DFI System Check

The DFI SYSTEM CHECK is an organized approach for identifying a problem caused by DFI system. Driver comments normally fall into one of the following: steady "SERVICE NOW/SOON" lights, driveability problems, engine will not start, or engine stalls after start.

1. Lighting of "SERVICE NOW/SOON" lights during cranking confirms power and ground to ECM.
2. If "SERVICE NOW/SOON" light is on with engine running, check for ECM codes. Diagnose codes before proceeding with system check. Refer to the DFI ECM TESTS/CODES article in this section.
3. After codes are corrected, ability of DFI system to control fuel delivery to engine must be checked.
4. Checks for proper closed/open loop operation.
5. If closed loop is achieved, fuel system has to be checked for rich, lean or proper fuel control. The DFI system has ECM data parameter P.1.4 integrator. This monitors oxygen sensor rich/lean status and drives fuel system richer if oxygen sensor is lean, or leaner if sensor is rich. The integrator has a range of 60-160 counts. The integrator value will be 128 when ECM does not have to modify fuel rate to engine. The integrator will reset to 128 if fuel system is in acceleration, power enrichment, some deceleration or open loop modes. The integrator resets to 128 when oxygen sensor is not in control of fuel. If integrator sees an oxygen sensor that is lean most of the time, the integrator value will go higher to try and add more fuel to engine. If integrator sees an oxygen sensor that is rich most of the time, the integrator value will go lower to try and drive fuel system leaner.
6. In this test, operate engine in closed loop (1000-2000 RPM with steady throttle) to stabilize integrator reading of 88-160. In most cases, this will indicates that fuel delivery system is okay.

Fig 1: DFI System Check Flow Chart

Fig 2: DFI System Check Flow Chart (1 Of 2)

Fig 3: DFI System Check Flow Chart (2 Of 2)