You need Java to see this applet.
                          Emissions: Air Bypass Valve and Air Diverter Valves

There are a majority of us who haven't completely gutted our Mustangs engine bay and still run with the
emissions system in-tact.  The smog pump, air bypass valve, air diverter valve, and assorted solenoids play
a major roll in the proper function of the system.  This page should give you a basic idea of the components
function and how the system is designed.

The heat shield wrap on the lower hose is not a standard feature.  I found that this hose is rather close to
aftermarket headers and I kept burning through that hose.  The above set-up is for my supercharged vehicle,
so the hose lengths may be slightly different than what you see on your car.

Air Bypass Valve

Air flows down the hose from the smog pump to the Air Bypass Valve.  

  •  With no vacuum at the valve, air is diverter out the bottom of the valve to the atmosphere.  
                The air is directed to the atmosphere under deceleration.
  •  With vacuum at the valve, air continues down the hose to the Air Diverter Valve.  

Air Diverter Valve

As the air enters the Air Diverter Valve it has two choices, it either flows to the back of the heads or
to the catalytic converters.  

  •  With no vacuum at the valve, air flows downward in the valve toward the catalytic converters.
  •  With vacuum at the valve, air continues to the back of the heads.

Check Valve

At the entrance to the pipes leading to the heads and catalytic converters there are one
way check valves.  The one mounted on the pipe leading to the heads is replaceable
(Ford: E9VE-9A487-AB).  The one mounted on the pipe to the converters is crimped on and
not easily replaced.  You will probably need a new assembly.

TAB (Thermactor Air Bypass) Solenoid
TAD (Thermactor Air Diverter) Solenoid

                                    The Air Bypass and Air Diverter valves are computer controlled
                                    solenoids mounted between the passenger side firewall
                                    and strut tower.  These solenoids are referred to as the
                                    TAB and TAD solenoids.  In the picture to the left they are
                                    the two black solenoids mounted side by side.  They receive
                                    vacuum from the upper intake and distribute vacuum by way
                                    of the small square vacuum junction located between the
                                    strut tower and valve cover / throttle body.  


Vacuum Lines

The four vacuum lines that feed off the vacuum junction box into the engine bay are as follows:

  •  Vacuum source from the upper intake
  •  Vacuum feed to the EGR at the rear of the throttle body
  •  Vacuum feed to the Air Bypass Valve
  •  Vacuum feed to the Air Diverter Valve
  •  There is a 5th vacuum port but it is not used.