The Basics of a Mark VIII

Air Suspension

DAY IN AND DAY OUT

Starting out in the Mark VIII, you'll notice the compressor coming on as soon as you start the vehicle. This is the air suspension airing up the front and rear struts/springs to bring the vehicle to "city height". City height is needed to help dodge the pot holes and most road debris. If you were to exit the vehicle, this extra air will be vented from the struts/springs and the car lowered back down to "curb height".

The Mark VIII not only adjusts the height of the vehicle depending on weight added or removed, but it also adjusts the height depending on speed. On the earlier models, the vehicle will lower almost a full inch at or around 65 mph to be more aerodynamic. (They changed that to around a half inch on the later models) If you hang around the Mark VIII crowd long enough, you'll hear the term "curb height". Curb height is the lowered height the car is at when driven over 65 mph. This is also the same height it loweres to when you exit the vehicle.

After the vehicle has been driven around 45 mph for a short time, the vehicle will automatically raise back up to its normal "city" height.

THE NITTY GRITTY

MODULE
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 on this.

SENSORS
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 ball stud.

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 area.

COMPRESSOR/DRYER ASSEMBLY
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 system.

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 whichever solenoid(s).

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.

COMPRESSOR VENT SOLENOID
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 setting in.

COMPRESSOR RELAY
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 on the MARK VIII?

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. Clcik HERE for pictures of this.

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 strages 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 on.

Even driving the car, the leak will get progressively worse and eventually to the point where you can't drive the car.

REMEMBER THIS:

ANY 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.

MOISTURE PROBLEMS:

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 limited too:

Swelling 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.

Rusted and corroded compressor vent solenoid

Rusted and corroded end plates inside the dryer

Rusted and corroded intake & exhaust valves in the compressor

Damaged armature & brushes

WHAT CAN BEEN DONE?

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.

You can do a leak test without even getting your hands dirty. click HERE for instructions.

In my opinion, about 80% of all Mark VIII's will encounter an excessive moisture problem at one time or another. This is somtimes caused from being operated in a high humidity area and/or an area that is known for lots of rainfall. Like was stated before, it can also be started from a leak in the system. If you find out you have an excessive moisture problem, you can either replace the dryer every 2 months for 3 or 4 times, or install a SPIDER EXTREME.

REMEMBER, The faster you find and repair a leak, the smaller your parts & repair bill will be!