Crown Victoria V8-281 4.6L SFI (1998)
Vacuum Brake Booster: Component Tests and General Diagnostics
1. Check the hydraulic brake system for leaks or insufficient fluid.
2. With the transmission in PARK, stop the engine. Apply the brake pedal several times to exhaust all vacuum in the system.
3. With the engine turned off and all vacuum in the system exhausted, depress the brake pedal and hold it in the applied position. Start the engine. If
the vacuum system is operating, the brake pedal will move downward under constant foot pressure. If no motion is felt, the vacuum power brake
booster system is not functioning.
4. Remove the vacuum hose from the power brake booster check valve. Manifold vacuum should be available at the check valve end of the hose with
the engine at idle speed and the transmission in NEUTRAL. Make sure all unused vacuum outlets are properly capped, hose connectors are
properly secured and vacuum hoses are in good condition.
When it is established that manifold vacuum is available to the power brake booster, connect the vacuum hose to the power brake booster and
repeat Step 3. If no downward movement of the brake pedal is felt, replace the power brake booster.
5. 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 lbs.) of force. The pedal feel (brake application) should be the same as that noted with the engine operating. If the brake
pedal feels hard (no power assist), replace the check valve, then repeat the test. If the brake pedal still feels hard, replace the power brake booster.
If the brake pedal movement feels spongy, bleed the hydraulic system to remove air from the system.
