Mode I and II (Mixture Ratio Feedback Control)

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. 55 Inspecting E.C.U. Lamps:

3. Make sure that the green L.E.D. on the E.C.U. (located on the floor board in front of the center console) flashes on and off more than 5 times in 10 seconds at 2000 rpm under no load.
a. If OK proceed to step 4. The O2 sensor is operating properly.
b. If not OK, proceed to step 7.
4. Race the engine 2 or 3 times, then idle.

Fig. 52 Selecting Modes:

5. Turn the diagnostic mode selector on the E.C.U. fully clockwise and wait for the L.E.D.`s to flash 2 times, then immediately turn the selector counterclockwise. The ECCS system is now in "Mode 2".
6. Make sure that both L.E.D.'s flash more than 5 times in 10 seconds at 2000 rpm under no load.
a. If OK, mixture feedback operation (air/fuel mixture) is correct. Proceed to step 7 and END TEST.
b. If not OK, proceed to step 8.
7. Turning the engine off will return the ECCS system to "Mode 1" (normal operating mode).
8. Turn the engine off and disconnect the negative battery terminal.
9. Disconnect the harness from the ECU.

Fig. 148 O2 Sensor Harness Inspection:

10. Disconnect the O2 sensor connector and use a jumper wire to ground the center terminal in the harness connector to the body or engine (not the sensor wire).
11. With an ohm meter, check for continuity between connector 29 in the ECU harness and body ground.
a. If OK, proceed to step 12.
b. If not OK, check harness for an open circuit.
12. Reconnect ECU and O2 sensor harness jumper wire (do not reconnect the O2 sensor).

Fig. 64 Engine Temperature Sensor:

12. Disconnect engine temperature sensor connector.
13. Install a 2.5k ohm resistor to the harness connector.
14. Reconnect battery ground cable.
15. Start the engine and warm to operating temperature.
16. Check the exhaust CO content with an exhaust gas analyzer.
a. If CO is between 0.2 and 8.0% at idle, replace the O2 sensor and proceed to step 1.
b. If the CO is not with the given tolerances, proceed to step 17.
17. Turn the engine off and reconnect the O2 sensor and engine temperature sensor.
a. Refer to ELECTRICAL COMPONENT AND CIRCUIT DIAGNOSIS and check the following components:
^Air flow meter.
^Fuel injector.
^Engine temperature sensor.
^Fuel pressure regulator control circuit.
c. Refer to FUEL SYSTEMS and check the fuel pressure regulator.