Backfires

Definition: Fuel ignites in intake manifold, or exhaust system, making a loud popping noise.


^ Perform "Diagnostic Circuit Check - Calif."


^ Perform "System Performance Check - Calif."


^ Visual (Physical) Check:


- Vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label.


- Ignition wires for cracking or hardness proper connection, at both the distributor cap and spark plugs.


- Chaffed wiring harness by pulleys or metal edges.


^ Make sure hot air tube is connected to air cleaner.


^ Check proper operation of THERMAC.


^ Note: Cold engine only - check the following for sticking or faulty operation:

- Carburetor choke, including vacuum break and throttle linkage. Check choke TVS if used.

- Check EFE Electric Heater - see Chart C-9.

^ Check carburetor accelerator pump operation.
^ Check vacuum sensor hose for restriction, or for fuel or water in hose.


^ Check for proper operation of EGR valve.


^ Perform a compression check - look for sticking or leaking valves.


^ Check for restricted exhaust system, See Restricted Exhaust System Check.


^ Check output voltage of ignition coil. See Chart C-4A.


^ Check operation of decel (gulp) valve if so equipped.


^ Check for crossfire between spark plugs, distributor cap, spark plug wires and proper routing of plug wires. Wires for cylinders which fire in sequence on the same side of the engine should not be routed next to each other; i.e., 8 and 4, and 5 and 7.


^ Check for intermittent condition in ignition system.


- Pick-up coil


- EST wire (to ECM Terminal 12)


- Ignition coil ground on integral coil


- Ignition coil primary connections


^ Check for proper valve timing.