If you're experiencing a misfire on cylinders 3 and 5 of your GMC Acadia 2010, even after replacing the spark plugs and ignition coils, there are a few other potential issues that you might want to investigate:
Fuel injectors
A clogged or malfunctioning fuel injector could lead to a misfire. Inspect the fuel injectors on cylinders 3 and 5 for any signs of blockage or malfunction.
Compression issues
Low compression in cylinders 3 and 5 can also cause misfires. Perform a compression test to check the compression levels in those cylinders.
Ignition system
While you mentioned that you replaced the spark plugs and ignition coils, double-check the installation to ensure they are correctly seated and the connections are secure.
Wiring and connectors
Faulty wiring or connectors could disrupt the flow of electricity to the spark plugs and cause misfires. Check the wiring and connectors related to cylinders 3 and 5.
Engine control module (ECM)
The ECM controls the ignition timing and fuel delivery. If it's malfunctioning, it may not be delivering the right signals to the ignition system. You might need to have the ECM scanned for any error codes.
Vacuum leaks
Unmetered air entering the intake system due to vacuum leaks can cause misfires. Check for any leaks in the intake manifold or vacuum hoses.
Mechanical issues
Other mechanical problems, such as a worn camshaft or valve train issues, could also contribute to misfires. A thorough inspection of the engine might be necessary.
If you've ruled out all the above possibilities and the misfire persists, it's advisable to have the vehicle diagnosed by a professional with proper diagnostic equipment.
