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20V Vacuum Hose Routing

Posted: Fri Aug 04, 2017 10:57 am
by Tofu4u
Hello C4AG!

I may be beating a dead horse here but I've done some extensive research online and have piece-milled together whatever information I could find that makes sense. There is some contradicting information on the routes and a lot of forum threads are old with the pictures taken down. I feel this is a very important topic with swapping in a 20V and would be great to sticky and/or make this into a tech article. I need some assistance with identifying some routes with vacuum lines and the 20V. The motor is a ST with BT electronics.


- ST 20V with BT Electronics (MAP)
- Charcoal Canister will be used
- No A/C
- Power Steering will be used

I have numbered each point in the pictures below and wrote a brief description of what I think is supposed to be connected at that point. If you could help me verify what is correct and identify the points of question, I would really appreciate it!



1.) Throttle 1 – Vacuum Equalizer
2.) Throttle 2 – Vacuum Equalizer
3.) Throttle 3 – Vacuum Equalizer
4.) Throttle 4 – Vacuum Equalizer
5.) Fuel return line entrance (From Regulator)
6.) Fuel return line exit (To fuel tank)
7.) Central point exit for all 4 throttle vacuum equalizers (To MAP Sensor)
8.) Exit to MAP Sensor via 1 way valve
9.) Exit from Throttle Opener
10.) Exit to point 11 through manifold via 1 way valve.
11.) Where does this exit to?? VSV?
12.) Exit from VSV to Point 13 through manifold?
13.) Where does this exit to? Capped?
14.) Exit from VSV to Point 16 through manifold?
15.) Where does this enter from? Capped?

16.) Charcoal Canister
17.) ISCV Input
18.) What is this?
19.) Pressurized output to power steering idle-up valve (Not used)

Re: 20V Vacuum Hose Routing

Posted: Fri Aug 04, 2017 2:46 pm
by jondee86
My undertanding is that the four hoses marked 1, 2, 3 and 4 are from the spigots
under the ITB's that are used for the evap system. They exit under the edge of the
closed throttle plates and are not suitable as a vacuum source for a MAP sensor.

The ST uses a MAF so there is no dedicated MAP vacuum source. The best place to
tap for MAP sensor vacuum is any spigot that connects to the round cylinder that
sits at the end of the common vacuum rail. BT manifolds have channels for MAP
sensor vacuum sensing cast into the face of the intake manifold.

Cheers... jondee86

Re: 20V Vacuum Hose Routing

Posted: Sat Aug 05, 2017 6:07 am
by Tofu4u
Hi Jondee86.

Thanks for the quick reply.

I always thought that common port on the manifold rail would be a good spot to get an averaged vacuum signal as they all meet at 1 point.

You are saying a good point would be for example point 18? It taps directly into the common vacuum rail. I think this port was originally intended for AC idle up or something.

I found this thread earlier with your post and it helped a lot:

That line has a T junction with the fuel regulator and MAP sensor.

Btw, I'm trying to access that thread link from the old forum and it appears to be dead in the water :( ...the old forum was working a few days ago.

Are you able to shed some light on the other connections and the ones marked in red?

Thanks for your help.

Re: 20V Vacuum Hose Routing

Posted: Sat Aug 05, 2017 1:59 pm
by jondee86


Image ... _lines.htm

I don't have a 20V here to look at, and there are too many tubes/hoses in the
pics for me to guess which one goes where :) You already found the my-acoustic
pages which have a lot of good information, so you are halfway there :) The best
way to figure this out (if you have the hardware in front of you) is to look at what
is on the end of each tube/hose, and identify its function. Then sort the fuel lines
from the brake booster lines and vacuum hoses, and pin them down.

To get you started I would list down everything that you can think of that might
be located in the intake manifold area... for example...

- Brake booster (I think there are tappings off throttles 1 and 4)
- Fuel line in to rail
- Fuel line out from FPR
- vacuum line to FPR
- line from charcoal canister to evap solenoid
- hose from evap solenoid to evap throttle hard line
- hoses from evap hard line to throttles
- vacuum line to throttle opener
- etc
- etc

Each throttle is connected internally to the common vacuum rail, so that idle air
from the ISCV can make its way from the fat hose connecting to the round cylinder
into the engine. So any vacuum hose connected to the round cylinder will see an
averaged engine vacuum. But there will be a fair amount of pulsation, so when you
tap the vacuum rail for a MAP signal you need to make sure you use a pulsation
damper in the signal line.

Note that not everything you read on the internet is correct :o :o :o The vacuum
rail cannot supply "pressurised air" and no vacuum line will ever connect directly
to the inlet ducting. So you need to make allowances for language differences and
other people misunderstanding how things work.

Cheers... jondee86

PS: The old forums have been dead for a few months now, and it appears that they
have been abandoned. So unfortunately, what was the best 4AGE resource on the
internet has been lost :cry:

Re: 20V Vacuum Hose Routing

Posted: Sat Aug 05, 2017 6:35 pm
by Tofu4u
This is great information!

Yes, the my-accoustic page was super helpful. In regards to the misinformation I try to take whatever I find on the internet and take it with a grain of salt. It's comforting to find duplicate answers than ones that contradict.

I seem to have figured out the majority of connections and with your help the MAP routing makes a whole lot of sense now.

The last thing really is the VSV but now that the MAP is connected to the round cylinder, the rest of the plumbing can be figured out. I will take your advice on plotting out all the hardware one by one and double checking my work above.

Also, it's really unfortunate the old forums are long gone! I've been working on this project for about 4 years now and it's finally coming down to completion (mechanically). It's amazing the amount of information that was on there and how much it really helped every step of the way.

Well, I'll give this all a try and if something comes up I'll post it here!

Re: 20V Vacuum Hose Routing

Posted: Sat Aug 05, 2017 11:29 pm
by jondee86
This is for a BT but should be close to a ST setup....

Cheers... jondee86

Re: 20V Vacuum Hose Routing

Posted: Sun Aug 06, 2017 6:04 am
by Tofu4u
Brilliant! Also found this: ... index.html

It appears they are tapping into the #4 ITB vacuum line with a T to the throttle stop and MAP sensor. Not sure how well that worked out for them...

Re: 20V Vacuum Hose Routing

Posted: Sun Aug 06, 2017 2:39 pm
by jondee86
Tofu4u wrote:It appears they are tapping into the #4 ITB vacuum line with a T to the throttle
stop and MAP sensor. Not sure how well that worked out for them...

Should be OK. That is a legit vacuum tapping, but using only one throttle means
there will be a lot of pulsation. When I ran ITB's on a custom manifold, I tapped
all four inlet runners and averaged them with a small vacuum accumulator, then
took the MAP signal from that. Using the common vacuum rail seems to work
just fine for most people, and is a lot easier to set up :)

Cheers... jondee86

Re: 20V Vacuum Hose Routing

Posted: Mon Aug 07, 2017 7:37 am
by Tofu4u
I agree with tapping into the common vacuum rail as a more reliable source. It's just nice to have options when plumbing all this together from a troubleshooting point of view.

Speaking of pulsation, it's probably a good idea to add an in-line vacuum damper valve to the map sensor? This will keep the pressure reading more stable I suppose.

Re: 20V Vacuum Hose Routing

Posted: Mon Aug 07, 2017 2:59 pm
by jondee86
Yusss... you should always use a pulsation damper in the MAP line on an ITB engine.

Cheers... jondee86