I noticed on my 71 that the distributor vacuum control switch only has 2 nozzles. I couldn't find one like it shown in some of the discussion threads on here. It's a 455 4-speed. I'd say maybe that's the difference, but the service manual figures don't support what I have per what's shown in the figures, specifically 6K-19. I had noticed my OAI flap door wasn't plumbed, so I started looking more and discovered this too. Love to hear any comments. If anyone can share some photo's of their vacuum lines for a 71 455 4-speed I'd be grateful. The figures in the book are ok, but not as good as real life.

 

It appears (operative term) to me you have the incorrect DVCS installed in your intake manifold. It appears you have a 2-port thermal vacuum port switch & this is where I'm on shaky grounds. I've seen them (2-port), have never changed/installed or worked on one. I'm not certain what engine(s)/intake manifold(s) they were used on. I think maybe 1977, 1979 and sometime in the mid-80s? I remain of the opinion none-the-less, the correct DVCS for your 455 intake manifold is the 3-port DVCS which includes the electrically activated solenoid. End of day, I "think" someone installed the incorrect DVCS onto your 1971 455 intake manifold. They "may" have had a reason for this perhaps based upon carburetor type & or type of OAI? I really can't say, others may provide more information.

This is what a typical 1971 TCS/DVCS looks like and I believe in 1971 it made no difference if it was either manual or automatic. I believe you already know this from the 1971 CSM; yet, the one you have pictured in your image is incorrect for a 455 intake manifold and as far as I know they only deltas were in vacuum hose configuration(s) based upon AC and/or 2-bbl vs. 4bbl.

 

I'll add to this at the end of the day, I don't how that 2-port thermal vacuum switch you have installed actually operates on your intake manifold and further is it even functioning? Many of us have deleted the TCS/DVCS altogether.

 

This appears more likened to what I see in the image you posted - sorta/kinda.

 

I think the electrical connection was added in 1971, and in 1970 it was only a thermal / vacuum switch. Note that those had 3 hose nipples so apparently not what’s on the OP’s car.

https://classicoldsmobile.com/forums...switch-178835/

 

That 2-port switch you pictured does look like it. I see the replacement versions don't have the electric connection on top at all. A few other posts I've seen speak to these. I also found a couple reply's by you, Chief, in those. I may try to switch for a bit and see before deleting.

Long story with this car, I've not had it with me for very long and I'm just getting into looking at missing items and problems.

Thanks for the replies.

 

The valve Norm showed in post #2 is correct.

 

So, the one available today (assuming the cutaway is accurate to the switch) without the electric connections just deletes the vent line?

 

What do you mean by "the one available today without the electric connections"? As Kenneth pointed out the 1970 TCS/DVCS had no electric solenoid. Is it available today? I have no idea.
"If" you're referring to a 2-port thermal switch such as what "appears" to be installed on your intake manifold, I don't know how the internals of that 2-port switch are configured therefore I can't address your question whether that switch simply deletes the vent hose.


FWIW, some of the members generally have available (advertised in the Parts for Sale classifieds) the 3-port switch as illustrated in Post #2 which is correct for your car. I could see there may exist the possibility someone removed the OEM original wiring which would have connected to the correct OEM 3-port TCS/DVCS to the transmission. Is that possibly partly the reason for your question?

 

The OEM valve with the solenoid combines TWO separate functions into a single valve. The solenoid valve blocks vacuum to the distributor in all forward gears except high gear. This was the Transmission Controlled Spark system that was an early emissions control device intended to reduce NOx emissions. The lower part of the OEM valve is designed to prevent engine overheating at low speeds. Normally the distributor was connected to ported vacuum. If the coolant temp exceeded a certain level, the valve would open up and connect the distributor directly to manifold vacuum. This provided more advance at idle and low speeds, which both reduced combustion temps and sped up idle speed so the fan would move more air through the radiator.

The second valve without the solenoid simply performs the latter function. It was used on some 1966-69 cars by itself. It was also used in 1970 in conjunction with a separate solenoid valve for the TCS system. The 1971-72 valve simply combined these two parts into a single unit to reduce cost. Functionally the 1970 and 71-72 systems are the same.

 

Is the original 71-72 combo valve unobtanium? RockAuto just shows the same part the OP has installed on his motor.

 

One more time: RockAuto is NOT a reliable source of part fitment, especially for Oldsmobiles. No one reproduces the 71-72 valve. Good used ones are not cheap

 

May be available...

'71/72 TCS Switch (on intake manifold) - nice "restored"

 

Good info.

Thanks for the link. There's a couple on eBay currently too. One about the same cost, the other cheaper with a dinged up nozzle.

 

Adding something on to this thread that was a discovery as I pulled the electrical tape off the control switch connector this weekend. It'd been taped up and kept back in the firewall clip since I've had the car. I just finished putting everything back together and discovered this guy in there. I'm guessing that was someone's fix??? I also noticed what I think is the other end of this run's connector, which I believe goes to the trans (manual in this case) was wire tied up dangling. It's the same colors as the switch's connector has, so that's my assumption. I'm thinking I need to pull this resistor out?!? There's also nothing on the clip or the sensor's blades to give me indication of the clips orientation, so I'm guessing it doesn't matter to the function.

 

The switch is part of the Transmission Controlled Spark system, which was a prehistoric emissions control system first used on the 1970 cars. The purpose of TCS was to inhibit vacuum advance unless the trans was in high gear to reduce NOx emissions. The wires to the trans plug into a switch that senses the trans is in high gear (a pressure switch for ATs and a physical switch for MTs). The switch is normally closed in all gears except high, which energizes the solenoid in the valve and prevents the vacuum signal from reaching the distributor. In high gear the switch opens, which de-energizes the solenoid and vacuum advance operates normally. Disconnecting the wires at the trans or at the vacuum switch prevent the solenoid from operating, which disables the TCS function and provides vacuum at all times, just like on non-emissions-controlled cars. The valve has a secondary function, which is to switch the vacuum advance from ported to manifold vacuum if the engine starts to overheat at idle or low speeds. This is independent of the TCS operation and is something you want to retain. The thermal function does not require the electrical connection to work properly. When EGR became federally mandated for the 1973 model year, it superseded the need for TCS, so the TCS system was dropped after 1972.

 

Some ascribe to the belief that one should just plumb the vacuum advance to manifold all the time and be done with it.

 

Except that you need to understand what the vacuum advance curve is. If the distributor isn't set up for full time manifold vacuum, you may have to retard initial timing to avoid pinging, which then reduces total timing, which hurts power unless you change mechanical advance.

 

I was curious about the component sticking out of the connector on top of the switch, I can't believe that would be factory, but these days weird stuff is prevalent. I'm at the leave it or pull it stage.

 

What "component"??? Which pic (posting #). If you mean the resistor looking thing that is correct....the factory typically had a piece of black tape wrapped around that part of the wiring sort of protecting that resistor, etc. Most likely black CLOTH tape around it.