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BRAKE BOOSTER internal + 2 hoses + the big check valve at the vacuum pump. Basically this is what the test covers.
The brake booster spring is tough, the hand vacuum pump pistol can't do better than 12 inch Hg VACUUM aka negative pressure.
I am too lazy to rig a vacuum system to my 8CFM vacuum pump to replace the hand pistol version.
Anyhow, we need only to see if the vacuum decay is acceptable or not.
A 2 inch Hg Vacuum decay in 8 minute is acceptable. Most likely this minor vacuum leak is at the brake booster and not the big check valve at vacuum pump.
Honestly I do not yet know the baseline if say a brand new W212, what slower vacuum decay is to be expected ?
Even my vacuum pistol, its check valve is not say very tight....
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Those with turbochargers and with the turbo boost or wastegate controller solenoid or having other vacuum powered actuators like M272 intake flap...or similar.
Two kind of test. The diagram will show you Test A or Test B test which components + hoses.
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TEST A is a method to test the small check valve and the supporting mini hoses, without needing to remove the small check valve at the vacuum pump.
If that small check valve membrane is gone, torn or whatever, you wont be able to vacuum down this Test A even for a mere 5 seconds.
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Okey, go and get MityVac vacuum pistol or similar and do this test once in a while.
Thank you Surya for dealing with W212 vacuum booster decay.
I have been surprised before by a stiff brake pedal trying to start the car.
There are couple issues that can impact the performance of our vacuum services. Three check valves are used to preserve vacuums separately.
The pump two outlets each have a valve in contact with hot engine oil.
> Popular Issues Are:
Brake booster has poor performance
Pump small check valve is blown up
Vacuum line contaminated by oil
Vacuum pump is filled up with oil
> Brake Vacuum Booster:
This service holds the top priority. Expectations are a mixed bag because the nature of vacuum issues are poor performance, not binary.
You don't want to to go to a dealer to complain about "poor braking power". Everything A to Z will get replaced except 99% chance the root-cause will be left untouched.
The brake booster stores vacuum with the help of a dedicated reliable check valve. The computer (ECU/ESP) has a vacuum sensor to track booster vacuum.
If booster offers poor performance the issue is actually caused by the pump being affected by high crankcase pressure caused by piston rings blow-by pressure.
pump serviceable check-valve
On the maintenance list, the pump tiny check valve is a good item to keep an eye on.
It's a collateral damage of pump seeing high pressure engine oil. It's hard to tell how long new check valve can last under unfavorable conditions.
The bottom line with the vacuum pump is you need decently low crankcase pressure else braking power is directly affected.
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Last edited by CaliBenzDriver; Dec 9, 2023 at 04:01 PM.
I have always wanted to install a crankcase pressure sensor, but Banks Power does not sell such low value high resolution pressure/vacuum sensors.
I need to get one capable of -0.3 to +0.3 PSI. But too bad Banks Gauge is either BAR or PSI in a 0.00 decimal point which is not low enough for typical crankcase pressure , better 0.000 tripple digit after zero.
There is a facility on my Banks gauge for custom sensor, but need to program it and find the suitable 5V sensor first.
Also space wise I need to then place my Banks Module separately.
Now 3 Banks Module is maximum already and soon a 4th module is coming, the 4 channel thermocouple one.
That brown cable is an Omega thermocouple wire is on stand-by. That is stick-ded to the EVAP's TXV so that I can read evap temperature and later HVAC compressor temperature at output port and
the condenser output temperature. So 3 channels will be used, I then got 1 spare channel.
I forgot , I must also buy 2 of these extension wires so that the extra Banks Module can be relocated near the main battery at LEFT side of car, for a RHD car. https://bankspower.com/products/sens...41239485907141
The only other cooler location of engine bay is on the left of the battery.
Down there actually has some decent real-estate if only 2 of Banks Module.
Let me brainstorm some more for crankcase pressure sensor.
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, I must also buy 2 of these extension wires so that the extra Banks Module can be relocated near the main battery at LEFT side of car, for a RHD car.
