Manual rear air suspension

I have a 1995 Mazda MPV that was originally made with a nice
auto-leveling rear air suspension. However, it's been replaced with
some other suspension I don't know anything about, nor does the
previous owner, but the auto-leveling computer thing sure isn't
connected to it. There's a tire valve on the rear bumper - I pump air
in, and the body raises up from the rear wheels. 50psi seems to result
in a tolerable ride, though the back of the van is still lower than
the front. Does anyone have a clue roughly how much pressure would be
typical in such a system, and how much it can likely take?
Unfortunately I know nothing about such suspension, and I'm kind of
hoping that they're all pretty much the same for the same class of
civilian vehicle; I've never had a car where I had to manually manage
rear suspension air pressure.

-- Mark

On the pass side front below the WW fluid bottle (that takes more than
a gallon) you should see the ALL pump assy. This pump is controlled
by the valve attached to the frame and rear axle with an elbow link.
Or look at the fuse/relay box under the hood for fuse ALL fuse or
relay.

My guess is the air pump is gone bad or removed and the last guy
wouldn't cough up for the replacement (repair parts are not
available).

Mazda makes 4 rear springs for the MPV. 2 for 2wd - one for the ALL
and one without, and 2 for 4wd - one for the ALL and one without.
The ALL springs are soft and rely on the air shocks to raise the back
end up to level. The pressure used is determined by the load - more
load more pressure.

I replaced the rear springs on mine with springs without the ALL (one
extra coil) from my favorite wrecker. Cost $80. I left my ALL
system intact and it sometimes come on or not, but no longer runs
continuously at 30 below and the rear suspension is where it should be
even when the ALL works or not

pete