Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMERCURY1989GRAND MARQUIS GSREPAIR AND DIAGNOSIS (SINGLE PAGE)SUSPENSIONREAR SUSPENSIONSUSPENSION - REAR LEVEL CONTROL SYSTEMTESTINGLEAK CHECK
1989 Mercury Grand Marquis GS
Leak Check
1989 Mercury Grand Marquis GSSECTION Leak Check
NOTE:
If compressor is run to maximum pressure the vent solenoid valve will function as a relief valve. The leak-down, after compressor shut-down will indicate a false air leak.
- Repeat steps 1) and 2) of RESIDUAL PRESSURE CHECK. Allow the system to fill until the gauge reads 70-100 psi (483-690 kPa). With load still applied, disconnect wiring harness connector from the microcomputer module and then remove the load.
- Rear of vehicle should rise. Turn ignition on then off. Observe system for leaks for about 15 minutes. If system will not inflate to more than 50 psi (339 kPa), a severe air leak is indicated. Check air line between compressor and shocks for damage.
- Check all connections with soap/water solution. If pressure is stable, perform diagnostic test.
- Attach wire connector to module. Turn ignition switch from "OFF" to "RUN" position. Allow air to exhaust and vehicle to lower. Remove pressure gauge from system and reconnect drier. Turn ignition from "OFF" to "ON" and repeat step 2) of RESIDUAL PRESSURE CHECK. Perform SYSTEM OPERATION CHECK.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.