Troubleshoot ignition system, no-start, engine runs rough, etc.

General Automotive Repair

Before trouble shooting or diagnosing an electronic ignition system, ensure that all wiring is connected properly between distributor, wiring connector and spark plugs. Ignition problem will show up either as: Engine Will Not Start or Engine Runs Rough.

Engine Won't Start

• Open circuit between distributor and bulkhead connector: Repair circuit
• Open circuit between bulkhead connector and ignition switch: Repair circuit
• Open circuit between ignition switch and starter solenoid: Repair circuit

Engine Runs Rough

• Fuel lines leaking or clogged: Tighten fitting, remove restriction
• Initial timing incorrect: Reset ignition timing
• Centrifugal advance malfunction: Repair distributor advance
• Defective spark plugs or wiring: Replace plugs or plug wiring

Component Failure

• Spark arc-over on cap, rotor or coil: Replace cap, rotor or or coil
• Defective pick-up coil: Replace pick-up coil
• Defective ignition coil: Replace ignition coil
• Defective vacuum unit: Replace vacuum unit
• Defective control module: Replace control module

USING OSCILLOSCOPE PATTERNS

Firing Voltage Lines are the Same, but Abnormally High

• Retarded ignition timing: Reset ignition timing
• Fuel mixture too lean: Readjust carburetor
• High resistance in coil wire: Replace coil wire
• Corrosion in coil tower terminal: Clean and/or replace coil
• Corrosion in distributor coil terminal: Clean and/or replace distributor cap

Firing Voltage Lines are the Same but Abnormally Low

• Fuel mixture too rich: Readjust carburetor
• Breaks in coil wire causing arcing: Replace coil wire
• Cracked coil tower causing arcing: Replace coil
• Low coil output: Replace coil
• Low engine compression: Determine cause and repair

One or More, But Not All Firing Voltage Lines are Higher Than Others

• Carburetor idle mixture not balanced: Readjust carburetor
• EGR valve stuck open: Clean and/or replace valve
• High resistance in spark plug wires: Replace spark plug wires
• Cracked or broken spark plug insulator: Replace spark plugs
• Intake vacuum leak: Repair leak
• Defective spark plugs: Replace spark plugs
• Corroded spark plug terminals: Replace spark plugs

One or More, But Not All Firing Voltage Lines Are Lower Than Others

• Curb idle mixture not balanced: Readjust carburetor
• Breaks in plug wires: Replace plug wires causing arcing
• Cracked coil tower causing arcing: Replace coil
• Low compression: Determine cause and repair
• Defective spark plugs: Replace spark plugs
• Corroded spark plugs: Replace spark plugs

Cylinders Not Firing

• Cracked distributor cap terminals: Replace distributor cap
• Shorted spark plug wire: Determine cause and repair
• Mechanical problem in engine: Determine cause and repair
• Defective spark plugs: Replace spark plugs
• Spark plugs fouled: Replace spark plugs

General Automotive Repair

---