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 Bypass valve at WOT (wide open throttle) minimizing engine drag. This dumps the pump's output to the atmosphere, and reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The Bypass 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.
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 Bypass valve at WOT (wide open throttle) minimizing engine drag. This dumps the pump's output to the atmosphere, and reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The Bypass 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.
Yep..... you will only have the solenoid circuit failure codes showing in a KOEO but they will not affect A/F and spark advance strategies, or driveability and performance.
If you find where to hook themup. here is the fix...
TAB & TAD solenoid valve eliminators – eliminate codes 81 & 82.
Edit:TAB & TAD solenoid valve eliminators – eliminate codes 81 & 82.
You will still get 44 & 94 codes because the computer looks for a change in the amount of oxygen in the exhaust by checking the O2 sensors when the solenoids are actuated. Actuating the solenoids provides more oxygen in the exhaust, changing the O2 sensor output. No change and you get the 44 & 94 codes.
Don’t do this if you have a catalytic converter H pipe. The catalytic converters must have the air from the smog pump or they will clog up and choke.
See US - Electronic Components Distributor | Newark.com for the resistors to replace the TAB & TAD solenoids
OHMITE | 43F82RE | Resistors | Passives | Newark.com
If the link fails do a search using the part number
82 ohm, 3 watt wirewound resistor, 94 cents each.
Newark P/N 64K8974
Ohmite part # 43F82RE.
Or use the following part number if the first part number isn't available:
OHMITE | 23J82RE | Resistors | Passives | Newark.com
Newark P/N 64K8241
Ohmite part #23J82RE
Pay a visit to your local Radio Shack to get some heat shrink and some crimp on tap terminals. They do not stock the resistors. Or you can use the Ford connector pin kit from AutoZone.
18 gauge crimp on taps Catalog #: 64-3053
Put the resistor inside the heat shrink tubing and crimp the connectors on. I would choose the Ford pin connectors since they should plug in the TAB & TAD wiring. That way you haven't modified the wiring so it is easy to re-install the TAB & TAD solenoids if emissions testing comes to your area.
Two flat pin connectors.
One 82 ohm, 3 watt resistor.
One piece 3/8" heat sink tubing 2" long.
Two pieces 3/16" heat shrink tubing 1 1/2" long.
Solder the pins onto the resistor leads using electrical solder.
Slide the 3/8" heat shrink tubing over the resistor.
Slide the two pieces of 3/16" heat shrink tubing over the two wires, leaving the flat part of the pins uncovered.
It helps to have the resistor leads straight and not bent as shown in the first picture when you apply heat to the heat shrink tubing. That way, the tubing shrinks more evenly.
Finally, apply heat to shrink all the tubing uniformly.
Bend the leads to fit the spacing on the female TAB & TAD connector sockets.
Push the connector pins of the completed resistor assembly into the empty female TAD or TAD connector sockets on the wiring harness. The resistor assemblies replace the missing solenoids: one resistor assembly per solenoid socket.
Do not crimp on the pins and wrap the mess with electrical tape and say you got the idea from me. If you do, and I hear of it, I will say unkind things about your intelligence and family heritage. Do Quality Work!
This information is for informational purposes only and is intended for use only on off road vehicles. It should not be used on any vehicle operated on public roads.
Operating a vehicle modified in such a manner on public roads is a violation of the EPA codes regarding modification of emission controlled vehicles.
TAB & TAD solenoid valve eliminators – eliminate codes 81 & 82.
Edit:TAB & TAD solenoid valve eliminators – eliminate codes 81 & 82.
You will still get 44 & 94 codes because the computer looks for a change in the amount of oxygen in the exhaust by checking the O2 sensors when the solenoids are actuated. Actuating the solenoids provides more oxygen in the exhaust, changing the O2 sensor output. No change and you get the 44 & 94 codes.
Don’t do this if you have a catalytic converter H pipe. The catalytic converters must have the air from the smog pump or they will clog up and choke.
See US - Electronic Components Distributor | Newark.com for the resistors to replace the TAB & TAD solenoids
OHMITE | 43F82RE | Resistors | Passives | Newark.com
If the link fails do a search using the part number
82 ohm, 3 watt wirewound resistor, 94 cents each.
Newark P/N 64K8974
Ohmite part # 43F82RE.
Or use the following part number if the first part number isn't available:
OHMITE | 23J82RE | Resistors | Passives | Newark.com
Newark P/N 64K8241
Ohmite part #23J82RE
Pay a visit to your local Radio Shack to get some heat shrink and some crimp on tap terminals. They do not stock the resistors. Or you can use the Ford connector pin kit from AutoZone.
18 gauge crimp on taps Catalog #: 64-3053
Put the resistor inside the heat shrink tubing and crimp the connectors on. I would choose the Ford pin connectors since they should plug in the TAB & TAD wiring. That way you haven't modified the wiring so it is easy to re-install the TAB & TAD solenoids if emissions testing comes to your area.
Two flat pin connectors.
One 82 ohm, 3 watt resistor.
One piece 3/8" heat sink tubing 2" long.
Two pieces 3/16" heat shrink tubing 1 1/2" long.
Solder the pins onto the resistor leads using electrical solder.
Slide the 3/8" heat shrink tubing over the resistor.
Slide the two pieces of 3/16" heat shrink tubing over the two wires, leaving the flat part of the pins uncovered.
It helps to have the resistor leads straight and not bent as shown in the first picture when you apply heat to the heat shrink tubing. That way, the tubing shrinks more evenly.
Finally, apply heat to shrink all the tubing uniformly.
Bend the leads to fit the spacing on the female TAB & TAD connector sockets.
Push the connector pins of the completed resistor assembly into the empty female TAD or TAD connector sockets on the wiring harness. The resistor assemblies replace the missing solenoids: one resistor assembly per solenoid socket.
Do not crimp on the pins and wrap the mess with electrical tape and say you got the idea from me. If you do, and I hear of it, I will say unkind things about your intelligence and family heritage. Do Quality Work!
This information is for informational purposes only and is intended for use only on off road vehicles. It should not be used on any vehicle operated on public roads.
Operating a vehicle modified in such a manner on public roads is a violation of the EPA codes regarding modification of emission controlled vehicles.