The Definitive 79-80 Desmog Guide (1 Viewer)

[Toyoland66]

This thread is the result of many hours of research and questions asked. I am using it to compile the final data for how to desmog a 79-80 FJ40 while still retaining beneficial systems. This is not intended to be a debate on the merits of desmogging your vehicle, those discussions exist elsewhere.

That being said, if any of the following looks inaccurate let me know and I will edit.

The following diagrams show the stock emissions system

79emission%20schematic

79emission%20schematic2

By desmogging we eliminate the following systems:
Air Injection (AI)
Exhaust gas recirculation (EGR)
Choke Opener (CO)

And we retain the following systems:
distributor advance
deceleration fuel cutoff (i.e. vac switch, fuel cutoff solenoid)
evap (i.e. fuel tank and carb bowl venting, charcoal canister)
choke breaker (CB)
hot air intake (HAI)
distributor cap vent
hot idle compensation (HIC)
positive crankcase ventilation (PCV)
-optional- High Altitude Control (HAC)

The following schematic shows the overall result w/o HAC, w/ HAC will be discussed later.

79emissionschematic - for Desmog - w-o HAC

The following posts will outline these systems individually.

 

[Toyoland66]

Reserved - Deleted Ai & EGR

I don't have any good pics for this as I did it a long time ago. You basically remove:

For AI:
Air pump
Associated Ducting/ tubing
Air rail (from head) and plug holes with either threaded plugs (Jim C sells or McMaster Carr) or Toyota part #90340-14001
Plug open holes in air cleaner with rubber caps (Jim C sells or McMaster Carr)

For EGR:
EGR Cooler (attaches to DS of engine block underneath exhaust manifold)
EGR piping to exhaust manifold & cap manifold where it attached
EGR valve and vacuum modulator

You need to modify the fitting that attaches to the DS of the intake manifold right below the carburetor. The pipe that attaches to the EGR valve needs to be cut off and sealed shut (I welded mine shut). You can see it in the photo, it is the fitting that is painted silver, you can see a rough spot where the EGR tube was welded shut. The remaining tube is the vac source for the PCV valve.

IMG_0794[1]

 

[Toyoland66]

Choke Opener

This is the only item attached to the carburetor that gets eliminated. If you look at the overall desmog schematic you will notice that in the final configuration the choke opener gets connected to atmosphere (air cleaner) rendering it inoperable. This is also the case in the Rich Adams/ Jim C's desmog schematic from the tech section.

The easiest method is to simply connect the CO to atmosphere:

79emissionschematic - Choke Opener

If you don't know what the CO looks like, it is the round gold thing with a nipple on the left side in the bottom right side of this photo:

IMG_0799[1]

It is on the firewall side of the carb as it sits in the vehicle.

Here is another view of it, in this photo it is on the bottom left:

IMG_0800[1]

If you are removing the carb for a rebuild the CO can be removed completely, however the bracket that it sits on needs to be retained as it also holds one of the linkage springs. The bracket can be removed from the carb and a cut made at the red line in the following photo:

Removal of CO

This is the modified bracket with the removed CO:

IMG_0844

Removing the CO also makes this piece of linkage obsolete (Circled in red)

Removal of CO Linkage

The bolt in the middle is removed, and the L shaped linkage and rod are also removed. The rod and where it attaches to the shaft are shown in the following photos:

IMG_0842

IMG_0843

Here is the final result with the CO bracket bolted back on to the carb.

IMG_0845

And the before photo for reference:

Removal of CO

 

[Toyoland66]

Advancer

The distributor advance connects to the advancer port on the base of the carb. Reference the first photo on the first post which labels these ports in the top right corner of the photo. This is one of the simpler circuits of the schematic.

79emissionschematic - Advancer

The only thing to be considered here is whether you connect to the nipple closer to the distributor (main advance, right side in the schematic) or the further nipple from the distributor (high altitude advance, left side in the schematic). The high altitude port will advance the distributor less and using this port may be required to eliminate pinging if you don't have a re-curved distributor. Experimentation may be required.

The following photo shows the connection to the carb (labeled 6):

IMG_0783[1]

And the connection to the high altitude advance port on the distributor (also labeled 6):

IMG_0782[1]

 

[Toyoland66]

Vac Switch

The vac switch cut fuel to the carb when decelerating and is controlled by the emissions computer. Sometimes this system does not work and the fix is to permanently ground the switch so that it opens when the ignition is on. A failure of this system will cut fuel from the carb and result in starvation. Search green wire mod for more info.

The following shows this circuit on the schematic, also a very simple circuit.

79emissionschematic - Vac Switch2

The fuel cut solenoid is screwed into the carburetor and is on the middle right of this photo with the wires coming out of it. It sits on the firewall side, valve cover side in the vehicle and is at the top of the carb:

IMG_0800[1]

Here is a closer up blurry photo of it:
IMG_0806[1]

The vac switch sits on the drivers side fender, it has a single nipple on it, not to be confused with the item that sits directly below it with two nipples 90 degrees apart. It is labeled 8 in this photo:

IMG_0787[1]

It connects to the fuel cut port on the base of the carburetor (reference first photo of first post). Shown here labeled 8:

IMG_0786[1]

 

[Toyoland66]

Evap

The evap system vents the gas tank and carb bowl and recycles any fuel vapors.

It works by using two vacuum switches. The BVSV is a thermo switch that is located in the thermostat housing. It allows vacuum to pass through it once the engine comes up to operating temperature. The VCV allows vacuum to pass through one side of it when the other side is under vacuum. In other words, once the vehicle comes up to temp the charcoal canister is exposed to manifold vacuum through the VCV.

Here is the schematic of how this circuit is routed:

79emissionschematic - Evap

The EGR port on the base of the carb (reference post 1 pic 1) is the vacuum source to "turn on" the VCV. Again, it is routed through the BVSV so it only "turns on" the VCV once the engine comes up to temp. Pic of the connection at the carb (labeled 7):

IMG_0784[1]

From here it goes to the BVSV which is located on the thermostat housing

IMG_0788[1]

there are 3 BVSV in the stock thermostat housing. Two on the lower drivers side, and one on the top. You only need one for the desmog configuration, ideally it should be the light blue BVSV but according to the experts it doesn't really matter, the different colors open at different operating temperatures.

From the BVSV the hose connects to the side port on the black side of the VSV, labeled 9:

IMG_0789[1]

This circuit is what opens/ closes the VSV. The other circuit of the evap system is what connects the charcoal canister to manifold vacuum when the VSV is open. The vaccum source is the large barb on the carb insulator. This is on the fender side of the carb, the right port in this photo:

IMG_0817[1]

The same connection labeled 11 in this photo - still in the vehicle:

IMG_0792[1]

This is connected to large nipple on the top of the VSV, shown here labeled 11

IMG_0791[1]

The connection to the charcoal canister is made through a metal tube that connects to the firewall and drivers side fender. This tube connects via hose to the larger nipple on the side of the VSV, shown here labeled 10:

IMG_0790[1]

The final connection of the circuit is from the small nipple on the side of the VSV to atmostphere (air cleaner) shown here labeled 3:

IMG_0770[1]

For reference here is a photo of the charcoal canister. The closest port connects to the gas tank, the middle port connects to the metal tube on the firewall (which goes to the VSV) and the furthest back port connects through the control valve to the carburetor bowl vent. Notice that this is a molded hose and is cracked, this part is still available from Toyota and I believe the part number is 77759-14011.

IMG_0793[1]

 

[Toyoland66]

Ported CB, HAI, and Dist Vent

This circuit shares a vacuum source on the top of the carburetor and has multiple T's in it to feed multiple items.

79emissionschematic - Ported CB HAI & Dist Vent

Here is a photo of the vacuum source, it is on the top hat of the carb on the front (grill) side of the carb. In this photo it is the nipple pointing toward the camera in between the two that have red caps on them.

IMG_0798[1]

Here is the same thing in the vehicle, labeled 4:

IMG_0772[1]

You can see it goes into a T, one side of the T feeds through a green VTV to the choke breaker, shown here labeled 4 on the right side of the photo:

IMG_0771[1]

Here is a better photo of the choke breaker, it is the gold thing on the top right of the carb, an easy way to tell it from the choke opener (which gets eliminated or connected to atmosphere) is that the nipple coming off of it makes a 90 degree bend.

IMG_0799[1]

That is the choke breaker side of the circuit. The other side of the circuit (left side of the T) feeds the HAI and distributor cap vent. It goes along the top of the air cleaner to another T on the distributor side of the engine.

IMG_0770[1]

I don't have a photo of this T since this is one of the items that I fixed putting things back together.

One side of this feeds the HAI which is the flapper that opens and closes inside the air cleaner to intake air from the hose over the exhaust manifold when the engine is cold, and then switch to intake from the main intake tube once the engine has warmed up.

Here is where the vaccum source connects, to the HAI thermo valve which is on the underside of the air cleaner on the distributor side of the engine, labeled 4:

IMG_0773[1]

And another photo of the same thing from underneath:

IMG_0774[1]

The other hose connects from underneath the air cleaner to the HAI valve which is the gold fitting on top of the air cleaner intake tube (gold thing in the top left quadrant of this photo):

IMG_0770[1]

The last item that this circuit feeds is the distributor cap venting. This vents the distributor cap when the engine is running, and closes that venting when the engine is turned off. This prevents fuel vapors from making their way into the cap when the engine is turned off which could cause an explosion inside the cap when the engine is turned back on.

This is controlled by a VSV which is located under the air cleaner. Shown here:

IMG_0775[1]

NOTE that the hose routing shown in the schematic is incorrect, and is correct in the isometric. The following shows the correct hose routing:

VCVdetail-1

The other thing to note here is the line that goes from the dist cap to a fitting on the firewall, this is the red hose in the following photos:

IMG_0780[1]

IMG_0778[1]

This hose allows circulation of clean interior air through the dist cap when the engine is running.

 

[Toyoland66]

HIC

The HIC isn't really shown on any of the diagrams, it is a gold box that is located on top of the carb on the fender side. The hose connections are from the air cleaner (atmosphere) to the carb insulator. The function as I understand it is to raise idle speed when the engine bay temperatures are high.

79emissionschematic - HIC

Here is a photo of the HIC, it is the gold box in the center of the photo:
IMG_0799[1]

The top connection is shown in this photo, labeled 1:

IMG_0767[1]

The bottom connection connects to the left nipple on the carb insulator (the smaller nipple)
IMG_0817[1]

Here is a photo of it connected in the vehicle:

IMG_0794[1]

 

[Toyoland66]

HAC

HAC is the High Altitude Control, it becomes functional over ~4500 feet elevation and does two things:
-Leans out the fuel mixture to account for thinner intake air
-Adds an additional 6 deg of vacuum advance to the timing

Here is the overall schematic for desmog retaining the HAC:

79emissionschematic - for Desmog - w HAC

Here is the HAC circuit by itself:

79emissionschematic - HAC

The HAC is the only thing that the gas filter is used for in a desmog configuration. The gas filter has two nipples, one of which gets capped, the other of which connects through a check valve, through a T valve, to the high altitude advance port of the distributor. The way I understand it is that the port on the HAC closes at altitude, which then allows this circuit to apply vacuum to the distributor advance. At low altitudes this circuit on the HAC is opened which allows the vaccum to pass through.

If you do not have a functional gas filter (mine was broken and siliconed together) there is a alternative that I have found:

Legris 3121 04 10 Nylon & Nickel-Plated Brass Push-to-Connect Fitting, Inline Standpipe, 4 mm Tube OD x 1/8" BSPT Male
http://www.amazon.com/dp/B009PT8FN6/?tag=ihco-20

IMG_0825[1]

IMG_0827[1]

IMG_0828[1]

Just be aware that the gas filter contains a filter to prevent junk from getting sucked into the intake, so use this alternate at your own risk.

The other function of the HAC is to lean out the carb

Here is a diagram for how it connects on the FJ60:

One thing that differs between the FJ60 and the '79 is that there is no HAC provisions for the slow circuit of the carb, only for the fast circuits. Internally there are inlets into the top of the emulsion tubes which connect through the top of the carb to the ports that are shown with red caps on them in the following photos



as a FYI - the o-rings in my carb were in good shape, the Keister rebuild kit I used did not come with replacement O-rings since it is not made for US market carbs (apparently) but if you do need new O-rings they are toyota part number 21659-38110 and are about $22/ea.

 

[Toyoland66]

Some links to previous threads, for additional reference and info:
https://forum.ih8mud.com/threads/critique-my-79-desmog.728436/
https://forum.ih8mud.com/threads/79-desmog-vacuum-source-for-thermo-valve-hai.471888/

The following document has a lot of good information, it is FJ60 specific and there are some things that are handled differently for the 79-80 FJ40 but this is still a good reference:

forum.ih8mud.com/attachments/how-to-desmog-an-fj60-2-pdf.517068/

There are several fittings in the thermostat housing and intake manifold that can be removed since they no longer serve a purpose. All of these items have BSPT threads, and I was able to find flush fit allen head plugs through McMaster Carr. Additionally McMaster Carr is a good source for silicon caps to cap any nipples that need to be capped. In my experience the black rubber caps that you can buy at the auto parts store do not hold up very well.

A lot of desmog items can also be purchased from JimC (@FJ40Jim) and I believe he has a thread in the classifieds outlining these items.

I hope that this info is useful. It took a lot of reading and sorting through what seems like conflicting information to arrive at this final configuration. I know that this info is pretty specific but the overall functions are applicable to all emission controlled 2F's. The more that you read about this stuff the more you understand how these systems function and why they are plumbed the way they are.

 

[FishTacos]

Why delete the choke opener?

 

[Toyoland66]

Why delete the choke opener?

Not 100% sure of the reason, I will have to research that, I just know that the Guru (JimC) says to eliminate it:

1980 2F de-smog specific questions

Remove the spaghetti pipe assembly, then just install the needed vac hoses.
The choke breaker (upper pot) connects to the center top fitting on front of carb. Other 2 frt fittings are capped.
The choke opener (lower pot) is not needed. Leave it open to atmosphere, or remove it, or connect it to the air cleaner.
Rectangle box is the HIC. Connect to air cleaner on top, and a port located on carb insulator base at the bottom. Note that it is larger than standard vac hose.
Check the other desmog drawing to see which fittings at carb base go where.

 

[Pin_Head]

The definitive desmog is much easier: don't bother. There is nothing to be gained, there is value to be lost and it is a lot of work as detailed above.

 

[KY Longhunter]

Cool. Bookmarked!


...via IH8MUD app

 

[N919HJ]

Thanks for your time and hard work. When all my smog stuff quits and I can't find replacements this will come in handy.

 

[fantic]

Just bought a 79. The PO desmoged it. The red hose on the dist cap is still there. But the other port was left open. What do I need to do with it? Plug it? Run a hose to a vac source?

 

[Toyoland66]

Post #7 shows the hose routing, it goes to a VCV that mounts underneath the air cleaner.

"This vents the distributor cap when the engine is running, and closes that venting when the engine is turned off. This prevents fuel vapors from making their way into the cap when the engine is turned off which could cause an explosion inside the cap when the engine is turned back on."

The VCV is a critical component to this circuit to prevent fuel vapors from entering the cap when the vehicle is not running.

 

[fantic]

I understand this. But all of that stuff has been removed and there is just a K&N air filter on a Webber carb. I'll Probably just plug it.

 

[N919HJ]

If you plug it your dizzy will corrode and stop working correctly. But it is a good excuse to buy a big cap. Hopefully you would vent your big cap though. 78's and earlier didn't have vcv's. The vent went straight from the cap to the air cleaner.

 

[N919HJ]

This what they look like when you don't vent them correctly.