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I'll get you started...the sensor in the air cleaner controls the flap inside the snorkel. 1 hose to the sensor comes from vacuum, the other goes to the activator on the snorkel. When it's cold the flap closes, and heat comes up the tube (probably missing) to heat the air inside the cleaner. The default position is open. You really need a schematic, and you REALLY need a Chassis manual to understand and sort this out. Maybe somebody can post a pic. I type slow, so I really don't want to get into the manifold sensor.
See if these help. The vacuum port at the rear is full vac for the auto trans modulator. On the vacuum tree, top to dist. middle to carb and bottom to a full vac port on the front of the manifold.
The thermal vacuum switch in the intake controls vacuum to the distributor vacuum advance. There are three ports, labeled D, C, and M for Distributor, Carb, and Manifold. Your car uses ported vacuum for the vacuum advance. This means that vacuum for the distributor is normally pulled from a port on the carb that is just ABOVE the throttle plates at idle. That means that vacuum and thus advance is zero at idle and small throttle openings. As soon as the throttle is opened enough to uncover this port in the venturi, the vacuum signal goes to full manifold vacuum. This was done primarily as an early emissions control. Unfortunately, with no vacuum advance at idle, the engine can overheat at low speeds. The TVS senses that and if engine temps get too high, it switches the distributor from ported ("C") to straight manifold ("M") vacuum. This increases advance at idle and lets the engine run cooler.
You might ask yourself, why even bother with ported vacuum if the car runs better on manifold vacuum? Excellent question. I eliminate the TVS and run straight manifold vacuum at all times.
The thermal vacuum switch in the intake controls vacuum to the distributor vacuum advance. There are three ports, labeled D, C, and M for Distributor, Carb, and Manifold. Your car uses ported vacuum for the vacuum advance. This means that vacuum for the distributor is normally pulled from a port on the carb that is just ABOVE the throttle plates at idle. That means that vacuum and thus advance is zero at idle and small throttle openings. As soon as the throttle is opened enough to uncover this port in the venturi, the vacuum signal goes to full manifold vacuum. This was done primarily as an early emissions control. Unfortunately, with no vacuum advance at idle, the engine can overheat at low speeds. The TVS senses that and if engine temps get too high, it switches the distributor from ported ("C") to straight manifold ("M") vacuum. This increases advance at idle and lets the engine run cooler.
You might ask yourself, why even bother with ported vacuum if the car runs better on manifold vacuum? Excellent question. I eliminate the TVS and run straight manifold vacuum at all times.
Damn Joe!! Thanks for the detail, I sincerely appreciate it.
Therefore, does that explain why mine is not connected, because it is not needed? For aesthetics, can I remove and plug it?
Damn Joe!! Thanks for the detail, I sincerely appreciate it.
Therefore, does that explain why mine is not connected, because it is not needed? For aesthetics, can I remove and plug it?
If your distributor is connected directly to manifold vacuum, yes. If it's connected to ported vacuum on the carb, either move it or reconnect the TVS.
I know this is an old thread but an update would help me a lot.
My setup is a 69 455. There are 4 vacuum lines all individually ported to the intake manifold. The front line shown in the first pic goes to the TH400 trans. The other three lines in the second pic are connected to the brake booster , distributor and cannister. The Quadrajet is plugged.
So, Is this a proper and effective way to run these lines ? The car has been sitting while under construction. It runs well when cold but poorly when warmed up. When I I shut it down it will often not start until it cools down a bit.
There is also a brake issue. The pedal returns fine when the ignition is off but must be pulled back by foot when the car is running. I suspect based on other threads I have been reading that the booster is at fault. The booster was new when installed but sitting a lot during the build. It is a 9" which may have been a mistake as well.
My plan is to disconnect the brake booster vacuum line and block it at the manifold to "put aside" the brake issue for now.
So while I trouble shoot these issues does the vacuum line setup as shown appear correct ?
Your vacuum connections are fine. I assume that the second small line behind the carb is for the A/C. You currently have vacuum advance running from full manifold vacuum. That is not a problem if the engine runs well. If you want to try ported vacuum, that's the port at the front driver side of the carb.
Your hot running problem sounds like a choke issue, not vacuum lines.
Your vacuum connections are fine. I assume that the second small line behind the carb is for the A/C. You currently have vacuum advance running from full manifold vacuum. That is not a problem if the engine runs well. If you want to try ported vacuum, that's the port at the front driver side of the carb.
Your hot running problem sounds like a choke issue, not vacuum lines.
The two small vacuum lines on the back side are one to the distributor one to the black cannister (vacuum tank) on the firewall. So for ported vacuum it would run from the carb front drivers side , currently plugged, to the distributor and would eliminate one small port of the three in the back correct ? and what would be the gain/ change ?
It also appears to be running rich, so would the choke be suspect there as well ?
Last edited by Bitburger; October 24th, 2020 at 05:36 PM.
The two small vacuum lines on the back side are one to the distributor one to the black cannister on the firewall
The black canister is the vacuum reservoir for the A/C.
So for ported vacuum it would run from the carb front drivers side , currently plugged, to the distributor and would eliminate one small port of the three in the back correct ? and what would be the gain/ change ?
At the risk of inciting yet another ported vs manifold vacuum discussion, the fundamental difference is that ported vacuum does not provide any advance at idle and small throttle openings. Manifold vacuum does. The latter will typically result in a smoother idle and crisper response, but at the expense of possible pinging. You can swap them and see which the engine likes better, but you may have to tweak the initial timing to optimize total advance.
It also appears to be running rich, so would the choke be suspect there as well ?
July 28th, 2017, 01:37 PM
