Hummer H2. Manual - part 30

BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS 

BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS - USING OSCILLOSCOPE 
PATTERNS 

combustion 

Improper gapping procedure 

Re-gap spark plugs 

Rust Colored Deposits 

Additives in unleaded fuel 

Try different fuel brand 

Water In Combustion Chamber 

Blown head gasket or cracked head 

Repair or replace head or head gasket 

NOTE:

Before 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. 

CONDITION & POSSIBLE CAUSE 

CORRECTION 

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 see ENGINE 

PERFORMANCE 

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 

CONDITION & POSSIBLE 
CAUSE 

CORRECTION 

Firing Voltage Lines are the Same, but Abnormally High 

Retarded ignition timing 

Reset ignition timing, see ENGINE 

PERFORMANCE section 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

Fuel mixture too lean 

Readjust carburetor, see ENGINE 

PERFORMANCE 

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, see ENGINE 

PERFORMANCE 

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, see ENGINE 

PERFORMANCE 

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, see ENGINE 

PERFORMANCE 

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 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING 

Spark plugs fouled 

Replace spark plugs 

CONDITION & POSSIBLE 
CAUSE 

CORRECTION 

Hard Starting 

Binding carburetor linkage 

Eliminate binding 

Binding choke linkage 

Eliminate binding 

Binding choke piston 

Eliminate binding 

Restricted choke vacuum 

Check vacuum lines for blockage 

Worn or dirty needle valve and seat Clean carburetor, see ENGINE PERFORMANCE 

Float sticking 

Readjust or replace float see the ENGINE 

PERFORMANCE section 

Incorrect choke adjustment 

Reset choke adjustment see ENGINE 

PERFORMANCE 

Defective coil 

Replace coil 

Improper spark plug gap 

Regap spark plugs 

Incorrect ignition timing 

Reset ignition timing see ENGINE 

PERFORMANCE 

Detonation 

Over-advanced ignition timing 

Reset ignition timing see ENGINE 

PERFORMANCE 

Defective spark plugs 

Replace spark plugs 

Fuel lines clogged 

Clean fuel lines 

EGR system malfunction 

Check and repair EGR system 

PCV system malfunction 

Repair PCV system 

Vacuum leaks 

Check and repair vacuum system 

Loose fan belts 

Tighten or replace fan belts, see ENGINE 

PERFORMANCE 

Restricted airflow 

Remove restriction 

Vacuum advance malfunction 

Check distributor operation 

Dieseling 

Binding carburetor linkage 

Eliminate binding 

Binding throttle linkage 

Eliminate blinding 

Binding choke linkage or fast idle 
cam 

Eliminate binding 

Defective idle solenoid 

Replace idle solenoid see ENGINE 

PERFORMANCE 

Improper base idle speed 

Reset idle speed, see see ENGINE 

PERFORMANCE 

Incorrect ignition timing 

Reset ignition timing see ENGINE 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

PERFORMANCE 

Incorrect idle mixture setting 

Reset idle mixture, see ENGINE 

PERFORMANCE 

Faulty Acceleration 

Incorrect ignition timing 

Reset ignition timing see ENGINE 

PERFORMANCE 

Engine cold and choke too lean 

Adjust choke and allow engine to warm-up 

Defective spark plugs 

Replace spark plugs 

Defective coil 

Replace coil 

Faulty Low Speed Operation 

Clogged idle transfer slots 

Clean idle transfer slots, see FUEL 

Restricted idle air bleeds and 
passages 

Disassemble and clean carburetor, see FUEL 

Clogged air cleaner 

Replace air filter 

Defective spark plugs 

Replace spark plugs 

Defective ignition wires 

Replace ignition wire see ENGINE 

PERFORMANCE 

Defective distributor cap 

Replace distributor cap 

Faulty High Speed Operation 

Incorrect ignition timing 

Reset ignition timing see ENGINE 

PERFORMANCE 

Defective distributor centrifugal 
advance 

Replace advance mechanism 

Defective distributor vacuum 
advance 

Replace advance unit 

Incorrect spark plugs or plug gap 

Check gap and/or replace spark plugs 

Faulty choke operation 

Check choke and repair as required 

Clogged vacuum passages 

Remove restrictions 

Improper size or clogged main jet 

Check jet size and clean, see FUEL 

Restricted air cleaner 

Check filter and replace as necessary 

Defective distributor cap, rotor or 
coil 

Replace cap, rotor or coil 

Misfire at All Speeds 

Defective spark plugs 

Replace spark plugs 

Defective spark plug wires 

Replace spark plug wires 

Defective distributor cap, rotor, or 
coil 

Replace cap, rotor, or coil 

Cracked or broken vacuum hoses 

Replace vacuum hoses 

Vacuum leaks 

Repair vacuum leaks 

Fuel lines clogged 

Remove restriction 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures