Mountaineer RWD V6-4.0L (2008)
Vacuum Brake Booster: Testing and Inspection
Brake Booster
1. Disconnect the check valve from the brake booster.
2. Apply the parking brake, start the engine and place the transmission in NEUTRAL.
3. Verify that manifold vacuum is available at the check valve with the engine at idle speed and the transmission in NEUTRAL.
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If manifold vacuum is available, stop the engine, connect the check valve and continue with Step 5.
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If manifold vacuum is not available, continue with Step 4.
4. Disconnect the check valve from the vacuum hose and verify that manifold vacuum is available at the hose with the engine at idle speed and the
transmission in NEUTRAL.
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If manifold vacuum is available, stop the engine, install a new check valve and continue with Step 5.
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If manifold vacuum is not available, stop the engine, connect the vacuum hose to the check valve and diagnose the no vacuum condition.
5. Apply the brake pedal several times to exhaust all vacuum from the system.
6. Apply the brake pedal and hold it in the applied position. Start the engine and verify that the brake pedal moves downward after the engine starts.
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If the brake pedal moves, the brake booster is operating correctly.
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If the brake pedal does not move, install a new brake booster.
7. 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 brake booster check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air.
