1991 Geo Prizm LSi, StandardFACTORY OEM SERVICE PROCEDURE

Electronic Ignition Timing Advance

Ignition timing is controlled by the Electronic Control Module (ECM). On Prizm GSi, a knock sensor, located in rear of cylinder block, sends a variable AC voltage signal to ECM depending on engine detonation. The ECM uses this signal to determine if ignition timing should be retarded.

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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