Backfires

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

PRELIMINARY CHECKS
Perform the careful visual / physical checks as described in Preliminary Checks.

IGNITION SYSTEM CHECKS
^ Proper ignition coil output voltage with spark tester J 26792 (ST 125) or equivalent.
^ Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.

NOTICE: If an intermittent condition exists in the ignition system, refer to Ignition System.

ENGINE MECHANICAL CHECKS
^ Compression Look for sticking or leaking valves.
^ Valve timing.
^ Intake manifold passages for vacuum leaks.

FUEL SYSTEM CHECKS
^ Perform fuel system diagnosis check, refer to Chart A-7.
Related Tests, Information and Procedures

^ Fuel injectors, Perform injector balance test, refer to Chart C-2A.
Part 3 of 3 (Fuel Injector Balance Test)

ADDITIONAL CHECKS
^ Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.
^ EGR operation (EGR valve open at the time). See Chart C-7. Chart C-7 EGR System Check

^ Intake and exhaust manifold for casting flash.