1991 Pontiac Firebird Formula, 5.0 F, Standard, M39FACTORY OEM SERVICE PROCEDURE

Basic Ignition System Checks (C4): C(3)I: Spark

Disconnect tachometer wire (if equipped). A shorted tachometer will not allow vehicle to start. Disconnect cam sensor and attempt to start engine. If engine starts, see cam sensor trouble code in TESTS W/CODES article.

Check for adequate spark with Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.

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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