RECOMMENDED METHOD OF LEAK TESTING A FORD OR LINCOLN AIR SUSPENSION SYSTEM
(This method is NOT to be used on '03-Present Expedition or Navigators)
I DON'T recommend it, but the Ford shop manual recommends spraying a soapy water solution on the air bladders and looking for bubbles as the preferred method of leak testing on their air suspension equipped vehicles. While you may get lucky and see the leak using this method, you may not see anything at all unless the leak is fairly severe. This usually leads to an improper diagnosis, unneeded parts replacement and a unhappy owner. In other words, DON'T rule out a leak in the air struts/springs just because you don't see any bubbles!
First of all, the rubber used on the air spring/strut gets dry rotted mostly on the fold of the rubber, or where the rubber folds around on the bottom. This folded area of the rubber gets the blunt of the punishment and dry rots at a much faster rate than the rest of the rubber. Because this area dry rots faster than the rest, this is where your leak is going to be the majority of the time.
The reason the air spring/strut will leak sometime and not others, has allot to do with temperature and most importantly, where the fold of the rubber is. The area of the rubber that's on the fold, will change with vehicle height. In other words, the fold of the rubber will be in a different area while the car is being driven (city height) as opposed to when it is sitting still (vented or parked height). If the dry rotted area of the rubber is "On the Fold", this will expose and open any cracks in the rubber and allow air to escape.
Keep in mind that ALL the air springs/struts have their own solenoid. The solenoid acts as a gate for air and no air should go in or out unless the solenoid is opened up by the module. By turning the suspension switch off, your disabling the solenoids, thus no air should escape....unless of course there's a leak.
RECOMMENDED LEAK TEST
By far, the easiest way to test for a leak, is to allow the car to vent down after shutting off the engine and opening and closing the door.
IT IS VERY IMPORTANT TO MAKE SURE THE CAR HAS LOWERED PRIOR TO TURNING THE SUSPENSION SWITCH OFF, OR THE TEST WON'T BE ACCURATE!
If nothing else, wait 5 minutes after you turn the ignition off...then turn the suspension switch off. The car should have vented by then.
After this, turn the suspension switch off and measure the height of the 4 corners of the car with a tape measure and write it down.
Now drive the vehicle for a few days.
If the vehicle has a leak, the car should go down after driving.
NOTE: Depending on the severity of the leak, it may take more than one day to leak down. This is the case more times than you would think.
By all means, if the car goes down after 10 minutes of driving, turn the switch back and resume your journey. You have answered your question.
COULD IT BE JUST A SOLENOID LEAK?
Its been my experience as a former Ford/Lincoln factory trained and certified technician, that if the solenoid has never been removed before, most likely the leak isn't from the o-rings that seal the solenoid to the air spring/strut. Now if the solenoid had EVER been removed before, the o-rings should have been replaced at that time. If you have an old o-ring that has never seen the light of day and all of the sudden, after 10 years of being cooped up, it is released from tension, it will expand. If reused, it WILL eventually cause a leak . It might take a day, a month, or even a year, but it WILL leak at some time down the road.
In other words, if you replace your air springs, make sure you replace the 2 x o-rings that seal the solenoid to the air spring/strut. If you don't, its not a matter of "IF" it will leak, but more like "WHEN". It would be in your best interest to also replace the little o-ring that seals the air line to the solenoid at the same time. Because this o-ring is AFTER the actual sealing part of the solenoid, if this o-ring leaks, it will only affect the operation of the system while the solenoid is opened, like when the module is making a height adjustment. Not while sitting overnight!
