Mazda MX-5 Miata / Grand Touring. Manual - part 96



If the ratio is 1.5 or more or there is no downstream HO2S inversion, the WU-TWC is functioning 
properly.  



If the ratio is less than 1.5 , the WU-TWC is not functioning properly. Replace the WU-TWC.  

Upstream HO2S Graph Line Example  

Fig. 32: Upstream HO2S Graph Line Example 
Courtesy of MAZDA MOTORS CORP. 

Downstream HO2S Graph Line Example 1  

Equation  

RATIO = 30 inversions (upstream HO2S inversions) divided by 5 inversions (downstream HO2S 
inversions) = 6.0 (good WU-TWC)  

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  

Fig. 33: Downstream HO2S Graph Line Example 1 
Courtesy of MAZDA MOTORS CORP. 

Downstream HO2S Graph Line Example 2  

Fig. 34: Downstream HO2S Graph Line Example 2

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  

Courtesy of MAZDA MOTORS CORP.

Downstream HO2S Graph Line Example 3  

Equation  

RATIO = 30 inversions (upstream HO2S inversions) divided by 27 inversions (downstream HO2S 
inversions) = 1.1 (bad WU-TWC)  

Fig. 35: Downstream HO2S Graph Line Example 3 
Courtesy of MAZDA MOTORS CORP. 

ROLLOVER VALVE REMOVAL/INSTALLATION [LF] 

ROLLOVER VALVE INSPECTION [LF] 

1. Perform the fuel tank inspection. (See FUEL TANK INSPECTION [LF] .)  

FUEL SHUT-OFF VALVE REMOVAL/INSTALLATION [LF] 

NOTE:



The rollover valve cannot be removed as it is built into the fuel tank. 

NOTE:



The rollover valve cannot be removed and inspected as it is built into the 
fuel tank.  

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  

FUEL SHUT-OFF VALVE INSPECTION [LF] 

1. Perform the fuel tank inspection. (See FUEL TANK INSPECTION [LF] .)  

EVAPORATIVE CHAMBER REMOVAL/INSTALLATION [LF] 

1. Remove the battery cover.  

2. Disconnect the negative battery cable. (See BATTERY REMOVAL/INSTALLATION [LF] .)  

3. Disconnect the evaporative hose.  

4. Remove the evaporative chamber.  

5. Cover the evaporative hose with vinyl sheets or the like to prevent them from being scratched or 

contaminated with foreign material.  

6. Install in the reverse order of removal. 

Fig. 36: Identifying Evaporative Chamber & Evaporative Hose 
Courtesy of MAZDA MOTORS CORP.

NOTE:



The fuel shut-off valve cannot be removed as it is built into the fuel tank. 

NOTE:



The fuel shut-off valve cannot be removed and inspected as it is built into 
the fuel tank.  

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata