Hi. I have a 98 Civic LX (manual trans) with 192 000 miles on it. It was getting at least 37 mpg until my check engine light came on (Code P0420) for the cat converter. At that point the gas mileage was around 34 mpg. I took it in to confirm the cat converter problem and they found that I have a crack in my exhaust manifold and they replaced the converter. Since I got the car back, my gas mileage is even WORSE! I don't understand how this could be. I'm lucky if I get 32 mpg. I had a major tune-up done less than a year ago and had the timing belt replaced. Any idea what the problem could be? Is it something the mechanic did? The car also idles a bit rough.
Sounds like the reason you need it replaced is because it is plugged. I know, my 96 civic ex did the same thing. They are pricey, but I was adding a cat-back exhaust anyway and I just got a high flow converter. Any converter will be expensive, they really aren't cheap, I got mine for 175 and that was off e-bay. But beware of e-bay they sell stuff that doesn't work, or will throw a Check Engine Light. Just do some research, the internet is great for that, and you will be ok. I don't think your mechanic did anything, but since the O2 sensor in the rear is not getting any input, the computer might be dumping fuel in and richining the mixture which would cause a drop in fuel mileage.
February, 2, 2006 AT 5:29 PM
Many cat. Converters are replaced when the o2 sensor is the problem. Check the o2.