2004 Chrysler Town & Country P0305 Misfire: Emissions Failure Due to Cylinder Compression Issue

The P0305 misfire is indeed an emissions-related issue, as misfires contribute to higher hydrocarbon emissions. Cylinder 5 (driver's side rear bank) is the affected cylinder — this location makes servicing less convenient. To diagnose properly: remove the spark plug from cylinder 5 and inspect it for wetness, dryness, black or tan deposits. This helps determine if there’s a fuel delivery or combustion issue. Since the root cause of low compression (only 70 psi) is unclear, consider a targeted remedy as a last resort: - With the spark plug removed, add either GM Part Number 12378549 or Chrysler Part Number 04318001AB* to the cylinder. - This engine cleaner helps address potential stuck rings caused by carbon buildup. - After adding the cleaner, spin over the engine without the plug in place for a few seconds to allow any residual fluid to escape — this may be messy but is worth attempting. Afterward, reinstall the spark plug and continue driving. Monitor for improvement. *Note: These are engine-specific carbon cleaners designed to help with sticky ring conditions. PS: The $400 emissions waiver fee might not be necessary. Items like tire maintenance, oil changes, air filter replacement, or previous work done may qualify for credit under some programs — check with the inspection station directly.