Smog delete in back of heads but keeping smog pump?

jd-hart · Jul 25, 2008

I am sure this has been answered but I cannot find it searching.

I am installing some new heads and wanted to plug the emissions port in the back of the heads. I need to keep the smog pump due to my bassani catted x-pipe.

Can I just plug the end of the valve that is after the air check valve? Not sure what this is called but it has a port on each side and one on the bottom. The bottom one goes to the cats. For the other ports, one comes from the air check valve and one goes to the back of the heads. I would just like to cap the one going to the heads. Is this possible?

NIKwoaC · Jul 26, 2008

I don't think that makes a lot of sense to do. You should either keep the whole system or get rid of it. The smog pump feeds the heads when the engine is cold, then feeds the mid-pipe as it warms up. If you want to keep part of it, and the new heads have the provisions for it, just keep running the whole system.

Beasty306GT · Jul 26, 2008

cant do that....u need to remove the whole smog system

jrichker · Jul 26, 2008

Thermactor Air System
Some review of how it works...

The Thermactor air pump (smog pump) supplies air to the heads or catalytic converters. This air helps break down the excess HC (hydrocarbons) and CO (carbon monoxide). The air supplied to the catalytic converters helps create the catalytic reaction that changes the HC & CO into CO2 and water vapor. Catalytic converters on 5.0 Mustangs are designed to use the extra air provided by the smog pump. Without the extra air, the catalytic converters will clog and fail.

The Thermactor air pump draws air from an inlet filter in the front of the pump. The smog pump puts air into the heads when the engine is cold and then into the catalytic converters when it is warm. The Thermactor control valves serve to direct the flow. The first valve, TAB (Thermactor Air Bypass) or AM1 valve) either dumps air to the atmosphere or passes it on to the second valve. The second valve, TAD (Thermactor Air Diverter valve or AM2 valve) directs it to the heads or the catalytic converters. Check valves located after the TAB & TAD solenoids prevent hot exhaust gases from damaging the control valves or pump in case of a backfire. The air serves to help consume any unburned hydrocarbons by supplying extra oxygen to the catalytic process. The computer tells the Thermactor Air System to open the dump valve at WOT (wide open throttle) minimizing engine drag. The dump valve reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The dump valve also opens during deceleration to reduce or prevent backfires.

Computer operation & control for the Thermactor Air System
Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the computer side of the wire will drop down to 1 volt or less.

In order to test the TAD/TAB solenoids, you need to ground the white/red wire on the TAB solenoid or the light green/black wire on the TAD solenoid.

For 94-95 cars: the colors are different. The White/Red wire (TAB control) is White/Orange (Pin 31 on the PCM). The Green/Black wire (TAD control) should be Brown (pin 34 at the PCM). Thanks to HISSIN50 for this tip.

To test the computer, you can use a test light across the TAB or TAD wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker.

It is possible to run the hose from the Dump valve directly to the check vavle that feeeds the cats. However, I would leave the whole system intact and working

SickSix said:
cant do that....u need to remove the whole smog system

Bad plan -the 2-4 HP and 10 lbs you save isn't worth it. I will be polite and refrain from making any unkind remarks about your intelligence or education.

Beasty306GT · Jul 26, 2008

jrichker said:
Thermactor Air System
Some review of how it works...

The Thermactor air pump (smog pump) supplies air to the heads or catalytic converters. This air helps break down the excess HC (hydrocarbons) and CO (carbon monoxide). The air supplied to the catalytic converters helps create the catalytic reaction that changes the HC & CO into CO2 and water vapor. Catalytic converters on 5.0 Mustangs are designed to use the extra air provided by the smog pump. Without the extra air, the catalytic converters will clog and fail.

The Thermactor air pump draws air from an inlet filter in the front of the pump. The smog pump puts air into the heads when the engine is cold and then into the catalytic converters when it is warm. The Thermactor control valves serve to direct the flow. The first valve, TAB (Thermactor Air Bypass) or AM1 valve) either dumps air to the atmosphere or passes it on to the second valve. The second valve, TAD (Thermactor Air Diverter valve or AM2 valve) directs it to the heads or the catalytic converters. Check valves located after the TAB & TAD solenoids prevent hot exhaust gases from damaging the control valves or pump in case of a backfire. The air serves to help consume any unburned hydrocarbons by supplying extra oxygen to the catalytic process. The computer tells the Thermactor Air System to open the dump valve at WOT (wide open throttle) minimizing engine drag. The dump valve reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The dump valve also opens during deceleration to reduce or prevent backfires.

Computer operation & control for the Thermactor Air System
Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the computer side of the wire will drop down to 1 volt or less.

In order to test the TAD/TAB solenoids, you need to ground the white/red wire on the TAB solenoid or the light green/black wire on the TAD solenoid.

For 94-95 cars: the colors are different. The White/Red wire (TAB control) is White/Orange (Pin 31 on the PCM). The Green/Black wire (TAD control) should be Brown (pin 34 at the PCM). Thanks to HISSIN50 for this tip.

To test the computer, you can use a test light across the TAB or TAD wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker.

It is possible to run the hose from the Dump valve directly to the check vavle that feeeds the cats. However, I would leave the whole system intact and working

Bad plan -the 2-4 HP and 10 lbs you save isn't worth it. I will be polite and refrain from making any unkind remarks about your intelligence or education.

Oh yeah buddy..i aint no mechanic like you...keep your comments to yourself...My intelligence makes me 60k plus a yr.

justboughthelx · Jul 26, 2008

Most impressive thread I have read on the emissions. Thanks for the info.

jrichker · Jul 26, 2008

SickSix said:
Oh yeah buddy..i aint no mechanic like you...keep your comments to yourself...My intelligence makes me 60k plus a yr.

I am not a mechanic by trade, I am a Microsoft MCSE and do computers and networks for a living. My mechanical and electronics background enables me to help others understand the computer controlled engine & troubleshoot problems with it.

LiquidGT · Jul 26, 2008

I'm running my car with "half" emissions, I have cats for the time being and I dont have Explorer GT40s with no thermactor. I just left the pipe off the back of the heads and left the check valve on the diverter valve.

tiptop · Jul 26, 2008

sure you can, just plug off the holes in the back of the heads, ten remove the rubber hose off of the smog pump that goes to the exhaust pipe, your smog pump will still spin as normal, but the air will just go out the end of the short little pipe.

GreatWhite · Jul 26, 2008

If you have aftermarket cats... then just yank the whole system. Aftermarket high flows do not have provisions for the air pump hookup; only stockers do.

v8only · Jul 26, 2008

the air that goes to the back of the heads when cold simply goes back out the exhaust headers, and simply tricks the o2 sensors into a lean condition, thus richening the mixture for cold startups.

It's completely and utterly unimportant for warm driving emissions, and won't effect cold startups either. I'm a cali nazi land guy, and run strict emissions, but do NOT run the bypass tubing to the heads, and have no issues.

What I would do in your case is to simply run a straight tube from the back of the smog pump directly into the h pipe. I'd delete everything else, including the tab and tad soloniods. Your emissions will be fine.

99% of the smog techs out there aren't familiar with that old school crap anyhow, and if you keep it looking OEM, you'll never get questioned. You will have a check engine light though for tab and tads. since the air diverts to the h pipe/cats when warm anyhow, no harm no foul.

jrichker · Jul 26, 2008

v8only said:
the air that goes to the back of the heads when cold simply goes back out the exhaust headers, and simply tricks the o2 sensors into a lean condition, thus richening the mixture for cold startups.

It's completely and utterly unimportant for warm driving emissions, and won't effect cold startups either. I'm a cali nazi land guy, and run strict emissions, but do NOT run the bypass tubing to the heads, and have no issues.

What I would do in your case is to simply run a straight tube from the back of the smog pump directly into the h pipe. I'd delete everything else, including the tab and tad soloniods. Your emissions will be fine.

99% of the smog techs out there aren't familiar with that old school crap anyhow, and if you keep it looking OEM, you'll never get questioned. You will have a check engine light though for tab and tads. since the air diverts to the h pipe/cats when warm anyhow, no harm no foul.

That is also not the best plan. In doing so, you have elminated the ability to dump the load from the pump by removing the bypass valve. The bypass valve opens at WOT, removing the load from the pump and reducing the parasitic drag to 2-4 HP or less. Go back and read my Thermactor Air System Therory and operation and you will get a better understanding.

v8only · Jul 26, 2008

sometimes you just don't have a choice in things.

fortunately I've been running this setup for some time with no issues, and passed cali smog with flying colors.

lang williams · Jul 26, 2008

I had a set of ported E7's a while a go an I couldn't remove the plugs. I just plugged the tube going to the back of the heads an left the rest of the system as is...It passed the Ohio E check an the numbers were really good. This wasn't a daily driver though an I only drove it about 1500 miles a year so I don't know if there'd be any long term probs from this.

v8only · Jul 26, 2008

on most high mileage 5.0's, when you remove the bypass tubing from the head, you'll find that the holes are 100% carboned up. I've come across this on more than one occasion. This essentially renders the system useless in the same mannor that eliminating it would.

Ryno8705 · Jul 31, 2008

v8only said:
the air that goes to the back of the heads when cold simply goes back out the exhaust headers, and simply tricks the o2 sensors into a lean condition, thus richening the mixture for cold startups.

FYI, the computer ignores the O2 sensors until the engine is warmed up. Until then the computer controls the engine based off preset tables, ie: open loop... The O2 sensors just sit there and warm up until the systems enters closed loop. So, not quite sure why you think the O2 sensors are tricked, they are ignored. Do a search on open loop and closed loop.

Blucifer99 · Aug 29, 2018

So what if i kept the bypass valve that dumps the load at wot and ran the bypass valve to the cats and removed the air tube to the heads wouldnt that still work. Thats my plan for when i swap to my promaxx heads that arnt smogg legal... I figured have the smogg pump go directly into the cats by removing the thermactor air tube and diverter valve and keeping the bypass valve.. To me that seems like it would work plenty fine. Id just have to figure out how to not have a check engine light because of the tad solenoid not bein used..

Mustang5L5 · Aug 29, 2018

I covered this in a thread a few months ago. Let me see if I can find it. Basically I remove the diverter and keep the bypass and only run the single line to the h pipe.

As for the TAD it doesn't matter what you do because the computer checks operation by looking for a change in the o2 sensor readings when air is pumped to the heads. I'd just cap the vac line off the solenoid. A code will be generated but it doesn't throw them light or affect how the car runs.

Most of those head ports are carboned up at this point it doesn't matter. My car has a permanent code due to, what I assume, is one side blocked up.

Blucifer99 · Aug 30, 2018

Mustang5L5 said:
I covered this in a thread a few months ago. Let me see if I can find it. Basically I remove the diverter and keep the bypass and only run the single line to the h pipe.

As for the TAD it doesn't matter what you do because the computer checks operation by looking for a change in the o2 sensor readings when air is pumped to the heads. I'd just cap the vac line off the solenoid. A code will be generated but it doesn't throw them light or affect how the car runs.

Most of those head ports are carboned up at this point it doesn't matter. My car has a permanent code due to, what I assume, is one side blocked up.

Ahh see ive checked all the ports on my heads and stuff and its clean and not plugged. So when i remove the diverter and air tube and then plug the vac line what if i left the tad valve plugged in but "open to air" you think it would throw a code? Like if i plug the vac line there will be no vacuum leak but with the tad still plugged in and working per say u think it would throw a cel?

Mustang5L5 · Aug 30, 2018

It's going to trip the code because the ECU looks for a change in o2 response from the added air to the exhaust upstream of the cats. THats how the ECU knows the system works. The solenoid itself is dumb. JUst cap the vac line to the TAD after the solenoid and leave in place (or unplug and remove completely)

The code doesn't change how the car runs and doesn't trip the light

Smog delete in back of heads but keeping smog pump?

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