[TurboVanAK]

I have a 89 2.5 Turbo Caravan and I am rebuilding the top end. I am also removing the emissions gear.

My confusion is with the vacuum lines. I see that some people run the large nipple on the Intake Manifold to an vacuum block and then patch those in to the MAP, The, Barometer, The FPR, The WGS, etc...

If the intake is normally a vacuum, then when it is boosted does it not become pressurized?

### Ignore this, found the answer###
Also is there an advantage of running a vacuum line from
Intake > Barometer Sensor > Map Sensor.

Rather then
Intake > Barometer > Capped
Intake > Map Sensor
### Ignore this, found the answer###

Thanks

 

[TurboVanAK]

Found one part on what I needed to know regarding the MAP to the Barometer... I had searched for it earlier, but just found it.

Technically 4, here is the minimum

From intake -

- BARO Solenoid - MAP Sensor
- Wastegate Solenoid/MBC - Wastegate
- EVAP Solenoid - Evap Canister - TB
- Fuel Pressure Regulator

If Equipped -

- EGR Solenoid - EGR
- Boost Gauge

(most all intakes take vacuum pressure from the back to send to the brake booster, so this line is omitted)

Also, regardless of what MAP sensor you have, IT HAS to be hooked up to the solenoid. The Solenoid opens and closes constantly on a turbo car, which measures Barometric Pressure (for those who do not know, ambient air pressure) and adjusts fuel accordingly, so you do not destroy your car in lower elevations, or it turn into a turd at higher elevations.

TBI and normal FI cars only check BARO pressure once, before startup. This is why if you drove a car from the bottom of a mountain to the top, there would be a drastic difference in performance as your car rose in elevation. This is why they suggest shutting off your car every once in a while while traveling through mountains/high elevation changes.

With regards to the Vacuum/Boost that the intake sees, how does this effect the brake booster?

 

[NAJ]

Welcome To TD.


The brake booster uses a one way check valve that allows vacuum to enter but not pressure and also keeps vacuum stored in the booster.
As soon as you release the throttle you are back in vacuum so brakes will work normally.

I would be happy to explain other component/system operation if you need/want more info.

Just incase....
The Map Sensor needs to see boost so the controller can change the fuel/advance curves accordingly to compensate for changes in engine load.
The vacuum line needs to run to the Baro Solenoid and from the Baro to MAP.
The controller uses the Baro Solenoid to stop and bleed vacuum to the Map so it can update Barometric Pressure readings on the turbo cars.
One port on the Baro Solenoid is a vent and remains open.
Boost needs to be present at the Fuel Pressure Regulator or rail pressure will not increase with boost.
Boost also needs to be present for your boost gauge.

 

[TurboVanAK]

Thanks for the Welcome as well as the reply.

Ok, that makes sence. You would not need power assist brakes at boost, as soon as you let off the gas, you would have a vacuum, then you have power brakes.

Now on the TB, you have two nipples. Are they both the same, as in they see both vacuum and pressure? The chilton shows the left one i beleive as ported which I think is vacuum only. I could be 100% wrong.

Are there any dedicated Vacuum only ports?

 

[EvilcowRoland]

You're still slightly off. As NAJ pointed out, the brake booster should ALWAYS see vacuum when the engine is running. There is a one-way check valve between the intake manifold and the booster. It draws air out under vacuum and does nothing under boost, but the vacuum already generated remains in the booster.

This incidentally is the answer to your other question. There are no dedicated vacuum-only ports on a turbo car. However, you can use a one-way check valve to create a vacuum-only system. There should be 4 items on your van that need vacuum only: Brake booster, cruise control (if you have it), HVAC control, and the emissions equipment.

The 2 ports on top of the throttle body both see boost pressure but they are different. One of them opens up behind the throttle blade and the other opens before it. The one behind the blade will see vacuum when the throttle is closed whereas the one in front will simple drop to 0 when the throttle is closed. Both ports see boost when the throttle is open.

 

[TurboVanAK]

That clears everything up, Thank you to both of you.

 

[NAJ]

Anytime you want/need info feel free to ask.