Purpose of inspection
To determine whether the malfunction is a rich or a lean air fuel mixture.
Criteria
Using an intelligent tester, check the voltage of the O2 sensor or short term fuel
trim.
The factors that change the A/F balance
(1) When the A/F ratio is small (rich)
Consider the factors that cause the fuel system injection amount to increase, or inject continuously
• Sensor range/performance problem
• Poor contact with the ground of the sensor system
• Injector dribbling
etc.
(2) When the A/F ratio is great (lean)
Consider the factors that cause the fuel system injection amount to decrease.
• Sensor range/performance problem
• Fuel pressure is low
• Poor contact with the ground of the injector system
• O2 sensor system malfunction (the signal shows the mixture is rich)
• Absorption of fuel due to carbon accumulation
etc.