Just like most other Fords & Lincolns,
the air suspension module(brain) on the Mark VIII will test
everything real quick when the ignition is switched to the
on position. If it sees something it can't deal with(something
out of range), it will turn the check suspension message
on and shut down the system. NOTE: While the check suspension
message is on, the system WILL NOT make any adjustments(up
To keep from making any unnecessary adjustments, the module(brain)
will only "look" at the sensors every couple of
minutes or so. When the module "looks" at a sensor,
it will make an adjustment either up or down if needed.
It will make a raising adjustment by first signaling the
compressor relay, which powers up the compressor and pressurizes
all the lines. It will then open up the solenoid(s) on whatever
corner or corners it needs to make the adjustment to and
allow air to flow into the air struts/springs.
When the desired ride height is reached, the solenoid(s)
will close and the compressor will turn off.
It will make a lowering adjustment by opening the vent
solenoid in the compressor as well as whatever solenoid
on whatever corner or corners it needs to make the adjustment
to and allow air to flow out of the air strut/springs, through
the lines, through the dryer and finally through the vent
solenoid on the compressor. When the desired ride height
is reached, all the solenoid(s) will close.
NOTE: The Mark VIII has what is known as a 3 channel system.
This means it only has 3 sensors. One in the left front,
one in the right front and one in the rear. It can adjust
the front individually, but because it only has 1 sensor
in the rear, it adjusts the rear as an average.
The biggest difference between the '93-'98 Mark VIII air
suspension system is that it has 2 different heights....and
the correct height depends on the speed at which the vehicle
When the ignition is first turned on or after the vehicle
drops below approx. 40 mph, it will raise itself to "city
height"....which is good for clearing potholes, manhole
covers & such that is frequently encountered at lower
For '93 and early '94 Mk 8's, the vehicle automatically
lowers to "curb height"....which is almost an
inch at hwy. speeds(approx. 60-65 mph). For Mk 8's mid year
'94 through '98, the vehicle lowers approx. half an inch
at hwy. speeds.
When the vehicle is parked, ignition off and door(s) are
opened then closed, the vehicle will vent once again to
The module is the "brains" of the system. It makes any height
changes necessary based on the data from all 3 height sensors
and the vehicle speed sensor. (Doesn't go bad that often)
This module also handles the EVO (Electronic Variable Orifice)
for the steering. This module is located above the RF kickpanel
and can be seen by lowering the glovebox. The air suspension/evo
module is the one that has 2 connectors going to it. One
is black and the other is gray.
AIR SPRING SOLENOID
Each air spring/strut has an electrically operated solenoid
that the module uses to isolate each air strut/spring from
each other. The module can control the left front, right
front or the rearend independently. The solenoids act as
a "gate" for air. No air goes in or out unless the solenoid
is opened or "signaled" by the module. All solenoids have
a 2 pin connection. Its a simple circuit of "power" and
"ground". The part of the solenoid that holds the connector
looks like a "D" if you look at it from a top
view. To open the solenoid, power should be applied to the
top of the "D" and the negative should be applied
to the bottom of the "D".
The air line is held
in the solenoids by way of a collet. The air line can be
disconnected from the solenoid by pushing in on the orange
plastic ring and pull out on line.
If the module determines
the front or rear of the car should be raised, the air compressor
will come on, the solenoids will be opened up and air is
allowed from the compressor/dryer, through the air lines
and into whichever air struts/spring until the desired height
has been reached. When this height has been reached, the
solenoids will close and the compressor will shut off.
If the module determines
the vehicle should be lowered, the solenoids on whichever
air strut/spring will be opened up, as well as the vent
solenoid in the air compressor. The vented air will pass
out of the strut/spring, through the air lines, through
the compressor/dryer, then to the atmosphere. Once the vehicle
has reached the desired height, the solenoids on the air
springs and compressor will close.
The module is programmed
to only try to raise the vehicle for "up to"
90 seconds. If the vehicle has not reached the desired height
in this timeframe, the module will "time out".
Which means it will turn on the check suspension message
and shut down the system. The vehicle will not try to make
any adjustments until after the ignition has been turned
off, then back on again. Once the ignition is turned back
on, it will then try again for 90 seconds.
The module is also programmed
to only try to vent the vehicle for "up to"
45 seconds. If the vehicle has not reached the desired height
by this time, the module will "time out". Which
means it will turn on the check suspension message and shut
down the system. The vehicle will not try to make any adjustments
until after the ignition has been turned off, then back
on again. It will then try again for 45 seconds.
While these solenoids
don't go bad that often, they do need to be resealed when
removed. Click here for instructions how to reseal your solenoids.
The sensors are the eyes so to speak for the module. The
sensors let the module know the height of the car. These
sensors are attached to the suspension by way of a ball
stud top and bottom. The sensors can be disconnected by
pushing down on the little metal tab and pulling off the
The Mark VIII has what
is known as a 3 channel system. In other words, there are
2 sensors in front and only one in the back. The one in
the back is for both sides as an average. The rear solenoids
are wired together, so when one gets signaled to open, the
other will too. This is why the Mark VIII may sometimes
get out of "kilter" when the car is parked in an unlevel
The compressor supplies air to the air springs/struts. The
compressor on the Mark VIII is the biggest and most powerful
in the Lincoln line. It is mounted in the RF fenderwell.
It has 4 air lines coming out of the dryer which go to each
solenoid on each air strut & air spring. It does
not matter which line goes into each hole in the dryer.
You may find that the lines are molded and one line may
fit better when its inserted in a certain hole, but it won't
make any difference when adding or removing air from the
The dryer is like a common
manifold. In other words, the compressor/dryer assembly
doesn't know what corner(s) the adjustment is being made
on, it only knows to come on when told to do so, or to vent
when told to do so. Again, the module controls that by opening
Any air compressor produces
moisture, so a dryer is needed to trap and absorb the moisture
BEFORE it gets to the struts/springs. The dryer consists
of moisture absorbing silica gel beads and 2 metal plates.
These plates can rust very badly and actually turn to powder.
This powder can then clog up the dryer first and then make
its way to the vent solenoid and clog it up also. So now
what started out to be a dryer problem, has turned into
a compressor and dryer problem.
The dryer is the only part of the compressor dryer assembly
that is sold separately from the dealer.
The compressor is fused
by way of a 50 amp fuse in the engine compartment. Although
possible,it is VERY RARE to see this fuse blown. This compressor
is so powerful, it will actually break the piston rod when
it gets worn! NOTE: When these compressors start going bad,
they will pull allot of amps. This is extremely hard on
the relay! While a relay may get you going again, the compressor
is most likely what took out the relay to begin with. Replacing
one without the other is usually not a wise move.
The vent solenoid on the compressor is used as a "vent to
atmosphere" solenoid. When the module gives the command
to vent the car down, this vent solenoid and whichever solenoid
on the strut/spring that the module needs to vent, opens
up and vents air out of the system. This vent solenoid is
usually one of the first things to go bad on the Mark VIII
compressor. This is due to excessive moisture in the system
that allows the piston in the solenoid to rust and corrode.
The main reason this solenoid has such a hard time with
moisture, is because the compressor is mounted on its side.
If theres any moisture in the general area of the compressor,
the moisture will find its way to the vent solenoid just
from gravity. NOTE: The piston inside the solenoid is metal,
so it can't deal with moisture very long before rust starts
Since the compressor draws allot of amps, it is powered
by a separate relay. On the earlier Mark VIII's, the relay
can be found on the same black metal frame the compressor
is mounted in. This relay is a solid state relay and is
very tricky to test.
NOTE: On the earlier
mark VIII's, you can test the old relay by swapping the
anti-lock relay. IT IS THE EXACT SAME RELAY. If the compressor
goes bad and in turn draws allot of amps, this relay will
usually go bad.
WHAT USUALLY HAPPENS?
LEAKING AIR STRUT/SPRINGS
With age, the
rubber air bladders on the air struts & springs will
dry rott and eventually leak air. The leak will almost always
be "on the fold of the rubber". This is where
the rubber folds over itself and that area changes with
vehicle height. Upon inspection, you may not see any visible
cracks until the height has been achieved where the car
has sat most of its life. Once this area has been found,
cracks will magically open up on the fold.
Early in the stages
of a leak, the air springs & struts will only leak while
being driven. Remember that the system is all automatic,
so if there is a leak, you probably won't realize theres
even a problem until one of two things happen:
#1 The leak
gets so bad that its leaking more air out than the compressor
can put back in.
#2 The compressor
is damaged and can't keep up with the load.
As was stated
before, in the early stages of a leak, it will only leak
while being driven. As time goes on, you will probably notice
the car going down one or more nights in a weeks time. The
number of days the car is down will increase as time goes
the car, the leak will get progressively worse and eventually
to the point where you can't drive the car.
air compressor produces moisture. When a system has a leak
and the compressor has to run 2-10 times more than it would
normally, the compressor will produce 2-10 times more moisture
than it would normally.
In time, the
moisture absorbing gel beads in the dryer lose their ability
to remove the moisture from the incoming air. Moisture is
then able to make its way back to the rest of the system.
Turning every low lying area into a moisture reservoir.
The dryer also
turns into a reservoir for water. In other words, when the
compressor vents, moisture will be blown back through the
compressor. This is very hard on a part that was designed
to be operated dry. These problems include, but are not
of the piston rings, which makes the electric motor have
to work that much harder to do the same job and increases
the heat made by the compressor, which is hard on any sealing
o-rings in the high heat area.
and corroded compressor vent solenoid
and corroded end plates inside the dryer
and corroded intake & exhaust
valves in the compressor
armature & brushes
Because so many
problems start with a leak, I recommend doing a leak test
once a month on any car over 5 years old. This way, you
will find the leak that is only a maximum of one month old
BEFORE it has had a chance to do any more damage.
Click here for the recommended leak test
In my opinion, about
80% of all Mark VIII's will encounter an excessive moisture
problem at one time or another. This is mainly because of the mounting point of the compressor, as it is the lowest point on the system. Just by gravity alone, moisture will find it's way to the compressor.....much less being pushed by high pressure! If you
find out you have an excessive moisture problem, you'll need to replace the dryer every 2 months for 3 or 4 times. In time, it should "sop-up" the accumulated moisture.
The faster you find and repair a leak, the smaller your
parts & repair bill will be!
Author: Eddie Spinks of American Air Suspension