Backfire

DEFINITION
Fuel ignites its Intake Manifold, or in exhaust system, making loud popping noise.

PRELIMINARY CHECKS
Perform the careful Visual/Physical Checks as described in Preliminary Checks. Preliminary Checks

IGNITION SYSTEM
CHECK: Proper Ignition Coil output voltage with Spark Tester J26792 or equivalent (ST-125).
CHECK: Spark plugs. Remove Spark Plugs, check for wet Plugs, cracks, wear, improper gap, burned Electrodes, or heavy deposits. Repair or replace as necessary.
CHECK: Spark Plug Wires for crossfire, also inspect Electronic Ignition, Spark Plug Wires, and proper routing of Plug Wires.
CHECK: Ignition Timing. Refer to "Vehicle Emission Control Information" label.
CHECK: If an Intermittent condition exists in the Ignition System, see Diagnostic Charts / Chart C-4. C - Charts

ENGINE MECHANICAL
CHECK: Compression, look for sticking or leaking Valves.
CHECK: Valve Timing.
CHECK: Intake and Exhaust Manifold Passages for casting flash.

FUEL SYSTEM
CHECK: Perform Fuel System Diagnosis Check, see Diagnostic Charts / Chart A-7. A-7: Fuel System Diagnosis

ADDITIONAL CHECKS
CHECK: Exhaust Gas Recirculation (EGR) Gasket for faulty or loose fit.

CHECK: EGR operation for being open all the time. Refer to Diagnostic Charts / Chart C-7. Chart C-7A: EGR System Check

CHECK: Intake and Exhaust Manifold for casting flash.