Backfire

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

PRELIMINARY CHECKS
Perform the visual and physical checks as described in Preliminary Checks. - Important Preliminary Checks

IGNITION SYSTEM
CHECK:

- Proper ignition coil output voltage with spark tester J26792 (ST 125).
- Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
- Ignition wires for crossfire. Also inspect distributor cap, ignition wires, and distributor vent system. Refer to Diagnostic Charts / C-Charts/ Distributor Ignition System Check. Testing and Inspection

ENGINE MECHANICAL
CHECK:

- Compression, valve timing, manifold gaskets, sticking or leaking valves.
- EGR gasket for faulty or loose fit.
- EGR operation (EGR valve open all the time).
- Intake and exhaust manifold for casting flash.