Assist" helps varies. The Lexus is an Luxury car.It is designed to make steering easier.
Less effort needed by you turning the wheel to turn the car. So you were right in your diagnosis. The Van will have a heavier feel.
Enjoy the ride.

Check out the 2 lines that run from your power steering pump. With the engine running try moving them, and look for fluid leaking around the end of the hoses, you will probally find one of them leaking at the fitting. Of course be careful with the engine running, do not have any rags or anything in your hands around a running engine.

may need a code put in for the computer to work

There is a loud squeak on the front of my 1991 ls 400. The squeak is near the alternator. Any one no what it is?