Work in progress. This article will explain the mysterious FSJ vacuum systems and emissions systems.
For details on vacuum routing and how each subsystem is plumbed, take a look at this article on vacuum routing.
Ever pop the hood on your FSJ and jump back in terror when you see all that black spaghetti? EGRs, TACs, AIR, CTOs, NLVRs, what the heck is all this junk, and why do you care? You've heard it before, rip out all that emissions gear that robs performance. Find out the truth, take control, and make your emissions gear work for you. Read on...
"Knowledge is an antidote to fear." -- Ralph Waldo Emerson (1803-1882)
Back when I was but a teen, I was fiddling around with my 1976 Buick Regal and wiggled a hose and broke a strange piece of plastic that cost more than $50 for the mechanic to replace. After that lesson, I didn't touch a piece of the vacuum system on any car for 10 years...
When I did, I was pretty pissed about all this strange gear so I decided to learn it and learn it well. I thought I'd share a little of that information with you so you can stop being ruled by your emissions equipment and make it work for you.
It all starts with the gasoline-powered, spark-fired, internal combustion engine. This motor as we all know, uses a throttle to control power by modulating the amount of air-fuel mixture entering the combustion chambers. When the piston moves downwards in the bore on the intake stroke, it is sucking air-fuel through the intake valve(s) by creating a drop in pressure inside the combustion chamber compared to the manifold. Vacuum is nothing more than air at a lower pressure than normal outside air.
Probably everyone has seen a tire or basketball deflate either quickly or over time. Differences in gas pressure want to equalize if you give them a chance to. A tire with a hole gives the air inside a chance to equalize to the pressure of the air outside. Likewise, the pressure drop inside the cylinder equalizes with the manifold pressure when the intake valve is open. Then the pressure in the intake manifold wants to equalize with the pressure in open air. Opening the throttle allows air to enter the intake manifold to try and equalize the pressure.
You can think of all this another way. Vacuum (suckiness) is generated in the cylinder, is passed on through the open intake valve to the manifold and then to the outside air through the throttle plate.
But the throttle plate isn't always wide open. When that happens, just as with that slow leak in a basketball, the air flows slowly from high pressure to low pressure. With pistons always moving, and the throttle nearly closed, the pressure drop inside the manifold is maintained relative to the outside air. That is to say, there is vacuum in the manifold. When you open the throttle fully, all the vacuum generated by the engine is transmitted to the outside air, meaning there is vacuum detectable at a point above the throttle plates.
At idle, with throttle plates almost totally closed, the engine is trying to draw air through a tiny opening, generating vacuum in the area of the manifold below the throttle plates. As the throttle plates open more and more, the amount of vacuum in the manifold goes lower and lower. The amount of manifold vacuum acts as an indicator of engine load. More vacuum, less engine load. To use that indicator, carburetors have a hole in one of the bores just below where the throttle plates are located at idle. That hole is connected to a passage that ultimately leads to a nipple on the exterior of the carburetor. Hook vacuum hose up to the nipple and run it to any vacuum operated device: spark advance, AIR system, etc.
Ported vacuum is similar to manifold vacuum. A hole in the carburetor bore is located just above where the throttle plates sit at idle. So at idle, ported vacuum is zero. But just off idle, ported vacuum and manifold vacuum share the same location with respect to the throttle plates. So they have the same signal.
These two signals are exploited in the design of the emissions and vacuum system on your Full Size Jeep. Vacuum is used to turn devices on or off, control valves, and modulate transmission shift points, all based on engine load.
The EGR cannot be engaged during idle without degrading idle significantly, but it has to be engaged during part throttle load, so ported vacuum is used. Vacuum advance is a can of worms but suffice it to say that the engineering intent (for better or worse) was for the FSJ timing to be retarded at idle but advance off-idle and decrease with increasing engine load and increasingly rich mixture. The AIR system is operated by manifold vacuum.
Delay valves "leak" in one direction. When vacuum is applied to one side (the vacuum signal), vacuum slowly increases on the other side until it matches the "signal" amount of vacuum. Say 15 in-Hg is applied on one side of a delay valve. The other side will climb until it reaches 15 in-Hg. The time it takes to do this depends on the valve and several vacuum delay valves are typically available. A table of the various delays are listed on Wikipedia. Delay valves are found inline attached to the EGR and other devices to smooth the transition of the device from off to on (or vice versa). Reverse delay valves prevent vacuum from leaking; they're basically check valves. You can find these inline to such devices as the AIR system valve.
The purpose of the CTO is simple: it selects a vacuum source based on coolant temperature. The device typically has 3 ports. The middle port is the "output" port. One port is active below the temperature threshold of the CTO, the other is active above the threshold.
A Thermal Vacuum Switch (TVS) has two ports and allows vacuum to pass between the ports above a certain temperature.
So what is a "Non-Linear Vacuum Regulator"? The simple answer is that it limits the amount of vacuum advance delivered to the distributor when the engine is cold. These appeared only on late model FSJs. It has three ports and takes manifold and ported vacuum as inputs and delivers this to the output port.
A vacuum reservoir is simply a container with a moderately large volume enabling it to "store" vacuum that powers accessories. It is usually hooked to manifold vacuum because this vacuum is present more often during vehicle operation. It has a check valve to prevent vacuum leaking back into the manifold.
It is usually used in conjunction with devices that may require vacuum to operate at any point during the vehicle's operation. For example, the Emergency-drive on your Borg-Warner QuadraTrac FSJ, the heater controls, the cruise control, or the mode (2wd/4wd) selector on your SelecTrac (NP228/NP229) FSJ. An 80's FSJ will have a black vacuum reservoir on the driver fender under the hood which resembles a coffee can, and another reservoir that looks like a black softball on the firewall which operates the SelecTrac and Heater controls.
The brake boosters in FSJs and many other cars are operated by vacuum power. Vacuum operates on a large diaphragm (sometimes two) in the brake booster, the giant round thing on which the master cylinder mounts. The engine needs to be producing enough vacuum during cruise and idle to operate the booster. A check valve holds vacuum in the booster so you have brake boost for a few applications after the motor is turned off.
in progress
General Motors' Turbo-Hydramatic automatic transmissions modulate shift points and internal line pressures based on engine vacuum. Full Size Jeeps from the 60's through 1979 used a TH400 transmission with a vacuum modulator hooked to manifold vacuum that essentially acts like a throttle position sensor or, more correctly, an engine load sensor. Light throttle means high vacuum, early shifts, and low line pressures inside the transmission. Heavy throttle means low vacuum, late shifts, and higher pressures.
in progress
Quite a bit of debate exists about using manifold vs ported vacuum for spark advance. You can do additional research on this. Ported vacuum is the factory design. However, when idling or cruising, the fuel mixture is lean and lean AF mixtures need more time to burn so more advance is optimal, not less. Manifold vacuum would deliver maximum advance at idle and very low speed cruise. Higher speed cruise (say above 50mph) seems to require quite a bit of throttle input on most FSJs so ported and manifold probably have the same amount of vacuum at this point.
The charcoal vapor canister is designed to prevent venting of raw fuel vapors to the atmosphere. Gas tank and fuel bowl vent lines connect to the inlets of the canister. The carb bowl vents to the canister through an electrical valve that is opened when the vehicle is off and closed when it is running.
The vapors are recovered by drawing air through the canister and into the intake manifold. The FSJ uses a 2-stage purge system. A purge valve sits on top of the canister and is activated by a ported vacuum signal.
At idle, the purge port is closed by the purge valve but a small amount of vapor is drawn into the PCV and intake manifold through the vapor separator, a 3-nipple device that looks like a fuel filter. It's actually a metering device.
At off-idle, moderate engine loads, a ported vacuum signal opens the purge valve allowing the PCV to draw a greater amount of vapor into the intake through the purge port on the vapor canister.
The AIR system injects fresh air into the exhaust system, either at the exhaust manifolds or into the Catalytic Converter. Some think this simply dilutes the pollutants. Instead, the addition of air (and oxygen) to essentially burn unburned and partially burned fuel through oxidation. Under heavy acceleration when the motor is running rich, air injection is diverted to the catalytic converter (on vehicles so equipped) to aid in catalytic conversion of unburned fuel and carbon monoxide. More details on Wikipedia.
When the vehicle is under load (towing or climbing a hill) and operating at part throttle, combustion temperatures can climb high, resulting in the formation of Oxides of Nitrogen (NOx) and may also cause spark knock or detonation. The Exhaust Gas Recirculation system aims to prevent both by injecting a small amount of exhaust gas into the intake stream under part throttle load conditions.
The EGR valve diverts exhuast gas from one area of the intake manifold to the other. The intake manifold is designed with exhaust passageways to heat the air-fuel mixture to improve cold weather driving and AF atomization. This stream is directed into the passages leading to cylinder head intake valves by the EGR valve. It is activated by, typically, a specially tuned ported vacuum source on the carburetor through a Thermal Vacuum Switch and/or a CTO, as well as an optional delay valve.
Other options to reduce NOx are increased AF mixture (increasing CO and HC pollution) or retarding timing (reducing efficiency and performance). Instead, with EGR, you can run a more aggressive timing curve, so in a way EGR is actually a performance enhancer. More details on the topic of EGR can be found here.
One of the very first emissions-related systems is the Positive Crankcase Venitlation system, which addresses the unavoidable fact of blowby, where small amounts of exhaust, fuel and air leak by the piston rings of a motor. Prior to PCV, the crankcase was ventilated directly to the atmosphere (on Chevys you have seen the crankcase vent on the valve covers). PCV is designed to use engine vacuum to suck the partially unburned gasses out of the crankcase and into the intake. The system consists of a PCV Filter, and a PCV Vent.
This one is simple. The goal is to present uniform temperature air to your engine. The system is comprised of an air cleaner housing with a snorkel, a flexible tube (on the 80+ rigs) to the core support (cool air), a flexible aluminum tube that connects to the bottom of the snorkel and to the exhaust manifold (the hot air), a temp sensor, delay valves, and a valve to proportion the amount of cool and hot air going to the engine. A vacuum motor with a delay valve attached controls the valve on the snorkel. Actually there are two valves. The other one shuts off air to the engine to prevent run-on and is also controlled by a vacuum motor, a delay valve, and gets its vacuum from the same source.
I have the vac advance runing off the variable pressure side of the
carb as well as the egr valve behind the carb and the air control valve.
I run one CTO which controls whether the distributor gets manifold vac or ported vac. My setup is a little more complex but just hooking manifold and ported to a CTO and sending the output to the dist is perfectly fine.
Run the EGR off of ported vac but switch it thru the oem thermal vacuum switch.
There are no pressure specs for really anything. The devices don't care and there are no regulators. That said, your engine should read at least 12"-17" of Hg manifold vacuum at idle at this altitude. The real question is whether you are running ported or manifold vacuum to various components.
The AIR system has a unit with two valves (on 86+ FSJs; one on 85-) bolted on a long steel rod to the P/S pump with big AIR hoses attached. They should hook to manifold vacuum. One valve (the one on top I think) switches it on and is supposed to source from manifold vacuum thru a CTO (on only when warm). The other chooses to divert air to manifold or catalytic converter (bottom valve). The one that switches on/off should go thru a reverse delay valve (basically holds constant vacuum on the device).
Your manifold vacuum should not go to the charcoal canister, only. The valve on that device is a dump valve that empties gas vapor contents into the intake. So IIRC, it should hook to ported vacuum to dump only under acceleration/load.
One other tip, don't use bolts/screws to plug vacuum hoses. They leak through the threads (I've tested this with a vacuum pump). What I know works perfectly is a steel rod or the plastic vacuum caps you can get from parts stores. Too many leaks and you have problems running too lean, stalling out, etc.
For details on vacuum routing and how each subsystem is plumbed, take a look at this article on vacuum routing.
1.0 Introduction
Ever pop the hood on your FSJ and jump back in terror when you see all that black spaghetti? EGRs, TACs, AIR, CTOs, NLVRs, what the heck is all this junk, and why do you care? You've heard it before, rip out all that emissions gear that robs performance. Find out the truth, take control, and make your emissions gear work for you. Read on...
"Knowledge is an antidote to fear." -- Ralph Waldo Emerson (1803-1882)
Back when I was but a teen, I was fiddling around with my 1976 Buick Regal and wiggled a hose and broke a strange piece of plastic that cost more than $50 for the mechanic to replace. After that lesson, I didn't touch a piece of the vacuum system on any car for 10 years...
When I did, I was pretty pissed about all this strange gear so I decided to learn it and learn it well. I thought I'd share a little of that information with you so you can stop being ruled by your emissions equipment and make it work for you.
2.0 Vacuum
Vacuum Basics
It all starts with the gasoline-powered, spark-fired, internal combustion engine. This motor as we all know, uses a throttle to control power by modulating the amount of air-fuel mixture entering the combustion chambers. When the piston moves downwards in the bore on the intake stroke, it is sucking air-fuel through the intake valve(s) by creating a drop in pressure inside the combustion chamber compared to the manifold. Vacuum is nothing more than air at a lower pressure than normal outside air.
Probably everyone has seen a tire or basketball deflate either quickly or over time. Differences in gas pressure want to equalize if you give them a chance to. A tire with a hole gives the air inside a chance to equalize to the pressure of the air outside. Likewise, the pressure drop inside the cylinder equalizes with the manifold pressure when the intake valve is open. Then the pressure in the intake manifold wants to equalize with the pressure in open air. Opening the throttle allows air to enter the intake manifold to try and equalize the pressure.
You can think of all this another way. Vacuum (suckiness) is generated in the cylinder, is passed on through the open intake valve to the manifold and then to the outside air through the throttle plate.
But the throttle plate isn't always wide open. When that happens, just as with that slow leak in a basketball, the air flows slowly from high pressure to low pressure. With pistons always moving, and the throttle nearly closed, the pressure drop inside the manifold is maintained relative to the outside air. That is to say, there is vacuum in the manifold. When you open the throttle fully, all the vacuum generated by the engine is transmitted to the outside air, meaning there is vacuum detectable at a point above the throttle plates.
Ported and Manifold Vacuum
At idle, with throttle plates almost totally closed, the engine is trying to draw air through a tiny opening, generating vacuum in the area of the manifold below the throttle plates. As the throttle plates open more and more, the amount of vacuum in the manifold goes lower and lower. The amount of manifold vacuum acts as an indicator of engine load. More vacuum, less engine load. To use that indicator, carburetors have a hole in one of the bores just below where the throttle plates are located at idle. That hole is connected to a passage that ultimately leads to a nipple on the exterior of the carburetor. Hook vacuum hose up to the nipple and run it to any vacuum operated device: spark advance, AIR system, etc.
Ported vacuum is similar to manifold vacuum. A hole in the carburetor bore is located just above where the throttle plates sit at idle. So at idle, ported vacuum is zero. But just off idle, ported vacuum and manifold vacuum share the same location with respect to the throttle plates. So they have the same signal.
These two signals are exploited in the design of the emissions and vacuum system on your Full Size Jeep. Vacuum is used to turn devices on or off, control valves, and modulate transmission shift points, all based on engine load.
The EGR cannot be engaged during idle without degrading idle significantly, but it has to be engaged during part throttle load, so ported vacuum is used. Vacuum advance is a can of worms but suffice it to say that the engineering intent (for better or worse) was for the FSJ timing to be retarded at idle but advance off-idle and decrease with increasing engine load and increasingly rich mixture. The AIR system is operated by manifold vacuum.
3.0 The Building Blocks
Delay Valves and Reverse Delay Valves
Delay valves "leak" in one direction. When vacuum is applied to one side (the vacuum signal), vacuum slowly increases on the other side until it matches the "signal" amount of vacuum. Say 15 in-Hg is applied on one side of a delay valve. The other side will climb until it reaches 15 in-Hg. The time it takes to do this depends on the valve and several vacuum delay valves are typically available. A table of the various delays are listed on Wikipedia. Delay valves are found inline attached to the EGR and other devices to smooth the transition of the device from off to on (or vice versa). Reverse delay valves prevent vacuum from leaking; they're basically check valves. You can find these inline to such devices as the AIR system valve.
Coolant Temperature Override (CTO)
The purpose of the CTO is simple: it selects a vacuum source based on coolant temperature. The device typically has 3 ports. The middle port is the "output" port. One port is active below the temperature threshold of the CTO, the other is active above the threshold.
Thermal Vacuum Switch (TVS)
A Thermal Vacuum Switch (TVS) has two ports and allows vacuum to pass between the ports above a certain temperature.
Non-Linear Vacuum Regulator (NLVR)
So what is a "Non-Linear Vacuum Regulator"? The simple answer is that it limits the amount of vacuum advance delivered to the distributor when the engine is cold. These appeared only on late model FSJs. It has three ports and takes manifold and ported vacuum as inputs and delivers this to the output port.
Vacuum Reservoir
A vacuum reservoir is simply a container with a moderately large volume enabling it to "store" vacuum that powers accessories. It is usually hooked to manifold vacuum because this vacuum is present more often during vehicle operation. It has a check valve to prevent vacuum leaking back into the manifold.
It is usually used in conjunction with devices that may require vacuum to operate at any point during the vehicle's operation. For example, the Emergency-drive on your Borg-Warner QuadraTrac FSJ, the heater controls, the cruise control, or the mode (2wd/4wd) selector on your SelecTrac (NP228/NP229) FSJ. An 80's FSJ will have a black vacuum reservoir on the driver fender under the hood which resembles a coffee can, and another reservoir that looks like a black softball on the firewall which operates the SelecTrac and Heater controls.
4.0 Non-Emissions Components
Brake Booster
The brake boosters in FSJs and many other cars are operated by vacuum power. Vacuum operates on a large diaphragm (sometimes two) in the brake booster, the giant round thing on which the master cylinder mounts. The engine needs to be producing enough vacuum during cruise and idle to operate the booster. A check valve holds vacuum in the booster so you have brake boost for a few applications after the motor is turned off.
Cruise Control
in progress
Transmission Modulator
General Motors' Turbo-Hydramatic automatic transmissions modulate shift points and internal line pressures based on engine vacuum. Full Size Jeeps from the 60's through 1979 used a TH400 transmission with a vacuum modulator hooked to manifold vacuum that essentially acts like a throttle position sensor or, more correctly, an engine load sensor. Light throttle means high vacuum, early shifts, and low line pressures inside the transmission. Heavy throttle means low vacuum, late shifts, and higher pressures.
4-Wheel Drive Systems
in progress
Spark advance
Quite a bit of debate exists about using manifold vs ported vacuum for spark advance. You can do additional research on this. Ported vacuum is the factory design. However, when idling or cruising, the fuel mixture is lean and lean AF mixtures need more time to burn so more advance is optimal, not less. Manifold vacuum would deliver maximum advance at idle and very low speed cruise. Higher speed cruise (say above 50mph) seems to require quite a bit of throttle input on most FSJs so ported and manifold probably have the same amount of vacuum at this point.
5.0 Emissions Components
Charcoal Vapor Canister
The charcoal vapor canister is designed to prevent venting of raw fuel vapors to the atmosphere. Gas tank and fuel bowl vent lines connect to the inlets of the canister. The carb bowl vents to the canister through an electrical valve that is opened when the vehicle is off and closed when it is running.
The vapors are recovered by drawing air through the canister and into the intake manifold. The FSJ uses a 2-stage purge system. A purge valve sits on top of the canister and is activated by a ported vacuum signal.
At idle, the purge port is closed by the purge valve but a small amount of vapor is drawn into the PCV and intake manifold through the vapor separator, a 3-nipple device that looks like a fuel filter. It's actually a metering device.
At off-idle, moderate engine loads, a ported vacuum signal opens the purge valve allowing the PCV to draw a greater amount of vapor into the intake through the purge port on the vapor canister.
AIR (Air Injection Reactor) System
The AIR system injects fresh air into the exhaust system, either at the exhaust manifolds or into the Catalytic Converter. Some think this simply dilutes the pollutants. Instead, the addition of air (and oxygen) to essentially burn unburned and partially burned fuel through oxidation. Under heavy acceleration when the motor is running rich, air injection is diverted to the catalytic converter (on vehicles so equipped) to aid in catalytic conversion of unburned fuel and carbon monoxide. More details on Wikipedia.
Exhaust Gas Recirculation (EGR)
When the vehicle is under load (towing or climbing a hill) and operating at part throttle, combustion temperatures can climb high, resulting in the formation of Oxides of Nitrogen (NOx) and may also cause spark knock or detonation. The Exhaust Gas Recirculation system aims to prevent both by injecting a small amount of exhaust gas into the intake stream under part throttle load conditions.
The EGR valve diverts exhuast gas from one area of the intake manifold to the other. The intake manifold is designed with exhaust passageways to heat the air-fuel mixture to improve cold weather driving and AF atomization. This stream is directed into the passages leading to cylinder head intake valves by the EGR valve. It is activated by, typically, a specially tuned ported vacuum source on the carburetor through a Thermal Vacuum Switch and/or a CTO, as well as an optional delay valve.
Other options to reduce NOx are increased AF mixture (increasing CO and HC pollution) or retarding timing (reducing efficiency and performance). Instead, with EGR, you can run a more aggressive timing curve, so in a way EGR is actually a performance enhancer. More details on the topic of EGR can be found here.
Positive Crankcase Ventilation (PCV)
One of the very first emissions-related systems is the Positive Crankcase Venitlation system, which addresses the unavoidable fact of blowby, where small amounts of exhaust, fuel and air leak by the piston rings of a motor. Prior to PCV, the crankcase was ventilated directly to the atmosphere (on Chevys you have seen the crankcase vent on the valve covers). PCV is designed to use engine vacuum to suck the partially unburned gasses out of the crankcase and into the intake. The system consists of a PCV Filter, and a PCV Vent.
Thermal Air Control (TAC)
This one is simple. The goal is to present uniform temperature air to your engine. The system is comprised of an air cleaner housing with a snorkel, a flexible tube (on the 80+ rigs) to the core support (cool air), a flexible aluminum tube that connects to the bottom of the snorkel and to the exhaust manifold (the hot air), a temp sensor, delay valves, and a valve to proportion the amount of cool and hot air going to the engine. A vacuum motor with a delay valve attached controls the valve on the snorkel. Actually there are two valves. The other one shuts off air to the engine to prevent run-on and is also controlled by a vacuum motor, a delay valve, and gets its vacuum from the same source.
My Configuration
I have the vac advance runing off the variable pressure side of the
carb as well as the egr valve behind the carb and the air control valve.
I run one CTO which controls whether the distributor gets manifold vac or ported vac. My setup is a little more complex but just hooking manifold and ported to a CTO and sending the output to the dist is perfectly fine.
Run the EGR off of ported vac but switch it thru the oem thermal vacuum switch.
There are no pressure specs for really anything. The devices don't care and there are no regulators. That said, your engine should read at least 12"-17" of Hg manifold vacuum at idle at this altitude. The real question is whether you are running ported or manifold vacuum to various components.
The AIR system has a unit with two valves (on 86+ FSJs; one on 85-) bolted on a long steel rod to the P/S pump with big AIR hoses attached. They should hook to manifold vacuum. One valve (the one on top I think) switches it on and is supposed to source from manifold vacuum thru a CTO (on only when warm). The other chooses to divert air to manifold or catalytic converter (bottom valve). The one that switches on/off should go thru a reverse delay valve (basically holds constant vacuum on the device).
Your manifold vacuum should not go to the charcoal canister, only. The valve on that device is a dump valve that empties gas vapor contents into the intake. So IIRC, it should hook to ported vacuum to dump only under acceleration/load.
One other tip, don't use bolts/screws to plug vacuum hoses. They leak through the threads (I've tested this with a vacuum pump). What I know works perfectly is a steel rod or the plastic vacuum caps you can get from parts stores. Too many leaks and you have problems running too lean, stalling out, etc.
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