The Car Was Puffed Up on Hot Air

I had a Lincoln Town Car come to me for repair that required some real detective work to figure out what was wrong. The issue wasn't actually electrical in nature -- my expertise. It turned out to be a clogged filter and faulty logic in the ride height computer control. Let me explain.

It was a mid-80s Town Car with the air bag suspension. When the car was started and driven for a while, the suspension would go to its full travel height, similar to when all the kids were putting "Hijacker" air shocks on their cars. This made the car very unstable at highway speeds (not to mention it looked ridiculous).

If the car sat overnight, it would be level in the morning. By the time the car was brought to me for repair, the air bags, ride height control module, ride height sensor, etc. had all been swapped out, and now the customer was running out of patience (and money). I tested the wiring, the control solenoids, the height sensor, and the pump. All checked out electrically.

Eventually, I put a test light across the vent solenoid to verify when it was being activated. Apparently, the control computer would attempt to vent the air bags until the height sensor said the car was level. If a certain amount of time elapsed while venting without the car lowering to level, the computer would assume the height sensor was bad, and that the car was sitting on its suspension stops.

The computer would then inflate the air bags for a pre-programmed amount of time. Once this cycle was repeated a couple of times, the car would be at full travel. It turned out to be a clogged filter in the pump housing assembly that allowed the air out of the system. I popped the filter out, and pfffftttttt, the car went to level and stayed there, even when driven.

This entry was submitted by George Tempesta and edited by Rob Spiegel.

George Tempesta is a former automotive electrician who is currently a network engineer/architect with an IT consulting services company based in Philadelphia. He spends most of his time trying to figure out how things work, fixing things, or building something.

Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.

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