Hello everyone. This is my first post. I currently am experiencing a misfire with my truck. It only does it at cruising speeds on the highway. Around 50-70mph, and about 2000rpm. The truck also is giving me the code P0420. I know that is the catalytic converter bank 1. I think the misfire is causing the code. Any ideas on what could cause the misfire. I changed the plugs (ac delco platinum), wires, cap, and rotor. I am just trying to get some ideas before I end up taking it to the shop. I would rather fix it myself, if possible. It is a 4.3 vortec with 102k. Thanks and have a good day.

 

run a compression test to see if you have a cylinder goin down. would also probably replace the cat.

 

Thanks for the reply. The truck also has an exhaust leak that I havent looked at yet. Could a misfire be caused by an exhaust leak, I know it can cause the p0420 code if it is in front of the cat. I will probably take it to the dealership soon and have it tested. Bye the way it is still getting 20mpg with the misfire.

 

Well, I took it to the dealership today. They said it is a clogged catalytic converter. Would that cause a misfire at around 2k rpm and up?