Gents,

Just an exercise for us and learning together.
17th Nov evening I went out for dinner at CBD ( Central Business District ) area which I hate so much because it was peak hour and traffic jam is surely BAD.
I then observe my vacuum system pressure and I notice something is not right. I can't achive a near zero pressure which means near maximum vacuum when brakes are not being used.

The sensor I use is an Absolute one, which means at ambient pressure at sea level, it will read 14.5psi there about ,if engine is OFF and vacuum system exhausted or not yet primed.
When vacuum pump starts working, it will read close to zero PSI, meaning near 30 inHg.
When ever I depress the brake, the vacuum will decrease or be at approx 5 PSI absolute.
And in my turbo M276, the turbo actuator also uses the vacuum pump but very little is used.
So when I do not depress the brake, the vacuum system will recover and be near zero PSI again.


This is the log, TO and FROM the CBD area.



While in the car crawling in the traffic while going TO the CBD, I already start noticing why the pressure keep hanging at 5 PSI and not down to near zero when I do not use the brake.
The log above is so obvious something is wrong.
At every engine start, I will wait at least 30 seconds idle before moving, this is with warm engine, which is FROM CBD.
TO CBD log is from cold start and that means 120 seconds I will let car idle at least and vacuum pressure at 4 PSI absolute is a confirmation there is a problem.

So I back track my older log.

Yesterday 16th Nov when I was spinning my rear wheel to hear the parking brake pad "kissing/touching" the rotor drum.

Above is already trouble in progress. Data point 401 to 841 is brake not being depressed and that is 440 data point at 5hz = 88 seconds and my vacuum should achieve near zero PSI, by right.



Last Sunday, 13th Nov. To my friend's private marina.

Above is normal, the vacuum system can achieve zero PSI when brake pedal not depressed.


====================

I have not inspected the vacuum system yet.
Now let's have fun together and make a guess which is the culprit.
I will explain the system first.

Vacuum pump only serves 2 devices in my car. 1 big hose to brake booster.
1 small hose for turbo vacuum actuator which has a Y splitter to share to Bank1 and Bank2 turbo's wastegate, via the turbo boost controller solenoid.

Basically the possibilities are :
AA. The vacuum pump itself not able to pull deep vacuum due to internal leak.
BB. Leaking big hose from vacuum pump to brake booster. 2 hoses actually.
CC. Leaking small hoses from vacuum pump to turbo related vacuum operated wastegate system
DD. Leaking at brake booster housing.
EE. My BanksPower vacuum sensor goes banana giving me wrong vacuum value or its siicone hose is indeed leaking.

So gents, let's make the bet.......
Tomorrow me will start digging..........

 

My bet goes to something to do with the brake booster or its vacuum check valve.

Knowing how the advanced German EPD and plastic are formulated planet-friendly to fall apart like chewing gum... I would not be surprised if you found a bad check valve rather than bad booster diaphragm:

• requires specialty troubleshooting
• easy part to replace
• perfect MB maintenance item
• gradually degrades performance

I may follow your lead and work on my booster. It has been leaky first month after new. My booster gets aired out: hard to depress brake pedal to crank this car.
✌️

 

And the result is ...................... Banks-Gauge The BAD dude !!
Below is based on assumption that the analog capillary gauge on my MityVac vacuum hand-pump assumed as 100% accurate.



Damn.... such a short lived reliability.
I did not scope the pressure sensor voltage output, as I do not have its voltage table.

At the least I got to test all hoses, at least it has benefit too.


===============

01A. Vacuum pump small hose to turbo boost controller - OK




01B. Small hoses of : Turbo boost controller to both wastegate vacuum actuators - OK




02A. Big hose of vacuum pump to intermediate bulkhead joint at heat shield firewall. - OK







02B. Complete : big hose, the bulkhead intermediate joint which is actually another big hose and finally to brake booster - OK

ABOVE : My hand pump can't do better than 20 inHg if for up to brake booster vacuuming, too tough a duty...LOL.
At least no vacuum decay, so no leak.



03. Check valve at vacuum pump - OK. Oral test




04. Banks Power, absolute sensor test - The Bad Dude
I even use electric vacuum pump to get deepest vacuum.




Reading should be near zero PSIA , by right.



My electric vacuum pump is not 100% healthy. It can only do 2,250 micron at on pump suction port. If super healthy and dry new oil, 400 micron is possible.






Micron in relation to other commonly used vacuum units of measure





At least this is a low cost issue. US$72 damage, FOB USA.
https://bankspower.com/products/sens...41225176547525

Good thing the error ONLY starts at 20 in-Hg and deeper vacuum, so I am not totally lost.
I mean the data is still useable as early warning.

 

U mean your new booster is leaky ?

Under ESP, I believe ESP module, the scanner can access the pressure/vacuum sensor built in at the brake booster.
So you can once in a while do a check with engine ON to see if deep vacuum is available from vacuum pump.