VAC control Modules, pinging

[Yank Yarborough <102557.1565@domain.elided>]

On Thu, Nov. 20, Rob Hughes wrote:

>Yank,
> Are you talking about the Ported Vacuum Switches?  My 75 Scout II
>vacuum hoses are routed through two temperature controlled vacuum
switches.
>They are about the size of spark plugs, and screw into the manifold, one
on
>each side.  Each has ports on it for vacuum hoses (as far as I can tell
>they only need two ports -- one in and one out -- for my vacuum system,
but
>one of them has three and the other four, which suggests they are not
>stock).  I've been unable to find replacements for these, but I think the
>accepted name for them is Ported Vacuum Switches.

On the vac diagram under the hood of my 79 Scout II they are called Vacuum
Control Modules. The high temp control module (passenger side of manifold)
on my 79 has 3 ports, and the low temp module (drivers side of manifold)
has two ports. I haven't had a chance to look at my 73 yet.

>They are supposed to open (allow the vacuum signal from the carb to go to
>the component) at a certain temperature, which may be stamped somewhere on
>the body of the switch, or I think some of them are color-coded.  One of
>mine transmits the vacuum signal to the EGR valve, and the other (I think)
>transmits vacuum to the air intake flapper.  Neither seemed to be working,
>so I checked them by removing them and sticking the bottoms in a pot of
>water on the stove.  I monitored the heat, and periodically applied vacuum
>with my pump to one of the ports, checking for vacuum at the other ports.
>No vacuum ever got from any one port to any other port, even at well over
>150 degrees.  I concluded that they just didn't open.

I checked the high temp vac control module on my Scout and found that it
only has vacuum immediately when the throttle plates open. I plan to check
the low temp module when I get a chance, but it had 0 vac when the engine
was hot. I don't know if this is the way the modules are supposed to work
for sure.You may want to check your high temp control module again to
determine if it has vacuum when the throttle plates open.

While I had the vacuum guage out, I checked the vac on my engine. I had
been told by folks in the past to set the carb up so that the highest
possible vacuum was obtained. I ended up turning the mixture screws on my
Carter Thermoquad out about 1 full turn to get the highest vacuum. Now I
only experience pinging at wide open throttle (even after the 4 barrel
kicks in). Also, the deiseling (engine run-on) I was experiencing is now
gone! Could a lean mixture have caused this before?

Later,
Yank