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Lincoln Mark VIII
Air Suspension in General
Just like most other Fords & Lincolns, the air suspension module(brain) on the Mark VIII will test everything 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. To keep from making any unnecessary adjustments, the module 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 air suspension compressor relay, which powers up the air suspension compressor and pressurizes all the lines. It will then open up the solenoid(s) on whatever corner it needs to make the adjustment to and allow air to flow into that airbag. When the desired ride height is reached, the solenoid(s) will close and the air suspension compressor will turn off. The system makes 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. This allows air to flow out of the airbag, through the lines, through the dryer and finally through the vent solenoid on the air suspension compressor. When the desired ride height is reached, all the solenoids will close and Lock In the air. 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 and other Fords/Lincolns, is that it has 2 different heights. The correct height depends on the speed at which the vehicle is traveling. 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 speeds. When the vehicle is parked, ignition off and door(s) are opened then closed, the vehicle will vent once again to curb height.
The module is the brain 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 kick panel 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.
Each airbag has an electrically operated solenoid that the module uses to isolate each airbag from each other. The module can control the left front, right front or the rear end 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. It's 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 vehicle should be lowered, the solenoids on whichever airbag will be opened up, as well as the vent solenoid in the air compressor. The vented air will pass out of the airbag, through the air lines, through the compressor/dryer, then to the atmosphere. Once the vehicle has reached the desired height, the solenoids on the airbags and air suspension 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.
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.
The compressor supplies air to the airbags. The compressor on the Mark VIII is the biggest and most powerful in the Lincoln line. It is mounted in the RF fender-well. It has 4 air lines coming out of the dryer which go to each solenoid on each airbag. 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 it's 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 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.
Any air suspension 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 air suspension compressor problem. The dryer is the only part of the compressor dryer assembly that is sold separately from the dealer.
The air suspension 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 suspension 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 air suspension 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.
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 air suspension compressor is mounted in. This relay is a solid state relay and is very tricky to test
WHAT USUALLY GOES WRONG? Early in the stages of a leak, the airbags 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 suspension 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 on. Even driving the car, the leak will get progressively worse and eventually to the point where you can't drive the car.
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 intake & exhaust valves in the compressor
Damaged armature & brushes Nobody Has a Better
Lincoln Airbag or
Lincoln Mark VIII Air Suspension Compressor
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WHAT CAN BE DONE? Due to the replacement parts on the Mark VIII getting harder & harder to come by, we recommend doing an air suspension conversion and be done with the problems forever. This air to coil spring conversion kit is the perfect solution to your Air Suspension problems. Converting to a conventional coil spring suspension is much more affordable than the air, as the cost of the 4 Wheel Kit is less than replacing 1 Front Airbag!