Hi, I am John Mc, a Lincoln dealer tech.
I hope I can help you quickly and accurately.

Unfortunately on these Navigators there isn't a whole lot you can do to diagnose them at home. This is why I believe it has taken so long for someone to chime in. This is one of the most complex suspension systems Ford has ever put in a vehicle. There are numerous items that can cause your issue, a bad compressor, a bad computer or even a leak in the system. The parts are easy to replace but once replaced the whole system has to be recalibrated by the dealers diagnostic system. I understand this is not what you wanted to hear... but it really is all I can tell you. The only other alternative without taking it to a dealer would be to install springs and shocks from an Expedition. More people then you would believe do this as it usually ends up being less expensive, has no future problems and to be honest rides just as nice, in my opinion.

In advance, Thanks for giving a positive rating! Ratings are how I receive credit for helping you today.

If you need further assistance for this problem before or after rating feel free to ask a follow up and I'll be
glad to help.

Thanks,
John Mc

If you need me and it says I am not in chat it is ok. I get a message as soon as you respond so I can come
right back.