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Danglerb 07-23-2008 11:26 PM

OB vacuum lines
I've been looking at the vacuum control system and lines, studying the diagrams, and SLOWLY putting all the vacuum and breather lines back on my US 83 after a pull off stuff and clean etc. of the throttle valley. I think I mostly have it sorted out as to what goes where, but I am still scratching around at routing the lines. Below are my notes and some pictures.

Airflow and vacuum lines on a US 1983 5 spd (AT has a line to transmission for shifting point).

The flow of air is through the filter, down the air meter, into the U, up through the throttle, into the plenum, and down the intake legs to each cylinder. The closer to the cylinder generally the higher the vacuum, and the closer to the air filter the lower the vacuum.

This is the throttle body (throttle open)

Big screw on the right of picture is the idle control, and it adjusts how much air bypasses the throttle plate through the two holes on the right inside of the throttle.

Closer view of the inside.

Big tubes on the left side go to the vacuum limiter, and allow a moderate flow of air to bypass the throttle plate at very high vacuum levels (otherwise at high rpm with the throttle plate closed "foot off the gas" too little air would get to the cylinders for the fuel to burn properly). (more later)

Look carefully and you should be able to see a small hole above the shiny flat ridge, and an even smaller hole just below the darker area. These holes are connected to the two rear vacuum ports on the throttle body.

The larger one is called manifold vacuum and feeds all the controls that need to track engine load as seen by each cylinder as well as the state of the throttle plate.

The smaller one is just barely below the position of the throttle plate when closed, and I think is called "ported" vacuum. At idle with the throttle closed, there is little if any vacuum (same as in the U basically), but just a tiny amount above idle and the vacuum increases to full manifold vacuum. It feeds all the controls that switch between idle, cruise, and WOT (wide open throttle where manifold vacuum is fairly small). Cruise is when a lot of smog control stuff goes on, like EGR.

Danglerb 07-24-2008 12:11 AM

Another picture of the rear ports.

Holes from the front ports are REALLY hard to see, but they are there and both are on the manifold side of the throttle plate. I'm not sure if they provide a different vacuum signal than the rear port that is also above the throttle plate, but as the throttle plate opens the edge passes over these holes, so it may be "funny".

This is the U tube, throttle goes on one end, and air meter goes in the other.

Closer view shows how the external tubes feed directly into the main body of the U.

Danglerb 07-24-2008 12:52 AM

Vacuum for the brakes and climate controls comes from this funny looking Y shaped thing. Its a venturi tube, with filtered and metered air from the U going through it directly to the manifold plenum and internally flowing over a venturi which creates a strong and very reliable source of vacuum that stays fairly constant as long as the motor is running.

Vacuum tubes goes through the firewall. White tube goes to the heater/coolant valve, and black hose goes I think to the ignition brain.

This is my current mess at the brake booster, and may have more than one thing wrong with it. Clear line going into the fender is I think for the vacuum storage tank.

Danglerb 07-24-2008 12:55 AM

This is a top view from the front of my throttle body and connections to it.

I used a T directly on the throttle body Ported Vacuum (3 in the WSM 24-14 diagram), one leg goes to the thermal switch at the rear of the passenger side of the valley, and the other leg goes to the distributor vacuum advance.

So many things coming off the Mainfold Vacuum I start with a 4 way instead of a T.

Front to back, canister valves, vacuum flow limiter and basic on/off, farther back the air pump diverter valve.

Another view.

Danglerb 07-24-2008 12:59 AM

This post is a space holder for routing.

Danglerb 07-24-2008 12:59 AM

one last space holder.

surfdog4 07-24-2008 03:40 AM

if you figure out the routing it would be fantastic if you posted a diagram or listing. My '81 was/is a mess with the vacuum lines, the series of PO's have done all sorts of things, and the diagram in the manual is vague at best.

For example, those two ports on the back of the throttle, it had one connected to two hoses through a "T" and one (the lower one) completely disconnected. Well not knowing better i disconnected the "T" and put one hose on one port and one on the runs a lot better now (probably because i closed a big leak) but i cant tell from the diagram which hose goes to which port on the throttle.
(the diagram seems to show that the hoses should be different colors but mine were all the same).

A better connection diagram would be a real "yahoo" for me.


surfdog4 07-24-2008 03:54 AM

going back to the manual just know i discovered page 24-14 with a photo of where 3 of the throttle vacuum lines go tucked in the prodedure for removing throttle body (not a fan of these electronic manuals..i don't do as much "browsing")..yipee!

Danglerb 07-24-2008 08:45 AM

Routing will come asap, but for now the important thing is that the two ports on the rear are DIFFERENT, driver side is manifold vacuum and goes to things like the fuel pressure regulators, vacuum limiter etc., and passenger side is "cruise" "off idle" vacuum and goes I'm not 100% sure where (tonight I should know) smog stuff I think. The ports on the front, may be the same manifold vacuum, or possibly slightly modified due to the proximity of the edge of the throttle plate as it opens.

Manual page 24-14 is great.
Front port; distributor (retard)
Rear driver side; deacceleration valve (vacuum limiter), fuel pressure stuff.
Rear pass side; distributor (advance) (ignition brain I think), vacuum check valve (charcoal canister) (there are two valves, not sure which).

TBD (to be determined)
Thermal valve routing
Air pump diverter valve.
Canister valves.
Where exactly the distributor advance hose goes.
Physical routing path of the vacuum lines, where tie wraps go etc.

surfdog4 07-24-2008 05:00 PM

well armed with my new knowledge i came home, took off the air box, and started checking the hoses..

first, the rear ports were reversed, found out that the hose to the temperature switch was completely disconnected

basically all the hoses to the carbon canister were rotten and disconnected

of course i replaced all the small lines, reversed the back throttle hoses and viola! runs like crap!

so i'm guessing either the temp switch or purge valve to the canister has a leak that i have now put "in the loop" guess i have to go back and do a little more testing.

On rennlist someone had a listing that had the rear throttle ports opposite from the manual..which is the way mine were hooked up..i thought it was a typo but now i wonder.. i might also have the connections to the thermal switch backwards

ROG100 07-24-2008 05:28 PM

You come up with a shematic and I will come up with a kit.
Thanks for your efforts.

Danglerb 07-24-2008 08:44 PM

Couple of points aren't too clear to me, are there two kinds of distributor, vacuum advance and vacuum retard? and can't remember the other one.

On my distributor using the mighty vac, vacuum increasing rotated the assembly counter clockwise. If I got it right, thats vacuum advance, which means control has to be from ported vacuum.

N2O-SHARK 07-26-2008 09:11 AM

Not sure if this will help you.

It's for KIS but the TB hook ups should be the same.

Danglerb 07-26-2008 11:46 AM

Its close, but still different. Monday I will hopefully remember to take a picture of the sticker under my hood. This is what I have done so far, routing still a bit tbd.

1) Front port, manifold vacuum at idle, part throttle goes to U tube pressure, line to the side to rear canister valve. Hose between the two canister valves is $75, so I have a cobbled together 5/16 hose stuck inside a 1/2" hose and I think I should have made it longer to put the valve between the overflow tank and filler neck for the windshield washer.

2) rear port, constant manifold vacuum.
90 degree elbow, short section to inside of passenger intake "kink", 4 way splitter, line to front fuel thing, line to canister flow limiter (forward canister valve), very short line to T, line to throttle vacuum limiter, line to T at the rear of passenger side, short line to passenger side fuel thing, longer line to driver side fuel thing. Vacuum limiter could easily enough have the T on it directly.

3) rear port, ported vacuum, U tube at idle, manifold at off idle, T directly on port, line forward to distributor advance, line back to thermal switch, from thermal switch through 3, 4 intake tube space to air pump diverter valve.

If that seems "reasonable" Monday or Tuesday I will try to measure everything.

surfdog4 07-28-2008 04:22 AM

I've got a diagram that shows the vacuum line going from port "3" (passenger side) on the throttle body to the temperature valve and from the temperature valve to the carbon cannister "valve" (one place called it a "purge" valve and one called it a check valve.

Part of my confusion is all the different diagrams and the multiple names for the various parts (Decel valve = Vacuum control)

Danglerb 07-31-2008 09:39 PM


Originally Posted by surfdog4 (Post 4086138)
I've got a diagram that shows the vacuum line going from port "3" (passenger side) on the throttle body to the temperature valve and from the temperature valve to the carbon cannister "valve" (one place called it a "purge" valve and one called it a check valve.

Part of my confusion is all the different diagrams and the multiple names for the various parts (Decel valve = Vacuum control)

3 is the ported vacuum, and I have it to a T once side to the distributor, and the other to the temp switch and then to the canister vent "on/off" valve.

*** T is connected directly to vacuum limiter.

Sorry, buttoned up today instead of measuring. I wasn't feeling 100% on the exact routing, where it connects I am almost certain is correct, just not that I have the lines running in the best or factory locations. Here are a few more picts.

Getting that last clamp tightened down on the spider was very nice.

I rerouted the breather line between the canister vent valve and the flow limiter so the vent valve was farther back where I think it is supposed to be.

Showing the routing a bit more.

surfdog4 08-01-2008 07:36 AM

did you find metric hose for the carbon canister hoses or are english unit ones OK?

Danglerb 08-01-2008 09:15 AM

The hose between the canister shut off and the canister flow limit valves is supposed to be a Porsche 928.110.652.02 Hose (2 recommended) $72.03, and I used Gates 5/16 stuck into Gates 1/2" both purchased at NAPA for $1 or so each a ft. Fit on the connectors was tight, a total sob to remove, but goes right on with a shot of silicone spray. My hose through the fender to the canister itself looked fine, so I did not replace it.

For the breather lines seeing manifold vacuum I used the $35/M Porsche VRT DOT approved hose.

surfdog4 08-01-2008 11:11 AM

I think the '83 must be a little different from my '81, i don't show that hose number..but i get the idea

any tricks to removing the spider? At first glance i thought you have to disconnect the "legs" but i see from your pictures that you dont

Danglerb 08-01-2008 11:35 AM

My old spider boots were very hard, so I cut them off after wrassling a few. In theory loosen all the clamps, spray with silicone lubricant, and slide on to the leg, which is how they went back on. the body/leg doesn't have much of a gap, but its not really a tight fit getting the body in and out.

Next time I do it I will put both clamps of the throttle body rubber sleeve on the intake body, top one tightened to final tightness, bottom one just enough to hold on, then once its on the throttle body I will loosen the lower clamp and let it slide down where it should go and then tighten. Last time I put the clamp on the throttle body first and it was a bear to get the upper clamp where I wanted it on the body.

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