Emissions Systems And Components

[Scaramoche]

I have spent the day trying to teach myself the emission systems for my 89 pathfinder. In doing so I began documenting it, and figure I would share what I have found. One system I'm still having difficulty understanding(because of lack of documentation, and diagrams) is the AIV system, so if somone can explain it I would greatly appreciate it. Also over the next few days...weeks, im fixing my emissions, and will take pics, to aply to this right up. Also if I got something wrong, please let me know, cause this is the first time ive ever tackled emissions.

 

Thanks

Scara

 

 

PCV system

 

The pcv system(positive crankcase ventilation) was created to decrease sludge, and unburned hydrocarbons. This system is based of the fact that when the engine is running a small amount of gas escapes the piston rings and gets pumped into the crankcase. The pcv systems purpose is take these gas's and pump them back into the combustion chamber.

 

How it works.

 

From the Air cleaner/filter assembly clean air is directed into the valve covers.

 

From here it enters the crankcase where the air combines with the gas's in the crankcase.

 

Once the gas's are combined, they exit on the alternate valve cover.

 

From this valve cover, the gas is directed to the PCV valve which is connected to the intake manifold, to be combusted.

 

NOTE: at low speeds, the valve is partially open, as speed increases, so does the opening of the valve.

 

NOTE:if PCV is closed, broken etc, it can cause oil leaks at gaskets, oil pan, etc.

 

 

Evaporative Emission Control system

 

The purpose of this system is to resolve the problem caused by escaping gas(from tank) fumes. The parts involved are the GAS TANK, VAPOR/LIQUID SEPARATOR(ALSO KNOWN AS FUEL CHECK VALVE), VAPOR VENT LINE, CABON CANISTER, VACUUM SIGNAL LINE, AND CANISTER PURGE LINE.

 

How it works.

 

From the gas tank a vent line runs to the FUEL CHECK VALVE.

 

The FUEL CHECK VALVE has 2 inputs. The fuel tank runs one end of the valve, while the other connects to the carbon canister side. Inside the valve, liquid gas funnels back down the input of the fuel tank, while the vapors continue on to the canister.

 

Once the vapor has left the fuel check valve, it goes to the charcoal canister.

 

While stopped or at idle, the canister holds the captured vapors. Then as rpm(throttle) increases, this causes a vacuum which opens the purge control valve, cleaning out trapped vapors.

 

These Vapors coming from the purge valve, go directly to the intake manifold, to be burned.

 

NOTE: the canister has 3 lines.

1-vapors coming from the Fuel check valve

2-Vacuum line that connects to the throttle body(top connector)

3-purge line, which goes to the intake manifold.(bottom connector)

 

NOTE: to test the Fuel check valve

1-blow through gas input, you should have a lot of resistance.

2-blow through the canister side, you should have no resistance.

 

 

Automatic temperature controlled(ATC) air cleaner.

 

This system deals with how temperature effects air/fuel mixture, and ultimately the atomization of fuel. For example when the intake air is cold, as well as the engine has a more difficult time atomizing. The result is more hydrocarbons in the exhaust. So this system basically does the following, when the engine is cold, it causes hot air to be drawn in, when the vehicle reaches operating temperature, it draws cool air.

 

 

How it works.

 

Inside the air cleaner there is the ATC temp sensor. When the vehicle is “cold”, it causes a vacuum, as it heats up there is less vacuum.

 

From the ATC sensor a vacuum line runs to the ATC vacuum motor.

 

The ATC opens or closes(ie directing cold or hot air) altering the intake air locations.

 

The 2 air intake locations are from the manifold(there is a shroud where the snorkel connects), or from outside the vehicle.

 

 

 

 

Exhaust Gas Recirculation(EGR) system.

 

The purpose of this system is to take exhaust gas's from the engine and direct them back into the combustion chamber.

 

How it works.

 

Behind your intake manifold, is the EGR valve. This valve is bolted to the intake manifold. It has 2 connections.

1-connection one is from your exhaust(it's the big connection)

2-is a vacuum line connection, that is on top of EGR.

 

When there is no vacuum pressure applied to the EGR, the recirculated gas IN NOT entering the intake manifold.

 

From the EGR Valve vacuum line, you connect to the Thermal Vacuum Valve(TVV). This valves function is to keep the vacuum off, until the engine is at a temp of 134-145 F. At which point it opens allowing the EGR control solenoid to apply a vacuum. There are 2 connections to this device.

1-vacuum line from EGR Control Valve

2-Vacuum line from EGR Control Solenoid

 

The EGR Control solenoid has 3 visible connections.

1-Vacuum line from TVV(and ultimately EGR Valve)

2-Vacuum line that connects to the air cleaner.

3-Wiring harness that controls open/closing of the EGR control Solenoid.

 

 

Air induction Valve(AIV) system.

 

The purpose of this system is to allow air into the exhaust. When these hot exhaust gas's are introduced to Air(oxygen), additional “burning” of the exhaust gas's will occur, reducing your emissions. What makes this system seem complex is what occurs in the air induction valve.

 

NOTE: The air induction valve(round clam/shell looking device). While it seems relatively easy to “Push” air into the exhaust, but because of physics, there is a chance you can get “blowback”, ie exhaust gas's not going out your tailpipe, but rather exiting at the AIV. So the AIV has 2 reed valves to prevent this.

 

 

That all I can figure out on AIV so far

[frecklecolouredbrain]

There are to parts to the AIV. There is the air box, and the control box. The control box has vacuum operated valve connected to a vaccuum solenoid that is controled by a relay; all behind the airbox.

 

The system operates via the EAV tube connected to the exhaust manifold. Between each puff of exhaust, there is a tiny vacuum that allows the outside air pressure to enter through the reeds in the airbox, and down to the cataytic convertor. during normal operation, the control box remains in the open position to allow air to freely pass. At higher rpm, there is not enough time between exhaust puffs to suck in enough air, so the vacuum solenoid closes the control box until enough vacuum is produced. the control box then opens, allowing air to pass in for a few seconds before closing again. There is no sensor for this; the ECCS controls it based on time and a physics equation.

 

I studied the system pretty closely before I ripped it out.

[Scaramoche]

There are to parts to the AIV. There is the air box, and the control box. The control box has vacuum operated valve connected to a vaccuum solenoid that is controled by a relay; all behind the airbox.

 

The system operates via the EAV tube connected to the exhaust manifold. Between each puff of exhaust, there is a tiny vacuum that allows the outside air pressure to enter through the reeds in the airbox, and down to the cataytic convertor. during normal operation, the control box remains in the open position to allow air to freely pass. At higher rpm, there is not enough time between exhaust puffs to suck in enough air, so the vacuum solenoid closes the control box until enough vacuum is produced. the control box then opens, allowing air to pass in for a few seconds before closing again. There is no sensor for this; the ECCS controls it based on time and a physics equation.

 

I studied the system pretty closely before I ripped it out.

 

Thanks that helps alot...my big issue not is where the vaccum lines connect. seems this is whats causing me to fail emissions. im golden on everything, except low HC's im supposed to be at like 200, im at 3000, not even playing in the same ballpark. I know something is completly fudged, persise1 or kingman said it's because of this...sigh, i need to fix

[frecklecolouredbrain]

the air fiter in the AIV airr box is probably plugged. = no fresh air to cat.

Edited May 28, 2010 by LittleReD89

[Scaramoche]

the air fiter in the AIV airr box is probably plugged. = no fresh air to cat.

 

 

I completely took apart the air box, and cleaned, and verified it works(it is rusted like mad.) but it seems to be working, my "gas smell" has come down a bit, but now i think my cat is bad.

[putawaywet]

Im not much of a mechanic (although Im getting alot of experience).

Just had a new exhaust installed on my 89 Pathfinder (cat and all). I had removed the AIV valve not long before and a previous owner had removed the AIV air cleaner. The AIV was decentegrated. When they test ran it the cat got real hot and they were concerned it would burn up. Went to San Marcos Nissan and ordered a new AIV (also called a PAIR valve), air cleaner box, hoses and solenoid. I dont have emissions testing in my county yet but could pass now.

It made a noticable difference. Idles lower and seems to run a tad more smoothly.

 

Just for what its worth.