1989 GMC Forward Control 3.9 L, StandardFACTORY OEM SERVICE PROCEDURE

Fuel Injection System - TBI: Identification

The throttle body injection identification number is stamped on mounting flange, on throttle lever side. See Figure. Alphabetical code letters are stamped on the throttle body at external tube locations to identify vacuum hose connections. All 4-cylinder engines are equipped with model 700 TBI unit. The V6 and V8 engines use model 220 TBI unit.

Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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