IF YOU ARE CHANGING YOUR DOWNPIPE AND/OR CATBACK IT IS RULE OF THUMB TO REPLACE YOUR O2 SENSORS
Upstream(on downpipe) and Downstream(near second cat) sensors are responsible for measuring the exhaust as it comes out of the engine. This information is used by your ECU to adjust fuel trims. Failed oxygen sensors can cause a check engine light as well as major performance issues.
AFR(Air Flow Ratio) – Measured by your Upstream/Main O2, your air-fuel ratio is vital to watch and monitor if you are modifying or trying to make more power. Your Mazdaspeed is tuned to hit certain AFR targets and relies on the O2 sensor and the MAF Sensor (Mass Air Flow) to adjust fuel delivery accordingly.
However, there are things that can interfere with how these sensors communicate with the ECU, and if this happens, it will throw your system out of whack
Oxygen Sensor
Your vehicle's oxygen sensor works with your engine control unit to optimize your engine's performance. The oxygen sensor is measure the proportion of oxygen in the exhaust sends input back to the engine control unit so it can modify the vehicle's air fuel ratio based off of it's current conditions. In doing so your Oxygen Sensor is a major part of your vehicle engine management and fuel consumption.
Oxygen Sensor Failure Symptoms
- Reduced fuel mileage
- Failed emissions testing
- A check engine light
- Poor drive-ability
Mazdaspeed Various Sensors
This is responsible for allowing gas fumes from your EVAP system to be purged into your induction system to be burned off. However, the solenoid can sometimes be stuck open, and allow unmetered air in at the wrong times.
The simplest way to test the EVAP purge solenoid is to remove its inlet and outlet hoses, remove the electric plug and test if air is passing through at all times. If so, replace. If not, applying 12VDC to contacts should allow air to pass through. If not, again, replace. Otherwise, the solenoid is doing what it’s supposed to do.