I need some help and clarification on my understanding of the LLS system on my 1997 Eddie Bauer Expedition.
Over the last week, the left rear drops when the truck is parked. In only about a few minutes time. The right side drops somewhat. Upon start up, everything rises back up the way it should.
I have checked and found the following:
Very slight leak at the Line Union by the Master Cylinder when the truck is running and the LLS system switched on. My understanding is this would normally cause both sides to drop if the system is switched on and calls for air. New Union in hand and going in tonight.
With the system pumped up and I turn off the LLS switch, there isn't any air leaks at the Union, even with the Union disconnected. I assume that this means the solenoids are still electrically sealing? The left rear still leaks down fairly rapidly.
If I start the truck and power up the LLS system, I get air out of both lines at the Union. One from the pump and the other from the rear. I assume that is because the solenoids have opened and it is relieving the air from the good side.
My best guess as I can't get under it to soap test it fast enough is that the left Air Bag must have a hole, or the solenoid seals at the bag are gone.
Can some one verify this understanding and conclusion for me as I don't want to order more or less parts than I may need? I have seen where it is stated that "if the truck drops with the LLS system turned off, then you have a leak". I assume this means "on the air bag side of the solenoid", but I may be wrong.
Thanks in advance for any and all help.

 

2Wd or 4WD?

Rear only LLS or 4 corner LLS?

Depends on how bad the union is leaking. It prolly just takes the pump longer to level out the rear. Could possible cause the pump and/or pump relay to overheat.
If the leak was so bad that the pump couldn't overcome the leak, yeah, the back end would go down, but the pump would never shut off.

With the LLS switched off, all the solenoids are off and closed, as is the pump, so there would be no air passing through the union. The left rear droops because the left rear air spring and/or left rear air spring solenoid is/are leaking air to the atmosphere.

Both lines have air because: the air from the pump has air becasue the pump is running. The line going to the rear has air coming out of it because the rear air fill solenoid is open trying to accept air, but since the union is open the rear air is just blowing out that line.

By the time you get under it, it will still be leaking a little. Or you could spritz it down with soapy solution, turn the system on until it pumps up, turn it off, and slide under there and see where the bubblies built up.
(I like to drive the rear tires up on a couple of 2x6 scraps - that lifts the rear axle up a couple of inches so it is easier to slide under it to view all the way around the air spring.)

 

With the suspension switch turned off there will be no electrical signals to the solenoids and the truck should stay raised indefinately. From what you describe I would suspect the solenoid O-rings on the side that drops. It will take a bit of doing to do the soapy water test on it as it is up high and in a difficult to reach location. I suggest that you buy new O-rings from Ford for both of the rear the solenoids and replace them after you do the soapy water test on the air bag itself. Some others have posted that they have changed the O-rings with good results.

 

Thanks guys for the prompt help.
pdqford, Sorry about my short-sighted description, It is 4x4 with 4 corner LLS.
It seems that both you and Moto Mel have confirmed my understanding of how the LLS system works and my conclusion that the problem is either Solenoid O-Rings or the Air Bag itself. I guess my next steps will be from underneath it. I'll keep all notified of progress and resolution to maybe help others in the future.

 

Here's a bit of an update.
Found the left air spring to be leaking out through the top cap. I sprayed everything down with soapy water solution and was focusing on the solenoid seals, but found bubbles coming out between the plastic spring cap and the top spring mount. Wondering if this is a common failure area? I am now convinced I need new air springs. Dealer quoted special order @ $573.00 each. OUCH! Has anyone had good luck with the aftermarket springs from the suspension folks on-line?

 

Call Eddie Spinks at American Air Suspension, he'll have everyting you need for your truck as well as the conversion parts, if you decide to go that way. Good to work with and he's a sponsor here.