1989 GMC Forward Control 7.4 W, StandardFACTORY OEM SERVICE PROCEDURE

Electronic Control Module (ECM)

The Electronic Control Module (ECM) receives and processes information from all data sensors to produce the proper pulse duration ("on" time) for the injector(s), correct idle speed and proper spark timing. The ECM performs calculations to control the following operating conditions: engine start, engine running, fuel enrichment during acceleration, lean fuel mixture during deceleration, fuel cut-off and battery voltage correction.

If the engine is flooded, the driver must depress the accelerator pedal all the way down. At this position, the ECM calculates injector pulse width equal to an air/fuel ratio of 20:1. This air/fuel ratio will be maintained as long as the throttle valve remains wide open and engine speed is below 600 RPM. If the throttle position becomes less than 80 percent open and/or engine speed exceeds 600 RPM, the ECM changes the injector pulse width to that used during engine starting.

Factory Service Tools

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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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