Engine Backfires

If fuel ignites in intake manifold or exhaust system and makes a loud popping noise, check the following items:

• Perform VISUAL/PHYSICAL INSPECTION .
• Ensure sufficient secondary spark is available.
• Check for faulty spark plugs, spark plug wires, distributor cap and rotor causing crossfire between spark plugs.
• Ensure ignition timing and controls are working properly.
• Check for proper spark plug wire routing.
• Check for faulty hydraulic lifters, broken or weak valve springs, sticking or leaking valves, low compression, incorrect valve timing, or incorrect or worn camshaft.
• Check EGR (open all the time) and solenoid operation.
• Check intake and exhaust manifolds for casting flash.
• Check EGR valve for being open all the time.