I have a 2004 Mazda 3 with a 2.0. Approx. 3 months ago it would not start. It turned over but wouldn't fire. I replaced the fuel pump and it started right up and ran fine for 3 days. Then it left my son stranded about 3 miles from the house where he said it just wouldn't go and died. I went and started it and it sputtered home barely. Could barely give it gas. It sputtered from the engine area and not really from the back exhaust. I started thinking it was possibly a O2 sensor or the catalytic converter. I replaced both o2 sensors and it didn't help. I replaced the Front Catalytic converter that has the header pipes attached and it seemed ok briefly during the test drive then it started sputtering again. When it sputters and you give it gas it just boggs down and you have to let off the gas then lightly press it to make it want to go. I still have a back catalytic converter (I think), that would require me removing the whole back exhaust system because a new rear converter would need to be welded in. But is this even the problem? It threw a code initially before I replaced the fuel pump and it was a fuel sending sensor. But its not throwing any codes now and it runs like crap. The sputtering comes from the front in the engine area. Its like the exhaust is clogged which is why I replaced that front converter. But the last thing I want to do is put more $ in it in replacing the back converter and still have the problem. IF YOU HAVE ANY IDEAS OR SUGGESTIONS I WOULD REALLY APPRECIATE IT. The car's been sitting for almost 3 months and I miss driving it. Thanks.