Backfires

SYMPTOM DESCRIPTION:
Fuel ignites in intake manifold, or in exhaust system, making a loud popping noise.



SYSTEM OR COMPONENT TO CHECK ACTION

IGNITION
CHECK: - IGNITION COIL.
Verify output voltage is correct
using a spark tester or equivalent.
- SPARK PLUGS.
Remove spark plugs,
check for fuel fouled plugs, cracks, wear,
improper gap, burned electrodes, or
heavy deposits. Replace as necessary.
- SECONDARY CIRCUIT.
Check for crossfire between the
spark plugs, spark plug wires
and within the distributor cap.
Verify spark plug wires are routed correctly.
- IGNITION TIMING
Verify timing is set to specifications



ENGINE CHECK: - COMPRESSION.
Perform a compression check,
look for sticking or leaking valves.
- VACUUM LEAKS.
Intake manifold gasket and
hoses.
- RESTRICTIONS.
Intake and exhaust system for
casting flash or other restrictions.

- CAMSHAFT
Check for flatness of lobes.





EMISSIONS CHECK: - AIR INJECTION.
Faulty check valve, diverter valve
and hoses.
- EGR Valve
For being open all the time.