Computers and Control Systems: Application and ID

The Speed Density Update attribute contains the Driveability and Emissions system diagnostics for those 1987 and 1988 vehicles equipped with 2.8L (VIN W) engines using speed density fuel control systems. To determine if a vehicle is equipped with a speed density fuel control system, refer to either the upper right hand shock tower and/or the Engine Control Module (ECM) Mem-Cal access door. If there is no label to indicate that a speed density fuel control system is being used, refer to section "6E", "Driveability and Emissions" of the appropriate divisional service manual for Mass Air Flow (MAF) fuel control system.

A second method to determine if the vehicle is using speed density fuel control is by utilizing the "scanner". "Scan" selections will not read data on a speed density vehicle for 1987-1988. Data can be read if 1989 is selected as the model year. PROM ID will match either 1987-1988 GM SPO CAMS/T-10/T-15 information for Mass Air Flow or Speed Density vehicle fuel control. TECH I and CAMS functions, including test directors and automated routines, should be selected according to fuel control system. A final method to determine if the update has has been performed is to inspect the (MAF) relay. If the update has been performed the MAF relay will be disconnected. This disables the MAF portion of the MAF/Manifold Air Temperature (MAT) assembly while leaving the MAT sensor operational.

The Speed Density update information combines the 1987-1988 Mass Air Flow original wiring configurations and service bulletins, with the appropriate modifications for the Speed Density Application. Note again that if the vehicle is a speed density configuration, use the 1989 2.8L "Scan" selection. Refer to Service bulletins for proper Mem-Cal Selection.