TECH 1 DIAGNOSTICS SERVICE INFO 4.3L TURBO (SYCLONE)

SUBJECT: TECH 1 DIAGNOSTICS FOR TURBOCHARGED 4.3L ENGINE

MODELS: 1991 GMC T PICKUP (SYCLONE)

The 1987-91 TECH 1 Cartridge (P/N TKO2050C) contains the diagnostic information required for the 1991 GMC Syclone equipped with the 4.3L turbo- charged engine. Diagnostics can be accessed either by selecting the VIN engine code or by selecting the appropriate fuel control system.

To access diagnostics, enter the appropriate model year when the following screen is displayed:

GM 87-91 ECM SELECT MODEL YEAR: 19??

To enter diagnostics via VIN engine code, press the "FO" key for VIN when the following screen is displayed:

1991 SELECT

F0:VIN F2:TBI F1:PFI F3:CAD

Vehicles equipped with the 4.3L turbocharged Port Fuel Injection (PFI) engine will have the same engine code (Z) in the eighth position of the VIN as other 4.3LThrottle Body Injection (TBI) engines. As a result of the differences between the two fuel control systems, a specific ECM is required for the turbocharged engine. In order to properly establish communications between the TECH 1 and this "specific" ECM, a special VIN character "S" needs to be entered.

When the following screen is displayed, advance the "Flashing" VIN character by pressing the "NO" key or the "ARROW" keys until the VIN letter "S" flashes. Then press the "YES" key.

SELECT 8TH DIGIT OF VIN CODE: 156789ABCDEFGHJK LNPRSTUXZ

To enter diagnostics via the fuel control system, press the "Fl" key for Port Fuel Injection (PFI) when the following screen is displayed:

1991 SELECT FO:VIN F2:TBI FI:PFI F3:CAD

Advance the TECH 1 fuel control system screens by pressing the "NO" key until the following screen is displayed. Then press the "YES" key.

SELECT PFI ENG. 4.3L TURBO VIN=S SYCLONE TRUCK? 91 (YES/NO)

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.