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 EGR Valve for being open all the time.