New guy here. I have done some searching but would like some clarifications on some questions.

First off I own a 98 Accord 4cyl. with 97k miles. My CEL has been on for about 4 months now (owned the car for 11 months) and barely got some consistent readings with the code. The previous times the CEL came on it was not specific on what the error was (I was told that it happens sometimes...) Anyways I threw a low efficiency code for the cat and I would like to replace it.

My first question is; what is the exact part number for the aftermarket MagnaFlow High Flow cat? I went to http://www.andysautosport.com/...aflow/ and found a bunch of different versions. From looking at the existing unit it seems like the pipe is 2-1/4" inlet/outlet? Is this correct?

My general question would be is this my best bet as far as price is concerned? I will install it myself. I am not sure if it needs to be welded but from some of the other threads I think I might, which is not a problem for me.

I was a little confused after searching the forum, I read some replies about how it might be the secondary 02 sensor since I'm not experiencing any drawbacks to a dead cat. I have been getting poor gas mileage lately (~26) is what makes me suspect the cat is starting to go.

Any help that you could offer would be greatly appreciated. TIA

 

Sometimes the trouble code is just a symptom of the real problem, so keep that in mind.

Primary O2 sensor controls the air fuel ratio. The cat converts the combustion byproducts into other less harmful gasses.

Poorly functioning O2 sensors will have an effect on your your mileage, but the main culprit would be the primary O2 sensor. The secondary senses cat efficiency and as far as I know does not have an immediate effect on the air/fuel ratio.

Sorry I can't be of more help, but I don't have specific experience with your situation.

 

Thanks for the reply. I had a feeling about the primary as well because of the fuel milage. I won't be a happy man if I replace the cat to only find myself in the same situation.

 

ya it would be cheaper to swap out the o2 sensor rather that the cat conv first

 

It would be cheaper but is it necessary? I have nothing to convince me right now that the primary 02 is bad. I believe it would be the cat since thats the code I got. Is it common for these cats to go out around 100k miles?

Anybody have that Magnaflow unit that can give me a part number or their thoughts?

 

The cat on my '99 Accord went bad about 10,000 miles ago. (I've got over 170,000 miles on the car now.) I replaced it with a Magnaflow high-flow cat because it was the cheapest route available to me. (The shop had the cat in stock, so I don't know the part #.)

Although my butt-dyno says I gained a good amount on the top end, I also lost a good deal of low-end power. Of course, I expected this, but maybe not quite this much. For daily driving, it doesn't really bother me. I've noticed that I've lost maybe 1 mpg during city driving, but highway driving is still the same. I rarely punch the gas from a stop, but when I do I miss the torque that I lost. I mean, the car IS heavy...

Oh, and if you have an exhaust on the car, it's going to get a hell of a lot louder. If you have a stock exhaust you probably won't notice a difference.

In regards to your secondary O2 sensor, which is the one that is used to monitor the cat, it can be tested with a multimeter to see if it's still okay. Generally a bad secondary O2 will throw a different code than a bad cat, but not always. Although I never noticed a drop in mpg when my cat went bad, reliable sources from this forum say that is definitely possible.

Hope this helps...

 

Interesting to know that the Magnaflow cat will loose bottom end. I wasnt aware of this. My Accord is soley a DD, and is 100% stock. So I feel that this will not be an issue.

I'm now concerned about my loos in mpg. I was getting about 29 with my driving style, and now it seems to be barely making 26. I replaced the plugs, wires, air-filter, belt, and ALL fluids about 10k miles ago.

I was also thinking about getting a short ram intake or a K&N drop in to help with milage, but it seems from searching this forum that it doesnt help at all. With my other vehicles there was a bump in mpg.

Thanks for the replies, keep 'em coming.

 

There will be a bump in mpg by swapping to a higher flowing air filter, but the common problem is people put an intake on and then run around with a heavy foot and it causes the gas mileage to diminish. It is not because of the intake.