I'm hoping to create a thread that will become a sticky to help people understand the vacuum control system and restore any and all vacuum control systems on their truck be it for drivability, emissions, inspection, etc.

EGR

The EGR system is frequently disabled for no cause. It has no impact on performance and in stock form is responsible for increased mileage. It's vacuum operated and not operational at idle or WOT. EGR is part of the emissions system and is used to reduce HC and NOx emissions. The system replaces some of the combustible air with an inert gas from the exhaust. This both cools the air/fuel mixture and allows the engine to operate as if it were a smaller displacement than it really is and use less fuel. Less fuel used reduces hydrocarbons, but without the EGR gas the lean mixture causes a hot burn that raises NOx. Dirty or sticky EGR valves can cause idle problems as well as cruise surging. High NOx levels from an emission test could indicate a plugged/stuck or otherwise failed EGR system.

The simplest way to hook up the EGR system is to connect from a ported or EGR vacuum source on the carb to a blue 128° vacuum control valve (Motorcraft CX-1368). Then connect from the valve to the EGR valve itself. This will prevent the EGR from functioning till the vehicle is above 128° coolant temp.

Most stock carbs are jetted so the cruise circuit is lean to account for the reduced amount of combustible air. Eliminating the EGR will cause drivability issues. Aftermarket carbs are likely too rich and can be leaned out for an 8-10% increase in economy with EGR functioning. Emissions testing requires the system to be functional.

DISTRIBUTOR

Connect from ported vacuum to the distributor directly.

Alternatively a Red 225° 3-port VCV (Motorcraft DY-165A) can be used to protect against overheating at idle. There is no vacuum signal on a ported source at idle therefor no vacuum advance. By connecting the distributor to the center of the 3-port valve, the top port to ported vacuum and the bottom port to manifold vacuum when the coolant exceeds 225° vacuum will advance the timing causing the idle speed to increase which will cause the water pump and fan to increase. To my knowledge this wasn't used on the Bullnose trucks but did show up on some 70's vehicles. It could be useful for trucks that spend a lot of time idling.


CANISTER PURGE

The charcoal in the canister does not absorb hydrocarbons but instead holds them like a magnet. In it's most simple form it connects to the fuel tank vent line and to the intake through a purge valve that opens at cruise to pull the hydrocarbons off the charcoal into the engine to be burned. There is no performance benefit to removal but some aesthetic improvement. Most engines have carburetor bowl vents if the factory carbs are there.

Simplified hookup for aftermarket carbs without bowl vents. The center port of the canister purge valve is Tee'd into the EGR circuit between the VCV and EGR valve. This causes the purge to operate only at cruise when the engine is above 128°. The outer ports connect the canister to a suitable sized manifold vacuum port. The fuel vent line connects directly to the canister with no valves between.

I will edit this later and add the hookup for the carb bowl vents.


INTAKE/EXHAUST HEAT VALVES

...

AIR CLEANER DIVERTER VALVE

...

VACUUM ACTUATED THROTTLE KICKER
including A/C solenoid hookup
...

THERMACTOR (AIR) SYSTEM

...

DIAGRAMS

...

COLOR CODES

Red = Main vacuum
Green = EGR function
Orange = Heat control Valve (exhaust & intake) (AKA heat riser but more complex)
Yellow = Distributor advance
White = EGR vacuum (source)
Black = Mainly used for the Evaporative emissions control, also used for Thermactor ACV or diverter valve
Blue = Throttle Kicker control
Pink = Thermactor Air Bypass Valve (BPV)


COMMON ACRONYMS

A/CL DV - Air Cleaner Diverter Valve
A/CL BI MET - Air Cleaner BiMetallic valve
A/CL CWM: Air Cleaner Cold Weather Modulator
ACV - Air Control Valve
ACT - not sure, but on EFIs it means Air Charge Temperature sensor
ALT - Altitude compensation
AIR BPV - Air ByPass Valve (aka Thermactor Air Bypass = TAB)
BV - Bowl Vent
CARB: Carburetor
CPRV: Canister Purge Valve
EXH HCV - Exhaust Heat Control Valve
FLTR - Filter
HEAT VLV INT - Heat Valve Intake
HICV - Hot Idle Control Valve
IVV - Thermactor Idle Vacuum Valve
LCV - EGR Load Control Valve
MAN VAC - Manifold Vacuum
PCV - Positive Crankcase Ventilation
S - Spark port
SV CBV - Solenoid Valve Carborator Bowl Vent
TK - Throttle Kicker
TVV - Thermal Vacuum Valve
TVS - Throttle Valve Solenoid (aka SolePot, Dashpot)
VDV - Vacuum Diverter Valve
VCV - Vacuum Control Valve
VCKV: Vacuum Check Valve
VRDV - Distributor Vacuum Retard Delay Valve
VRESER: Vacuum Reservoir Solenoid Valve
PURGE CV: Vapor Canister Purge Valve
P/D MTR - Choke Pull Down


TRANSMISSION

The C6 vacuum modulator is connected to any source of manifold vacuum, commonly from a rear manifold vacuum tree.

Manual and AOD transmissions don't use vacuum.






***Note: I will add more when I have time. I am weak on the Thermactor system so if anyone has any info they'd like to share please post it. I also need some help/discussion on the air cleaner diverter valve. I believe it just goes through a heat sensitive bi-metallic valve on the air cleaner itself but I also believe it could be controlled in other ways through the use of coolant operated vacuum control valves. So a discussion there would be nice.

If anyone wants to add any common diagnostics, drivability symptoms, common fixes, etc for each system that would be great.

Lastly, corrections are very welcome... I've studied this a lot, but I don't claim to know it all perfectly

And finally, I don't claim this to be all my work, it's just a collection of what I've found and my interpretation of it.

 

Your intentions are noble, but I don't know if I agree with your definitions and theory of operation of the EGR below;

The egr system is frequently disabled for no cause. It has no impact on performance and in stock form is responsible for increased mileage. The system replaces some of the combustible air with an inert gas from the exhaust. This allows the engine to operate as if it were a smaller displacement than it really is and use less fuel.


From what I understand, it's main purpose is emssions and to decrease the NOx emissions of the engine by cooling the combustion process. Of course I don't have any reliable source right now except memory, so I am really in the same boat as you are, a theory with nothing to back it up.

Maybe we can create a sticky if we get it all worked out.

 

That's my hope.

I wasn't speaking to the the design parameters, but more to why you'd want to fix it and use it. The main designed function of EGR is emissions to reduce NOx from what I remember. A side benefit is an 8-10% increase in economy - at least in theory. Since many of these trucks are emissions exempt in practice I feel many people will simply delete what they don't understand. EGR is one that provided you have the equipment - i.e. you haven't swapped manifolds, it's better to hook it up and use it. You get better economy and we get cleaner air.

 

Please do me a favor and include the proper location for the vacuum line from the transmission (modulator of some sort I think I heard?) Mine's not hooked up and I need to know where to run it!

Well you hit the nail on the head when it comes to me anyway. Seems to me it's just "one less thing to break" when it's disabled.

 

David - I would rep you if I could. That's a good cause and a good start toward it.

 

Hook the trans to any source for manifold vacuum.

As for "one less thing to break"... Take the bus, then you don't have to worry about anything on your truck breaking...

If you remove the EGR you must retune your carb. Yeah, I know, many will say they didn't but you can cause drivability issues and damage. I'm assuming that the people who are going to read this want their truck to run it's best...

 

Awesome thread idea! I'll be following this one closely as my trucks biggest issue is vacuum line issues lol.

 

!!!! THANKS !!!!!
I was looking at my emissions sticker yesterday trying to decipher the acronyms but didn't have time to wade through the manual last night. You've saved me a lot of time.
As I work on my carb swap if I come across anything to add, I will.

 

I got him for you!

 

Thanks!! Appreciate it.

 

I still don't agree with the economy theory yet. In my experience without the EGR working, and the carb tuned properly, you can actually lift your foot up off the gas pedal a little bit, and still keep the same road speed.

Correct me if I am wrong, but I don't think you will ever find a NASCAR team using a EGR system. If they could keep the power up, and get better fuel economy at the same time using a EGR system, I am sure they would do it. They win races all the time with fuel economy.

I do agree, if you have a completely stock engine, with stock emissions, and you just disconnect the EGR, you can have problems. What I am saying is if you wipe the slate clean, and with a different carb and different tune on the engine, if you leave out the EGR, you can see some gains, but putting out more NOx while doing it.

 

The EGR reduces combustion temps by displacing some of the oxygen of the incoming charge.
This allows very lean mixtures at cruise without knock or overheating.

If you're racing, you are never cruising

I go the Rep denied too, but appreciate all the effort you have put into this post.