On my Mitsubishi shogun sport van 2002 3.0L V6, There was a slight misfire on cylinder 5. We replaced spark plugs, all the HT leads (Ignition wires) and Ignition coils (all 3). That didn't solve our issue so we checked for compression and it was all normal and every cylinder was the same so then we replaced all the fuel injectors and it still hasn't solved the misfire. It use to pop up as an error code but doesn't anymore and doesn't show up with any engine lights. It seems to start backfiring longer the car has been running/Idling (backfires more as the engine gets hot) We are thinking the electrics deeper in the car? Please help.
Try searching for Mitsubishi forums with owners, techs and mechanics familiar with your model. There's always someone with more knowledge, experience and skills in specific forums as a way to use the internet message boards of sharing free info instead of relying on dealer or repair shops.
Misfiring may be more complicated if it wasn't fixed with plugs, wires, ignition coils and compression checks (for mechanical health). The EFI system may be the next steps in diagnosing this misfire issue. Fuel pressure was mentioned to check. Fuel filter may need replacing at recommended mileage intervals. The EFI system can be complicated to the average diyer unless familiar with sensors, their operation and how they contribute to the ecm running the EFI system. Diagnosing worn or faulty sensors can be difficult without more than average knowledge of issuing scantools, readers and interpreting sensor outputs.