Air/Fuel Mixture: Testing and Inspection
IDLE MIXTURE CHECKRequired Special Tool: MB991502: Scan Tool (MUT-II)
1. Before inspection, set the vehicle to the following condition.
- Engine coolant temperature: 80 - 95°C (176 - 203°F)
- Lights and all accessories: OFF
- Transmission: P range
2. Connect scan tool MB991502 to the data link connector.
3. Check to be sure that the basic ignition timing is at the standard value.
Standard value: 5° BTDC ± 3°
4. Start the engine and increase the engine speed to 2,500 r/min for two minutes.
5. Connect a CO and HC tester.
6. Check the CO contents and the HC contents while the engine is idling.
Standard value:
CO contents: 0.5% or less
HC contents: 100 PPM or less
7. If the concentrations are outside the standard values, check the following items.
NOTE: If the results of the checks for all items are normal but the CO and HC concentrations still exceed the standard values, replace the three-way catalyst.
- Diagnostic output
- Closed loop control
(If closed loop control is being carried out normally, the heated oxygen sensor output signal will vary between 0 - 400 mV and 600 - 1,000 mV while the engine is idling.)
- Fuel pressure
- Injectors
- Ignition coil, spark plug cables, spark plugs
- Evaporative emission control system
- Compression pressure