Vacuum Help - I am trying to figure the vac lines on my 79 trans am

[TAKerry]

Sorry if this is not in the right spot, figure best exposure. A while back there was someone discussing vac lines in their car. One of the members knew a good deal and I made a comment to them about needing advice in the future. I apologize as I cannot remember whom it was, I will blame it on age, LOL. Anyway, I am trying to figure the vac lines on my 79 trans am, I have some idea but still a few questions. If the person that may remember the original comments is available please send me a pm. Thanks. 

 

[joe_padavano]

400 Pontiac or 403 Oldsmobile?

 

[TAKerry]

400 pontiac motor, 4 speed manual transmission.

[joe_padavano]

[TAKerry]

Thanks, one of the things I was looking for was the distributor hook up.

Also, at the top of the diagram there is a item marked ds-tvs. Is this the port that is screwed into the block? 

tvs=thermal vacuum switch ?

svb=?

ds=?

efe=?

egr=?

ds-vmv=?

 

I am not running the emissions stuff. I do have the vapor canister though so those are not a problem. The line going to the efe valve (I believe this is the exhaust) is not needed. So I assume I can just leave that out?

 

There is only a single port coming off the back of the carb which hooks to my brake booster. Looks like I need to replace that with a multi so I can attach a line to the tach?

 

I see the colour shading on the lines but what is the difference between the ported and manifold?

 

[John348]

Ported vacuum only means that that particular outlet will receive vacuum based on the position of the throttle, so in this case there would no or very little vacuum at idle. Manifold or main vacuum is constant supply of vacuum. 

[joe_padavano]

2 hours ago, TAKerry said:

Thanks, one of the things I was looking for was the distributor hook up.

Also, at the top of the diagram there is a item marked ds-tvs. Is this the port that is screwed into the block? 

tvs=thermal vacuum switch ?

svb=?

ds=?

efe=?

egr=?

ds-vmv=?

 

I am not running the emissions stuff. I do have the vapor canister though so those are not a problem. The line going to the efe valve (I believe this is the exhaust) is not needed. So I assume I can just leave that out?

 

There is only a single port coming off the back of the carb which hooks to my brake booster. Looks like I need to replace that with a multi so I can attach a line to the tach?

 

I see the colour shading on the lines but what is the difference between the ported and manifold?

 

TVS is thermal vacuum switch - it opens or closes vacuum ports depending on coolant temp.

EFE is early fuel evaporation, which is the heat riser in the exhaust manifold outlet that closes when the engine is cold to route exhaust through the crossover under the carb to promote fuel vaporization. Newer cars used a vacuum actuator rather than the old bimetallic spring.

EGR is exhaust gas recirculation, which is the vacuum operated valve typically bolted to the exhaust crossover on the intake manifold, next to the carb.

 

The EFE&EGR-TVS shuts off vacuum to both of those systems until coolant reaches a certain temperature.

 

DS stands for distributor source, which is the vacuum source that controls the vacuum advance

VMV is vacuum modulator valve, which blends two different vacuum sources to achieve the desired vacuum signal to the vacuum advance can.

 

The emissions controls use a combination of a thermal vacuum valve (DS-TVS) and a vacuum modulator (DS-VMV) to obtain the correct vacuum advance curve depending on engine temperature and load (engine vacuum is an indicator of load on the engine).

 

SVB is secondary vacuum break, which is typically a vacuum diaphragm that controls either choke opening or secondary air valve opening (or sometimes both on a Qjet). That SBV-TVS is the thermal vacuum switch that provides vacuum to the SVB once coolant reaches a certain temperature.

 

As noted above, manifold vacuum is the vacuum level inside the intake manifold. Ported vacuum (also called timed vacuum) is sourced from ports slightly above the throttle plates in the carb. With the throttle plates closed, there is zero ported vacuum. As you start to open the throttle, the throttle plates uncover these ports, which then see manifold vacuum. The timing of this can vary depending on where the ports are relative to the throttle plates. Some carbs have more than one set of ports in the throttle bore to provide vacuum signals with different timing relative to throttle position.

 

It pains me to say this, but the complexity of these vacuum-operated emissions controls suggests that computer-controls are the better way to go. A throttle position sensor, coolant temp sensor, and MAP sensor pretty much give you all the info you need.

[TAKerry]

Thanks Joe.  That is all valuable information.  

[TAKerry]

Sorry, thanks to John as well!!

[TAKerry]

Hi Joe, here is a pic of the tvs I was talking about. This one screws into the block on the pass side of the motor.

20240216_143028 by Kerry Grubb, on Flickr

It has 3 markings 

MT - port closet to mounting point

C - middle port

D - port farthest from mounting point

 

This is the one that came off of my motor. I have a replacement ordered, hope its correct should be here in a few days. I have the layout diagram, and I think I have my head wrapped around things better now than before. I was curious as to what the markings mean. I only assume the MT is for manual transmission but I am pretty sure there are no vacuum hooks up on that part itself.

 

Kerry

 

[rocketraider]

C= carburetor. This connects to a ported vacuum source from above the throttle plates

 

D= distributor. It runs from the TVS to the distributor's vacuum advance can.

 

MT= manifold vacuum from one of the intake manifold runners.

 

This is a 74 Olds TVS. The other Divisions that use TVS are similar.

 

[TAKerry]

Thank You Glenn.

 

[rocketraider]

You're welcome.

 

Forgot to add the TVS sits in an engine coolant passage. Normal coolant temperature, Distributor vacuum advance source is Carburetor ported vacuum. High coolant temperature, a pill switch in the TVS moves and changes the vacuum advance source to full Manifold vacuum. This advances timing (and idle speed) a few degrees which will theoretically help cool the engine.

 

The only one of my cars I've ever noticed that happening is the Toronado, but they tend to run hot anyway.

[joe_padavano]

Glenn beat me to it.

[rocketraider]

Well that doesn't happen often!😛

[Paul Dobbin]

All good information.   About 10 years ago my original 81 El Caamino stated running rough and I replaced all the original vacuum lines.

Looks like black spaghetti under the hood.  But ot sure runs better now.

[rocketraider]

Here's a discussion on the BT-7002 tester. I wanted this thing bad when it was offered for sale last year. Only one I've ever seen that was complete and never found out who bought it, though I've wondered if it's living in Northern Virginia now!

 

https://classicoldsmobile.com/forums/miscellaneous-classifieds-84/oldsmobile-engine-tester-kit-169378/

[joe_padavano]

Fred has all the cool toys. 😁

[TAKerry]

I finished getting everything put together yesterday. Well, almost everything. I found the 'correct' vac tree off the carb (the one I have is hooked up and will work, its all that is available new but its not 100% right). I expect it towards the end of the week as its coming from across the country. I also need to hook up the lines to the charcoal canister but its not installed yet (I left the core support off for easy access), tubes are there. AND I need one more length of tubing gonna see if napa has that today. But all of the routing is figured out and ports are in. One of the hurdles was that NO one has these parts anymore. I tried all of the local shops, and even the Pontiac suppliers dont have the exact parts needed, just chineseum knock offs that might be close. I got some stuff from Franks in Cali. and a couple of guys that have a pile in their shops. Again thanks for all of the help. Its awesome to have some knowledgeable people across a wide variety of subjects on this forum. The car I am working on is 1979. I have a 1977 service manual and a 1980 service manual. I have not found one for 1979 yet. The motor is more in keeping with the 77 but there are still some slight differences. I had the vac diagrams but without knowing the proper nomenclature I had no idea what they were, let alone what they did. I asked a lot of questions on another forum as well as talked to 'motor

 people' even with a person that has the same settup as myself with a fresh high end rebuild. A lot of the answers were to the tune of 'I dont think that part is important, this is the way my guy did it, no idea what that is for but its there etc.' I am far from an expert but at least I now know what a TVS is and have a basic idea of how things work. THANKS AGAIN!! 

[rocketraider]

1 hour ago, TAKerry said:

I finished getting everything put together yesterday. Well, almost everything. I found the 'correct' vac tree off the carb (the one I have is hooked up and will work, its all that is available new but its not 100% right). I expect it towards the end of the week as its coming from across the country. I also need to hook up the lines to the charcoal canister but its not installed yet (I left the core support off for easy access), tubes are there. AND I need one more length of tubing gonna see if napa has that today. But all of the routing is figured out and ports are in. One of the hurdles was that NO one has these parts anymore. I tried all of the local shops, and even the Pontiac suppliers dont have the exact parts needed, just chineseum knock offs that might be close. I got some stuff from Franks in Cali. and a couple of guys that have a pile in their shops. Again thanks for all of the help. Its awesome to have some knowledgeable people across a wide variety of subjects on this forum. The car I am working on is 1979. I have a 1977 service manual and a 1980 service manual. I have not found one for 1979 yet. The motor is more in keeping with the 77 but there are still some slight differences. I had the vac diagrams but without knowing the proper nomenclature I had no idea what they were, let alone what they did. I asked a lot of questions on another forum as well as talked to 'motor

 people' even with a person that has the same settup as myself with a fresh high end rebuild. A lot of the answers were to the tune of 'I dont think that part is important, this is the way my guy did it, no idea what that is for but its there etc.' I am far from an expert but at least I now know what a TVS is and have a basic idea of how things work. THANKS AGAIN!! 

How important the emissions components are depends on two things. 1) what level of restoration accuracy you're going for and 2) how tight your area is on emissions testing.

 

Your 400 would run very well on ported distributor vacuum only. But looking at Joe's emissions diagram you about have to have the EFE/EGR thermal vacuum switch to make the exhaust heat riser work, otherwise the engine would be hard to live with on a cold start.

 

On 2/5/2024 at 4:48 PM, joe_padavano said:

That's where a lot of folks mess up. The very idea and concept of any emission controls pisses them off and they start disconnecting and bypassing stuff. They don't stop to think it's designed to work together and bypassing one component can cause another one that's tied to it to not work. That in turn creates another driveability problem.

 

I think some of it was overkill too, but the Feds mandated it so the carmakers had to do it to be able to sell their product.

 

Joe's point about computerized controls is a good one, but all that was available was rudimentary stuff and its long-term reliability hadn't been proved.

 

To put that in perspective, any cheap smartphone has more computing power than the first space shuttles.

 

The parts are out there. Knowing what it's called, what it does, and armed with a part number you should be able to find them.