1985 Porsche 928 AutomaticFACTORY OEM SERVICE PROCEDURE

Ignition Control Signal Test

Disconnect trigger boxes. Connect oscilloscope positive test lead to terminal No. 5 and negative lead to terminal No. 2 of trigger box connector. See Fig 1. Crank engine. Oscilloscope must display a control signal at both trigger boxes.

Fig 1: Ignition Control Signal Test
G34185
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.