If it is petrol then it is probably the ignition timing not set correctly.
If it is diesel then it is probably the injection pump timing not set correctly
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.
Either the timing is excessively retarded or you have a worn camshaft or related problem.
is this truck is a good truck i like to know if this truck is a good truck what is wrong with this truck
Backfiring is caused by incorrect timing, or plug wires installed incorrectly which messes up the firing order. Make sure your plug wires are installed correctly. Can also be caused by an overly rich fuel air mixture.
Intake manifold gasket may be leaking - check for loose bolts or replace fasket.
Sounds like the timing is off or you have the plug wires connected wrong. Click the link I will post.
Propane backfiring in a Ford truck could be due to a fuel mixture issue, such as an incorrect air-to-fuel ratio, or a problem with the timing in the engine. It could also be caused by a malfunctioning spark plug or an issue with the fuel injection system. A thorough inspection by a mechanic would be needed to diagnose and fix the specific cause of the backfiring.
More than likely it is out of time. Have the timing checked. If you have changed the plugs or plug wires, you have them hooked up wrong.
Never mind thanks anyway turned out to be a bad CTS
sounds like the tineing belt.
what is wrong when the truck just turn over and want start.
The truck not getting the right amount of fuel if it back fires when its accelerating check to see if all your fuel injectors are good.