Hey all you Mustang enthusiasts. Been a while since I have been here but I need some advice here. I have a 99 Mustang and I have been told that the Cats are clogged therefore the car can't breathe, hence horrible gas mileage. I have been told I can do one of three things: 1. Replace all four cats, 2. Install a flowthrough exhaust or 3. just install straight pipes to the mufflers. I am trying to go the cheapest route possible, but still remain legal too. It is also throwing these two codes P0455 & P0301. Any suggestions?

 

P0455 - EVAP Emissions Controls. First, check your gas cap. Second, a bad gromet might cause this. You have a fuel leak somewhere.

P0301 - MIsfire on Cylinder 1. This could be a bad spark plug, bad spark wire, or bad ignition coil. All of these are fairly cheap. If its not one of these, there's a more serious engine problem, but its usually one of these. Start there.

Sadly, none of these codes are related to your CATS. You need to have CATS in your car for it to be legal, so any option that deletes them isn't legal. I would say replace the originals. Keeps it legal, and simple, especially if you're not looking to race.

 

http://www.obd-codes.com/p0455
http://www.obd-codes.com/P0301

As Cristina mentioned, those codes have nothing to do with your cats and if you remove them you will no longer be legal. Whomever told you your problem was your cats doesn't know what he/she is talking about. If your cat was so clogged to cause a drivability problem it would throw a code specific to the cat. There are also various ways to test a cat to see if it is clogged up or burned out. I would verify your cat is bad before going through the expensive of replacing them.

Your poor gas milage is probably due to the misfire.