1979 Spark / EGR ports

[Driftwood]

My 2100 Autolite carb appears to only have a Spark (S) vacuum port.
A Spark CTO switch routes vacuum from the S port to the distributor advance.
But I do not appear to have a Spark CTO switch anywhere on the intake manifold.
Soooo, my distributor advance is hooked up directly to the S Port.

My 2100 Autolite carb does not have a EGR (E) vacuum port.
My EGR CTO switch directs vacuum from the E Port to the EGR valve.
Again, there is no E Port on my carb.
So the EGR valve is hooked up directly to manifold vacuum.

How my jeep runs seemingly fine is a mystery to me.

79-FSJ-360_Vacuum.jpg

[Driftwood]

I think I found the EGR CTO switch, or whats left of it. It appears to be broken off. Its located on the PAX rear side of the intake.

Refer to part # 4704.1 in this pic.

[tgreese]

Sounds like you have it figured out - forgive me it I go on here and you don't need the input.

You understand the difference between manifold and ported vacuum? Ported may be called distributor or spark vacuum. Ported vacuum is manifold vacuum that is mechanically blocked at idle. The closed throttle plate blocks the vacuum port , so vacuum drops to zeroish. Manifold vacuum is high at idle. Any ported vacuum port must come fromt he base of the carburetor, since its action requires proximity to the throttle plates.

You can plumb this stuff any way you want, as long as the logic of the connections is correct. If your carb only has one spark port, use a tee. (I'd suspect that it's a reman and they subb'd a carb body with one fewer port. No big deal.) Put the CTOs in whatever holes in the water jacket the engine provides.

I would expect your spark CTO to have 3 ports and be located at the front of the engine, ie in the water outlet. I'd expect your EGR CTO to be at the back of the engine, and have two ports to cut off EGR when the engine is cold. I'd also point out that the spark CTO is 100% emissions targeted. Its objective is to retard the spark at idle, which lowers the combustion temperature and reduces NOx emissions when idling. Added advance when cold improves the idle, which helps cold-start driveability.

Also, your missing a spark CTO may explain why your engine runs fine with the EGR on manifold vacuum. Normally an EGR valve open at idle will make a rough idle. This can happen when the EGR valve pintle accumulates carbon and sticks open. With added advance at idle, your engine may idle ok even with the charge diluted by exhaust gas. Or it may be your idle mixture is so rich that the dilution does not matter.

[Driftwood]

My 2100 Autolite carb appears to only have a Spark (S) vacuum port.
My 2100 Autolite carb does not have a EGR (E) vacuum port.
79-FSJ-360_Vacuum.jpg

So apparently after researching the Identification Tag affixed on my 2100 Carb, I've determined that it is a 1972 model 2100 for a 304 V8 equipped with a Manual transmission.

The Code on it reads

2DM2
B H1 9

B = Vendor
H = August
1 = Year manufactured, 1971
9 = Day manufactured
---------------

My 2100 carb appears to have been manufactured on 9 August 1971.

[rang-a-stang]

Here was how 79 was configured (I had to really study this to get mine through smog, pre-EFI).

The EGR CTO should be in a brass block in the passenger side rear of your intake that also has the heater hose that leads to the heater core coming out the top. On 79's that is a 2 port CTO (and I think it is supposed to be white). It is closed when the engine is cold, then opens when the engine warms up. Basically it disables your EGR when the engine is cold. On CA models there is also a modulator on there that really helped with an off idle bog on mine. if you need that modulator, let me know, I still have it.

The spark CTO should be on the front passenger side threaded directly in the manifold coolant passage. It is a 3 port and should be yellow. The middle nipple goes to your advance can on your dizzy. This CTO has ported vacuum on one nipple and manifold vacuum on the other. When the engine is cold, the CTO provides manifold vacuum to the dizzy, then when you get up to operating temp, it switches to ported vacuum.

SOOOoooo with all that said:
A) if you have no EGR CTO, then you are either always running EGR whether cold or not (vacuum line is hooked up, EGR Valve still works) or you are never running EGR (No vacuum signal hooked up and/or your EGR valve is faulty).
B) Your truck will run great on either ported or manifold vacuum. If it is running correctly as is, I would ignore this CTO. If you need one, I have one in my stash I will send you.

[Driftwood]

Rang
Yes, for my 49-State 360, there WAS a EGR CTO in the brass block in the passenger side rear of my intake. But all that remains of it is the threaded brass insert in the brass block. The 2 port portion of the EGR CTO is gone (Broken Off?). I purchased a "Standard" brand 2 port EGR CTO and installed it in the front passenger side. My EGR valve is now receiving ported vacuum from the S port on my carb via the new EGR CTO.

I've determined that my carb is a 1972 era 2100 and it does not have a E port.

My 3 port yellow Spark CTO was installed on the front passenger side. There were no vacuum lines attached to it. In the diagram below, the 3 port Spark CTO is installed in the thermostat housing. My thermostat has a plug. The plug is so old that I am unable to remove it and am only stripping the head of the plug. I may have to get a new thermostat housing.

With that said, my two CTO's are installed in different locations from what is detailed in the below 1979 49-State 360 vacuum diagram.

Maybe I should just install my new EGR CTO into the location you described and be done with it.


Thoughts?

.

[Driftwood]

My 1979 Technical Service Manual states the 3 port Spark CTO Switch is located in either the thermostat housing OR intake manifold. MORE CONFUSION!

Removal—Eight-Cylinder Engine
(1) Drain coolant from radiator.
(2) Remove air cleaner assembly.
(3) Code vacuum lines and disconnect from CTO switch.
(4) Using 7/8-inch open end wrench, remove switch from thermostat housing or intake manifold.

Installation—Eight-Cylinder Engine

(1) Install spark CTO switch in thermostat housing.
(2) Connect vacuum lines to switch.
(3) Install air cleaner assembly.
(4) Install coolant.
(5) Purge cooling system of air.

[tgreese]

Lots of TSM verbiage and illustrations are recycled from previous years. A few grains of salt may be needed.

[rang-a-stang]

If your truck is running well I would leave it.