Engine Control System & Fuel System - 4.2L - Diagnosis & Troubleshooting: Backfire

Backfire

Inspections	Action
Definition: The fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Preliminary	Refer to Symptoms - Engine Controls .
Ignition System	Inspect the ignition system.
Engine Mechanical	Inspect the engine for the following the items: Engine compression - Refer to Engine Compression Test . Improper valve timing Manifold gaskets Sticking or leaking valves Inspect the intake and exhaust system for fresh air entering the exhaust upstream of the catalytic converter or restrictions. Refer to Symptoms - Engine Exhaust .
Fuel System	Inspect the fuel system. Refer to Fuel System Diagnosis . Perform the fuel injector balance test. Refer to Fuel Injector Diagnosis (w/J39021 or Tech 2) or Fuel Injector Diagnosis (w/CH47976) .