Grand Marquis V8-4.6L VIN V Flex Fuel (2006)
Vacuum Brake Booster: Testing and Inspection
Brake Booster
1. Check the hydraulic brake system for leaks or insufficient fluid.
2. With the transmission in NEUTRAL, stop the engine and apply the parking brake control. Apply the brake pedal several times to exhaust all
vacuum in the system.
3. Apply the brake pedal and hold it in the applied position. Start the engine. If the vacuum system is operating, the brake pedal will tend to move
downward under constant foot pressure. If no motion is felt, the power brake booster system is not functioning. Continue with these steps.
4. Remove the vacuum booster hose from the check valve connection. Manifold vacuum must be available at the check valve end of the vacuum
booster hose with the engine at idle speed and the transmission in NEUTRAL. If the manifold vacuum is available to the power brake booster,
connect the vacuum booster hose to the power brake booster check valve and repeat Steps 2 and 3.
5. If no downward movement of the brake pedal is felt, install a new power brake booster.
6. Operate the engine a minimum of 10 seconds at fast idle. Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal
with approximately 89 N (20 lb) of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels
hard (no power assist), install a new power brake booster check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to
remove air. For additional information, refer to Brake System Bleeding.
