Vacuum booster - loses power brake assist overnight?

[metroplex]

I've noticed my 2014 SHO has had an issue where if I don't drive the car for maybe 1-2 days, the brake booster loses vacuum. I can store my Mustang GT for a whole year and there would still be vacuum inside the brake booster.

Is this normal for the SHO? This problem has existed since the car was new.

[SHOdded]

Sure sounds like a check valve/ brake booster issue.

Brake Booster

1. Disconnect the brake booster vacuum sensor/check valve from the brake booster and connect a suitable vacuum/pressure tester to the booster side of the vacuum sensor/check valve.

2. Apply the parking brake, start the engine and place the transmission in NEUTRAL.
  - Allow the engine to reach normal operating temperature.

3. NOTE: Subtract approximately 3.38 kPa (1 in-Hg) from the specified reading for every 304.8 m (1,000 ft) of elevation above sea level.

Verify that vacuum is available at the vacuum sensor/check valve with engine running at normal idle speed.
  - The vacuum gauge should read between 51-74 kPa (15-22 in-Hg).
  - If specified vacuum is available, stop the engine, connect the vacuum sensor/check valve and continue with Step 5.
  - If specified vacuum is not available, continue with Step 4.

4. Disconnect the vacuum sensor/check valve from the vacuum hose and verify that the specified vacuum is available at the hose with the engine at idle speed and the transmission in NEUTRAL.
  - If specified vacuum is available, stop the engine, install a new vacuum sensor/check valve and continue with Step 5.
  - If specified vacuum is not available, stop the engine, connect the vacuum hose to the vacuum sensor/check valve and refer to Section 303-00 to diagnose the no/low vacuum condition.
  - On vehicles equipped with a brake vacuum pump, if specified vacuum is not available, inspect the vacuum hose and install new as necessary. If vacuum hose is OK, install a new brake vacuum pump. Refer to Section 206-07 .

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.
  - If the brake pedal moves, the brake booster is operating correctly.
  - If the brake pedal does not move, install a new brake booster. Refer to Section 206-07 .

7.Operate the engine a minimum of 20 seconds at idle. Stop the engine and let the vehicle stand for 10 minutes, then apply the brake pedal. 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 vacuum sensor/check valve and retest.
  - If condition still exists, install a new brake booster. Refer to Section 206-07 .
  - If the brake pedal feels the same as noted with the engine operating, the vacuum sensor/check valve is functioning properly.

[ZSHO]

I certainly agree with SHOdded and its most likely a bad,leaking check valve,any excessive hissing sound coming from the brake reservoir area??Do you have Torque pro to monitor/check vacuum level in drive? Z

[metroplex]

I don't hear any hissing and the vacuum is about 18.7 inHg.

[ZSHO]

I don't hear any hissing and the vacuum is about 18.7 inHg.

I would Not DRIVE IT!!,Any mods to the vacuum line?  Z

[SHOdded]

Did you check with the engine idling or with it off, metroplex?  If off, how long as it been off?

[metroplex]

Engine running (idling) in drive, with the engine fully warmed up.

[ZSHO]

Did you check for any codes stored.?  Z

[metroplex]

No DTC's.

[SHOdded]

Complete the rest of the diagnostic I posted above to confirm the issue.

[metroplex]

It has to be a somewhat slow leak, because all of the steps show the brake booster is fine.

[metroplex]

I pulled the check valve and it isn't really a check valve, just an elbow fitting. I read the F150s with ecoboost engines use a vacuum pump (either electric or belt driven).

Is everyone else's EcoBoost SHO able to keep vacuum in their booster for over a day without driving the car?