Backfires

Definition

The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.

Preliminary Checks

Refer to "Important Preliminary Checks." Testing and Inspection

Ignition System Checks

^ Check for the proper ignition coil output voltage with the spark tester J 26792 or equivalent.
^ Check the spark plugs for the following:
- Terminal screw - bent, loose (rotate and pull)
- Ceramic Insulator - cracks, tracking, deposits (red or black dust)
- Tip Insulator - cracks, tracking, deposits (oil, carbon, glazing, fuel additive), loose (rattles)
- Center electrode - loose (wiggles side to side)
- Platinum pads - missing, wear, gap size (too large or too small)
^ Check the ignition system and ignition timing.
^ Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of plug wires).

Engine Mechanical Check

^ Check the engine for the following:
- Compression
- Valve timing
- Manifold gaskets
- Sticking or leaking valves
^ Check the intake and exhaust system for casting flash or other restrictions.

Additional Check

Check the Exhaust Gas Recirculation (EGR) Valve for being open all the time.