backfiring.
Backfiring.
If it is backfiring only when you kill the engine, allow the engine to idle a few minutes before you kill it. If it is backfiring while in use, check the intake gasket and bolts for wear or looseness.
Could be a hole or leak at one of the joints or cylinder head bolts / nuts.
carb or timing
Backfiring is usually an indication of a lean condition. When it does it during cranking, it's probably timing related.
In a TBI engine, backfiring after warming up can be caused by issues like a lean air-fuel mixture, a failing fuel injector, a malfunctioning idle air control valve, or a vacuum leak. These can lead to incomplete combustion in the engine, resulting in backfiring through the throttle body. Regular maintenance and troubleshooting of these components can help resolve the issue.
Water in the gas can cause misfiring in an engine, leading to backfiring. When water is present in the fuel system, it can disrupt the combustion process by preventing the fuel from burning properly, resulting in backfiring as the engine tries to compensate for the imbalance. It is important to address any water contamination in the gas to prevent engine performance issues.
The year, make and model info would be helpful but a large vacuum leak could do that.
Your GMC truck may be backfiring due to several issues, such as a faulty ignition system, incorrect timing, or a rich air-fuel mixture. Other potential causes include a malfunctioning fuel injector or exhaust leaks. It's important to diagnose the problem accurately, as backfiring can lead to further engine damage if not addressed. Consulting a mechanic for a thorough inspection is recommended.
Spark plug wires crossed, Bad distributor cap and /or rotor, Exhaust leaks close to engine, Worn camshaft/lifters, Burned valve, Also need to know if it is backfiring out the tail pipe or out the carburetor, it makes a difference.
You either removed the catalytic converter or you are running too rich.