GSIC - Global Service Information Center

### SFI SYSTEM > Variable Resistor Circuit

## for Preparation Click here

## 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, making the air-fuel mixture a little richer.

## WIRING DIAGRAM

## INSPECTION PROCEDURE

1.CHECK CO/HC

1. Warm up the engine to normal operating temperature.

1. Turn all accessories OFF.

1. Connect all vacuum lines properly.

1. Connect the tachometer.

1. Check ignition timing correctly.

1. Check idle speed correctly.

1. Check that the CO meter is properly calibrated.

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

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

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

   Idle CO concentration:
     1 to 2%

| OK |

CHECK FOR PROBLEM SYMPTOMS TABLE

NG |

2.ADJUST CO CONCENTRATION

1. Put the vehicle in the same condition as the previous step (CHECK CO/HC).

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

   Result
   Result | Proceed
   Concentration: 1.5 +- 0.5% | B
   Change in CO concentration | C
   No change in CO concentration | A

   HINT:
   1. Always check idle speed after turning the idle mixture adjusting screw. If it is incorrect, readjust idle speed.
   2. The idle mixture adjusting screw can be turned within 180°. Do not turn this screw more than specified.

SST
  09243-00020

| B |

ADJUSTMENT COMPLETE

| C |

CHECK CO/HC

A |

3.INSPECT VARIABLE RESISTOR

1. 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

1. While fully turning the idle mixture adjusting screw clockwise and counterclockwise using SST, measure the resistance.

   Resistance:

     Tester Connection | Specified Condition
     2 - 3 | Voltage changes from approximately 5 to 0 kΩ

SST
  09243-00020

| NG |

REPLACE VARIABLE RESISTOR

OK |

4.CHECK ECM (VAF VOLTAGE)

1. Turn the ignition switch ON.

1. While fully turning the idle mixture adjusting screw clockwise and counterclockwise slowly using SST, measure the voltage.

   Voltage:

     Tester Connection | Specified Condition
     VAF (E12-25) - E2 (E12-28) | Voltage changes smoothly from 0 to approximately 5 V (does not change suddenly)

SST
  09243-00020

| OK |

REPLACE ECM

NG |

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

1. Disconnect the V4 variable resistor connector.

1. Disconnect the E12 ECM connector.

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

   Standard (check for open):

     Tester Connection | Specified Condition
     VC (V4-2) - VC (E12-18) | Below 1 Ω
     VAF (V4-3) - VAF (E12-25) | Below 1 Ω
     E2 (V4-1) - E2 (E12-28) | Below 1 Ω

   Standard (check for short):

     Tester Connection | Specified Condition
     VC (V4-2) or VC (E12-18) - Body ground | 10 kΩ or higher
     VAF (V4-3) or VAF (E12-25) - Body ground | 10 kΩ or higher

| NG |

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK |

REPLACE ECM