SFI SYSTEM (w/o Secondary Air Injection System) Variable Resistor Circuit

DESCRIPTION

This resistor is used to change the air-fuel ratio of the air-fuel mixture.

The idle mixture is adjusted using this resistor.

Turning the idle mixture adjusting screw clockwise moves the contacts inside the resistor, raising the terminal VAF voltage. Conversely, turning the screw counterclockwise lowers the terminal VAF voltage.

When the terminal VAF voltage rises, the ECM increases the injection volume slightly, marking the air-fuel mixture a little richer.

WIRING DIAGRAM

A01BBAYE01

INSPECTION PROCEDURE

Note

Always use a CO meter when adjusting the idle mixture. If a CO meter is not available, DO NOT ATTEMPT TO ADJUST IDLE MIXTURE.

PROCEDURE


  1. CHECK CO/HC


    1. Warm up the engine to normal operating temperature.

    2. Switch all accessories OFF.

    3. Connect all vacuum lines properly.

    4. Connect the tachometer.

    5. Check ignition timing correctly.

    6. Check idle speed correctly.

    7. Check that the CO meter is properly calibrated.

    8. Race the engine at 2,500 rpm about 2 minutes.

    9. Insert a tester probe at least 40 cm (1.3 ft) into the tailpipe.

    10. Measure the concentration for 1 to 3 minutes after racing the engine to allow the concentration to stabilize.

      Idle CO concentration
      1.0 to 2.0 %

    OK

    CHECK FOR PROBLEM SYMPTOMS TABLE

    NG

  2. ADJUST CO CONCENTRATION


    1. A01BHU5E01

      Put the vehicle in the same condition as step 1 of this chart.

    2. Using SST, adjust the idle mixture by turning the idle mixture adjusting screw in the variable resistor.

      Result
      Result Proceed to
      Concentration: 1.0 to 2.0 % B
      Change in CO concentration C
      No change in CO concentration A

      Tech Tips


      • Always check idle speed after turning the idle mixture adjusting screw. If it is incorrect, readjust idle speed.

      • The idle mixture adjusting screw can be turned within 180 degrees. Do not turn this screw more than the specified.

      SST
      09243-00020

    B

    ADJUST COMPLETE

    C

    CHECK CO/HC

    A

  3. INSPECT VARIABLE RESISTOR


    1. A01BF7RE01

      Measure the resistance according to the value(s) in the table below.

      Resistance
      Tester Connection Specified Condition
      1 - 2 3.5 to 6.5 Ω

    2. Measure the resistance according to the value(s) in the table below, when turning the idle mixture adjusting screw fully clockwise and counterclockwise using SST.

      Resistance
      Tester Connection Specified Condition
      2 - 3 Change from about 5 kΩ to 0 kΩ accordingly
      SST
      09243-00020

    NG

    REPLACE VARIABLE RESISTOR

    OK

  4. CHECK ECM (VAF VOLTAGE)


    1. A01BF4UE02

      Turn the ignition switch to the ON position.

    2. Measure the voltage according to the value(s) in the table below while slowly turning the idle mixture adjusting screw first fully counterclockwise and then fully clockwise, using SST.

      Voltage
      Tester Connection Specified Condition
      VAF (D1-25) - E2 (D1-28) Voltage changes smoothly from 0 V to about 5 V, i.e. does not suddenly jump up to 5 V down to 0 V
      SST
      09243-00020

    OK

    REPLACE ECM

    NG

  5. CHECK HARNESS AND CONNECTOR (VARIABLE RESISTOR - ECM)


    1. A01BC5RE02

      Disconnect the D31 variable resistor connector.

    2. Disconnect the D1 ECM connector.

    3. Measure the resistance according to the value(s) in the table below.

      Resistance (check for open)
      Tester Connection Specified Condition
      VC (D31-2) - VC (D1-18) Below 1 Ω
      VAF (D31-3) - VAF (D1-25) Below 1 Ω
      E2 (D31-1) - E2 (D1-28) Below 1 Ω
      Resistance (check for short):
      Tester Connection Specified Condition
      VC (D31-2) or VC (D1-18) - Body ground 10 kΩ or higher
      VAF (D31-3) or VAF (D1-25) - Body ground 10 kΩ or higher

    4. Reconnect the ECM connector.

    5. Reconnect the variable resistor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

    REPLACE ECM