Backfires

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



PRELIMINARY CHECKS

^ Perform the careful visualiphysical checks as described in "Preliminary Checks."

IGNITION SYSTEM

^ CHECK: For proper ignition coil output voltage with spark tester J 26792 (ST-125) or equivalent.

^ CHECK: 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, see "Electronic Ignition (EI) System."

ENGINE MECHANICAL

^ CHECK: Compression - Look for sticking or leaking valves.
^ CHECK: Valve timing.
^ CHECK: Intake manifold passages for vacuum leaks.

FUEL SYSTEM

^ CHECK: Perform fuel system diagnosis check, see CHART A-7. Related Tests, Information and Procedures
^ CHECK: Fuel injectors. Perform "Injector Balance Test," refer to CHART C-2A. Part 3 of 3 (Fuel Injector Balance Test)

ADDITIONAL CHECKS

^ CHECK: EGR gasket for faulty or loose flt.
^ CHECK: EGR operation (EGR valve open all the time)- Refer to "Exhaust Gas Recirculation (EGR)," CHART C-7. Chart C-7 EGR System Check
^ CHECK: Intake and exhaust manifold for casting flash.