Tube blocked off on top of manifold?
 

Hi All,

I noticed that my automatic 2015 BRZ does not have a tube connected to the manifold next to the tube that connects to the PCV valve.

What is this tube (drivers side) for? Mishimoto catch can install says that's the brake booster tube but I don't think so. Radium video says that the crankcase vent. I think this is correct.

If there's no tube because mine is an automatic, why don't I have a crankcase vent? The port is just blocked off straight from the factory. Last time I checked, I do have a crankcase. :)

Vic

PS. Google search was no help. I couldn't find a single photo of this area with the port blocked off like it is on my car. 1st owner so I know it came like this from the factory.

There's already an EXACT post about this.

I've been trying to find this info using search here for the past hour.

"blocked port, tube next to pvc port, plugged port, mystery port, plugged connector on top of manifold etc..... NOTHING"

Kindly point me in right direction.

I believe that's plugged from the factory. Probably another vacuum port for diagnostics

Manual uses that for brake booster. Auto uses something else so it does not need/use it.

Because auto doesn't go fast enough for boosted brakes?

Is that sarcasm? Hard to tell just from reading.

That is sarcasm.

This is not sarcasm.

Auto uses a separate pump.

Why? Is there a reason for this? I've been looking for days and can't find a definitive answer. The AT and MT version both have the same Brake Booster part number, but one gets vacuum from the intake Manifold (MT), and the other gets vacuum from the Cam-driven Vacuum Pump on the rear, passenger side of the engine (Where the leaky cam plate is on the MT version). But why?

What's stopping me from just using the plugged port on the intake manifold for brake booster vacuum? If nothing, then why have the pump at all?

No idea. If the engineers that designed the engine felt that was a good reason for the two different systems I have to believe them. Each little difference adds cost and they don't add cost unless they have to.

Might be for reading vacuum?

I've never looked at the PCV diagram for a CVT, but I would bet $1 it's because an auto does not pull nearly as much manifold vacuum when you let off the throttle. So an external vacuum source is required.

If you transition from throttle to brake in a manual, you get a lot of manifold vacuum. In an auto, you take your foot of the throttle it upshifts (and some CVTs go to idle) and you have little-to-no vacuum.