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Old 09-01-2016, 12:29 PM   #1
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Vacuum Confusion -SOLVED

Vacuum issues got you confused ? Can't find details of routing? Bewildered by the crummy diagrams that show only part of the system ? Got at least 6 different print-outs and they are all slightly different?
Today is a great day to be alive on the 986 Forum - because most of your prayers have been answered but the answer is buried here:
See post # 17 for layout :Oh no, another...
video is here:
entire thread is here :
Oh no, another...
Kudos to the author and a challenge to anyone to improve on it !

Last edited by Gelbster; 09-01-2016 at 07:06 PM.
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Old 09-01-2016, 06:30 PM   #2
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Thanks Gelbster! I'll post some of it here to make it easier to find:

First, let me explain, there are a few separate systems that use vacuum from the intake. The most common one to fail is the secondary air injection system. That is the one I replaced. The other vacuum users are the brake booster and the fuel pressure regulator. Both of these looked good, so I left them alone. ***Tiptronics have a vacuum line that goes to a valve on the transmission. 2.7L and 3.2L engines have a vacuum line that goes to an actuator for the flapper valve on the front cross tube.***

This diagram shows the simplest system: 2.5L manual trans.

SAI vacuum system:
***This is for U.S. cars, the SAI was not used in R.O.W.***
The SAI is an emissions system that pumps fresh air into the exhaust for the first minute or two after a cold start. Common DTC codes when there is a vacuum leak in the system are p0410 and p1411. A failure of the SAI system will not damage your car, but a vacuum leak may cause the engine to run lean and lead to other problems.
-Remove the throttle body and cross tube for access to the rear part of the system.
-Remove the alternator for access to the front part of the system.
-Pull out all the old tubing.
-I replaced all the tubing, but reused the check valve and Y.
-Put it back in connecting to: 1) Electric change-over valve. 2) Vacuum source at cross-tube. 3) Vacuum resevoir. (2.5L 5 speed models have the simplest system)
***recommended: Also replace the small tube that connects the electric change-over valve to the vacuum powered change-over valve.
-Reassemble everything else that was taken out.


The video (Currently some sections of the forum allow videos to be embedded, some don't.):

Resonance flapper connection, 2.7L and 3.2L:

There are some other posts with good info scattered across the forums that we can collect and repost here:

-Brake boost vacuum line connects to right rear intake on the Tiptronics and the line includes a venturi.
-Brake boost vacuum line connects to the left front on the manual cars.
-Details about the flapper on the 2.7L and 3.2L.
Edit 5 Sept 2016: Added diagram showing resonance flapper connection.
I am not an attorney, mechanic, or member of the clergy. Following any advice given in my posts is done at your own peril.

Last edited by 78F350; 09-05-2016 at 07:10 PM. Reason: Adding more info
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