[rcoe]

Originally Posted by ctrlz

My batting percentage has not been too high with this thread, but anyway...
I think one side of that T draws vacuum from the intake manifold. The part that runs up by the headlight goes to the electric vacuum pump, which is mounted next to the radiator. This ensures the brake booster always has vacuum. I would expect a check valve somewhere on that line to the intake to protect the brake booster from boosted induction pressure.

You are correct one end of the line goes to the back of the intake manifold the other should end at the vacuum booster pump. I cannot see the pump without removing the bumper. There is a check valve in the line coming from the manifold.

Not sure how the pump is plumbed or how it operates. Maybe the pump closes where it is venting to open air when the car is running or key on.

[ctrlz]

Originally Posted by rcoe

Not sure how the pump is plumbed or how it operates. Maybe the pump closes where it is venting to open air when the car is running or key on.

I don't think it vents.
This is what i found:

DIAGNOSTIC INFORMATION AND PROCEDURES > DTC C027B: BRAKE BOOSTER ELECTRIC VACUUM PUMP > CIRCUIT/SYSTEM DESCRIPTION
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic
brake control module supplies a 5 V reference and a low reference circuit to the brake booster vacuum
sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to
the electronic brake control module. When the vacuum within the system becomes weak, the electronic
brake control module turns ON the brake booster pump motor by providing ground to the brake booster
pump motor relay. The relay activates and supplies battery voltage to the brake booster pump motor.

DESCRIPTION AND OPERATION > BRAKE BOOSTER VACUUM ASSIST
DESCRIPTION AND OPERATION > SYSTEM OPERATION
The pump can be switched on and off by the Electronic Brake Control Module based on the required
vacuum. Pressure variations during braking can be measured, and the pump can be activated to
generate additional vacuum if required to increase the braking force.
The pump runs for the first 5 seconds after engine running to perform a self test. Engine running, the
pump may run another 30 seconds and then turns off, due to the timer relay. The pump has a maximum
run time of 180 seconds per ignition cycle with engine running, when it reaches the maximum run time
the pump shuts down to cool off and will not allow the pump to run again until the next engine run cycle.

[JSH]

When I saw "educate me on vacuum", I said oh god we'll need an automobile design class to cover vacuum and all of its different functions