LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> GMC >> 1990 >> Forward Control 3.9 L >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Basic Testing >> Basic Ignition System Checks (Gasoline) >> Spark
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Basic Ignition System Checks (Gasoline): Spark

  1. If factory tachometer is connected to ignition coil tachometer terminal, disconnect it before performing tests. When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.
  2. Using Spark Tester (ST-125), check for spark at coil wire (if applicable) and at each spark plug wire using spark tester. Check spark plug wire resistance on suspect wires. Resistance should be no greater than 30,000 ohms.
scientia non olet · About LEMON Manuals