Air/Fuel Mixture: Adjustments

Air/fuel mixture is not adjustable.
The following procedure will describe inspection of the mixture ratio feedback system.
1. Start the engine and warm it up until the water temperature indicator points to the middle of the gauge.
2. Operate the engine at 2000 rpm for 2 minutes under no load.

Fig. 4 ECU Location:

3. Turn the diagnostic mode selector on the E.C.U (located under a panel in the R.F. footwell) fully clockwise and wait for at least 2 seconds, then immediately turn the selector counterclockwise. The ECCS system is now in the mixture ratio feedback inspection mode.

Fig. 54 Inspecting ECU Lamp:

4. Observe the diode at the ECU (indicating the left O2 sensor signal).
a. If the diode flashes more the 5 times in 10 seconds proceed to step 5.
b. If the diode flashes less than 5 times in 10 seconds, turn the engine off. Replace the left O2 sensor and proceed to step 1 again. If the system fails these procedures again, proceed to step 27.
c. If the diode does not flash proceed to step 7.

Fig. 53 Changing O2 Inspection Mode:

5. Turn the diagnostic mode selector on the E.C.U. fully clockwise and wait for at least 2 seconds, then immediately turn the selector counterclockwise.
You will now be inspecting the right O2 sensor signal.
6. Observe the diode at the ECU (indicating the right O2 sensor signal).
a. If the diode flashes more the 5 times in 10 seconds, the mixture feedback system is operating normally. END OF TEST.
b. If the diode flashes less than 5 times in 10 seconds, replace the right O2 sensor and proceed to step 1 again. If the system fails these procedures again, proceed to step 27.
c. If the diode does not flash proceed to step 17.
7. Turn the engine off and disconnect the negative battery cable.
8. Disconnect the 76 pin connector from the ECU.
9. Disconnect the left O2 sensor connector.

Left O2 Sensor Terminals:

10. Using an ohm meter, check continuity between the middle terminal of the harness at the sensor and terminal 55 of the ECU connector.
a. If continuity does not exist, check the harness for cut, broken or damaged areas (there are no other connector between the ECU and sensor).
b. If continuity does exist, reconnect the ECU connector and proceed to step 11.
11. Disconnect the AIV solenoid connector (located near the battery and cruise control vacuum actuator).
12. Disconnect the engine temperature sensor connector (located in the radiator outlet tube, near the top of the fan shroud) and install a 2.5k ohm resistor across the terminals in the harness.
13. Reconnect the negative battery cable.
14. Start the engine and warm to operating temperature.
15. Race the engine 3 or 4 times (in neutral) and then return to idle.
16. Using an exhaust gas analyzer, check the CO content from either exhaust pipe.
a. If the CO is between 0.2 and 8.0%, turn the engine off, reconnect the engine temperature sensor and AIV solenoid, and proceed to step 1.
b. If the CO is not between 0.2 and 8.0% proceed to step 27.
17. Turn the engine off and disconnect the negative battery cable.
18. Disconnect the 76 pin connector from the ECU.
19. Disconnect the left O2 sensor connector.

Right O2 Sensor Terminals:

20. Using an ohm meter, check continuity between the middle terminal of the harness at the sensor and terminal 29 of the ECU connector.
a. If continuity does not exist, check the harness for cut, broken or damaged areas (there are no other connector between the ECU and sensor).
b. If continuity does exist, reconnect the ECU connector and proceed to step 11.
21. Disconnect the AIV solenoid connector (located near the battery and cruise control vacuum actuator).
22. Disconnect the engine temperature sensor connector (located in the radiator outlet tube, near the top of the fan shroud) and install a 2.5k ohm resistor across the terminals in the harness.
23. Reconnect the negative battery cable.
24. Start the engine and warm to operating temperature.
25. Race the engine 3 or 4 times (in neutral) and then return to idle.
26. Using an exhaust gas analyzer, check the CO content from either exhaust pipe.
a. If the CO is between 0.2 and 8.0%, turn the engine off, reconnect the engine temperature sensor and AIV solenoid, and proceed to step 1.
b. If the CO is not between 0.2 and 8.0% proceed to step 27.
27. Inspect the following components and/or circuits and repair faults and proceed to step 1.
^Fuel pressure.
^Air flow meter.
^Fuel injector.
^Engine temperature sensor.
^Substitute a known good ECU and recheck.
It is not likely that the ECU is faulty, but in certain circumstances, this may be the cause.