Backfires

DEFINITION
Fuel ignites in intake manifold, or in exhaust system, making a loud popping noise.

POWERTRAIN SYSTEM CHECK
Perform Chart 1 Powertrain System Check. Chart 1 Powertrain System Check

IGNITION SYSTEM CHECKS
Perform Chart C-1 Ignition Control Performance Test. C Charts

Check especially for:

^ Spark Plug Wires
- crossfire between cylinders
- wrong firing order
^ Distributor grounding points clean and tight
^ Correct ignition timing
^ Distributor cap, rotor, brush and button for moisture, cracks, dust or carbon tracking
^ Worn or loose distributor shaft gear
^ Bent distributor shaft or worn distributor shaft bushing

FUEL SYSTEM CHECK
Perform Chart 6C-1 Fuel System Check. Chart 6C-1 Fuel System Check

Check especially for:

^ Fuel Quality
- low octane level
- contaminants
^ Low fuel pressure
^ Low flow rate injector

EXHAUST SYSTEM CHECKS
Perform Exhaust Diagnosis, looking in particular for:

^ Restricted catalytic converter or exhaust

MECHANICAL CAUSES
Check for the following mechanical causes:

^ Valves sticking in valve guides
^ Worn camshaft lobes
^ Broken/weak valve springs
^ Bent push rods
^ Worn rocker arms