Chevrolet Silverado / GMC Sierra. Service manual — part 1226

BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS - USING
OSCILLOSCOPE PATTERNS

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

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

2008 Chevrolet Silverado 1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

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

Spark plugs fouled

Replace spark plugs

2008 Chevrolet Silverado 1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING

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

2008 Chevrolet Silverado 1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

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

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

2008 Chevrolet Silverado 1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures