working down my fix it list on the new-to-me 98 Mark...

Since day 1, the CHECK AIR SUSPENSION message comes on randomly, as quick as 100 feet out of the driveway, or up to 45 minutes into a drive. On some trips it never comes on, but more often than not it does.

When I've measured the corners it's always in spec from the measurements I've found in previous posts. The car does not settle overnight outside of specs. Pumped up with no message it is 26.75-27.75, and overnight it settled to 26-26.75. Frequently the light comes on after highway speed when you slow down and it should raise it to city speed.

I do NOT hear the vent when the door is shut after turning it off. I may have the first few days I had the car but I can't recall for sure. The 98, unlike the 94 has no visible door switches so I'm not sure what activates the vent.

I hear the compressor running on start up yet see no visible movement (I also tried the trick of resting my leg against the open door sill to feel it lift, no movement.) In these cases the light comes on after the compressor times out.

I wonder if one of the ride height sensors may be bad, the right front passenger one is turned backwards and wired to the control arm. A corner of the socket edge is broken off. The other possibility is, a weak compressor? Could it be running fine and sounding fine but not actually pumping much volume of air? I would think a bad vent valve would give the classic lifted rear end.


short of throwing a pricey part at it, is there any way to "test" the system to see what's triggering the light?

thx

** I see Eddies site but don't have a star tester, just wondering if there is any other way to test or if this means anything to anyone about what might be going on

formerly ASE certified, still skin my knuckles
98 Mark VIII Silver

Just a quick guess but it sounds like it's stuck at high speed height and the pump is too weak to pump it up higher but strong enough to not slam you.

To test it you need to adapt a pressure gauge to one of the little hoses going to any of the solenoids on an airbag, they all go to the dryer on the pump. Unplug the electrical connector to the solenoid or you may dump all the air out of it. Then turn on the ignition. It should give you some pretty high pressure, I'm not sure what the pressure should be but the new pump I have maxes out at 190 psi. You wont see the maximum because it will be trying to pump up the other corners.
My pump was going bad and it was taking longer and longer to pump the bags up until it was starting to set the light occasionally, so this sounds familiar.

ok, got a rebuilt unit from Eddie in 2 days (thanks Eddie!) dried out one of my spare driers, and swapped it out today. Lubricated the o-rings and got everything together and it pumped right up! And now when I close the door I hear the vent, so it must have been a weak pump. Thanks for the help! The bags are OEM Ford with no cracks so I think they may have been replaced at some time.

While was in there did the fuel filter and sanded down some rust and cleaned out the wheel well before the rust got out of hand, primed it all too.

formerly ASE certified, still skin my knuckles
98 Mark VIII Silver