Engine Part Identification

[chuddy]

Anyone know what this is? I'm sending this engine in as a core and have never seen this before:

 

[Chiclassics]

I think its a throttle/idle control actuator

 

[DirtDonk]

It's what's left of the vacuum advance controller thingy.
Given it's size, shape, and especially where it's mounted (back of intake, near vacuum manifold (tree)), it's a '69-ish to '73-ish advance controller.
I might have the years wrong. Could've been earlier and later.

You'll find discussions of it here, with pictures of the complete part and maybe even vacuum diagrams. It was connected to both manifold and ported vacuum if I remember, and was used in conjunction with distributors that had dual-diaphragm vacuum advance canisters.

Part of the fledgling smog control systems.
Kind of a pain sometimes, but needed in an accurate restoration. Most of us that had them back in the day, missed our single diaphragm advance distributors, and went in that direction when we could. Eliminating the finicky dual version.
I'm not a fan of just willy-nilly removing any and all smog equipment. But that was one of the ones that did not seem to bring any downside to changing it out.

Paul

 

[Viperwolf1]

That is the transmission regulated spark solenoid vacuum valve.
Nope. I misidentified it. I think James is right with the distributor vacuum advance control valve. At least I had a picture of it.

Vacuum/Electrical Question

The attached foto is of a switch/valve that is electrically connected but has no vacuum input or output. The Bronco seems to be running fine without it, but the question is, what is it, and how should/where should the vacuum connections be routed to? Or should I eliminate it completely? This...

classicbroncos.com

 

[DirtDonk]

I think there's a mixup of parts in that previous discussion.
The first post shows the transmission/ambient switch thingy. Also included later in that discussion, is a picture of the same device in question here.
Which I still maintain is the vacuum-only, advance/retard control valve.
Nothing to do with the ambient switch system, which was only in '72/'73 models anyway? I think I have the years correct. But '73 for sure.
If you find a picture of the vacuum control valve with it's blue plastic cover intact (covers the spring) you can find it in the vacuum diagrams for different years.

Paul

 

[jamesroney]

I think there's a mixup of parts in that previous discussion.
The first post shows the transmission/ambient switch thingy. Also included later in that discussion, is a picture of the same device in question here.
Which I still maintain is the vacuum-only, advance/retard control valve.
Nothing to do with the ambient switch system, which was only in '72/'73 models anyway? I think I have the years correct. But '73 for sure.
If you find a picture of the vacuum control valve with it's blue plastic cover intact (covers the spring) you can find it in the vacuum diagrams for different years.

Paul

Hey Paul, You are mostly correct. (I would say 100% correct, but then somebody would tease me for being a know-it-all and accuse me of using AI, and I would go sulk and delete all my posts...)

But yes, the C8AF-12A111-C is in fact the Distributor Vacuum Advance Deceleration Control Valve. It is part of the Improved Combustion (IMCO) system, and as you noted...it has a limited function.

It is a C8AF part, so designed for 1968+, and seen on the Bronco from 68-71? Somebody with a MPC can figure it out exactly...but it is not part of thermactor...it's part of IMCO.

The valve is intended to provide additional ignition advance in the situation where the throttle is snapped shut on deceleration. During sharp, snap Decel, there is an excess of raw fuel in the manifold, and a sharp rise in intake vacuum. This creates a temporary rich condition at the exact moment that the vacuum signal from ported vacuum (spark port) goes away, and manifold vacuum on the retard side of the dual diaphragm advance spikes up. So the distributor snaps to full retard. This un-burned fuel can result in an exhaust pipe backfire. (technically not a back fire, but more of a "after-fire" or exhaust pop, but you know what I mean...)

In order to mitigate the potential for exhaust-pop on decel, the spring loaded delay valve waits until the manifold vacuum spikes above spark port vacuum. Then it moves the plunger off it's seat against the spring, and returns back after about 2-3 seconds. A lot of people get this wrong, because they look at the dual diaphragm canister on the distributor and think that if it has the same vacuum on both sides...it must be in neutral. But the diaphragms are different sizes for advance and retard. So if you put the same vacuum on both sides, it will move towards the advance side. That's the magic.

And yeah, if you delete it...you would never know. And it's useless with an automatic trans. Hope that helps.

Here's a pic shamelessly pirated from Ebay. Funny thing is that I seem to remember the cap being a different color.

 

[Oldtimer]

MPC indicates 68 thru 71 depending on flavor of Bronco (U).

*James, I appreciate your version of AI (Accurate Insite).

 

[dmoses42]

My '72 has it, mostly intact. If the piece Viper's pic shows attached to the front of the left valve cover is the Air Bypass Valve, I have all of it. It wasn't fully plumbed with the vacuum lines, and the electrical connections were unhooked except for the spades on the Bypass Valve.

 

[jamesroney]

My '72 has it, mostly intact. If the piece Viper's pic shows attached to the front of the left valve cover is the Air Bypass Valve, I have all of it. It wasn't fully plumbed with the vacuum lines, and the electrical connections were unhooked except for the spades on the Bypass Valve.

Are you sure?

The Thermactor bypass valve is not part of the D2OZ-7E440-A Transmission Regulated Spark Valve or system. The bypass valve is also called the diverter valve, and is part of the smog pump system. It is a completely mechanical valve, and should have no wires ?

The Transmission Regulated Spark circuit is the TRS, and it has three components. A grounding switch in the transmission, a door pillar mounted temperature switch, and a valve cover mounted solenoid valve. When the outside temperature is below 49 F, the switch opens, and defeats the system. When the door post is above 65 F, the switch closes, and the system is enabled.
If the system is enabled, (above 49F sometimes, and always above 65F) AND the transmission switch is grounded...(3rd gear only) then the solenoid valve is OPENED, and the vacuum advance is allowed to function. The purpose of this valve is to ensure that your Bronco runs badly, overheats, and stumbles in every gear except 3rd...on days when it's nice outside.

This is the first thing that should be removed or defeated by every Bronco owner in every situation. There is no scenario where your life will be improved by having this device function as designed. The best thing that ever happened was to eliminate it. Funny thing is...if you just unplug it electrically, it makes it worse, because then it stumbles and overheats and runs badly in EVERY gear.

Here's a pic of the 72-73 trans with the 3rd gear switch. and the TRS valve. (TRS = Truck Runs Sh*tty)

 

[dmoses42]

Ahhh... Then the TRS is what was unhooked. I took it off just trying to clean up the engine bay, since it wasn't wired in anyway. And no switch in the transmission, I replaced it with a reman unit from Jeff's back in the 90s because the synchros were shot in the original. And while it does have the Vacuum Control Valve, it doesn't have the Bypass Valve and the "red stripe" vacuum hose isn't connected to the distributor, it is plugged with a screw, up near the distributor.

 

[DirtDonk]

Are you sure?

Yes
We had 3 72 Broncos in our group, two CA spec and one FED spec, and all three had the ignition advance controller.
So, including my 71, that made four of the controllers that were disconnected almost immediately after ownership was taken over.
It wasn’t that we didn’t want clean air, but coming from older vehicles it was extremely annoying to let off the gas and have the engine stay at a higher RPM.
Upshifting wasn’t too bad, but it made slowing down under engine braking in heavy traffic, quite annoying.
I still have my original one in a drawer.

 

[jamesroney]

Yes
We had 3 72 Broncos in our group, two CA spec and one FED spec, and all three had the ignition advance controller.
So, including my 71, that made four of the controllers that were disconnected almost immediately after ownership was taken over.
It wasn’t that we didn’t want clean air, but coming from older vehicles it was extremely annoying to let off the gas and have the engine stay at a higher RPM.
Upshifting wasn’t too bad, but it made slowing down under engine braking in heavy traffic, quite annoying.
I still have my original one in a drawer.

The “are you sure” was for @dmoses42 on the diverter.

Wasn’t doubting you.

 

[DirtDonk]

 

[Chiclassics]

So it avoids the pop on sudden deceleration- something new to learn everyday.