Rep Power: 266

Ok a couple of weeks ago i installed a hi flo cat on my vic. before that i was gettin an average of 32 mpg. lately ive been gettin around 28, and last tank was as low as 26. yes the check engine light is on, and i figured from the start it was something to do with the o2 sensor. but would it be a bad o2 sensor? or does it have something to do with the hi flo cat? I tried resetting the ecu, and that worked for about 5 seconds.

btw: i did read the engine light sticky first, and it didnt really help me with my question

 
Rep Power: 453

you obviosuly didnt read the right one.

http://www.7thgencivic.com/forums/sh...d.php?t=233373

are both 02 sensors still hooked up?

 
Rep Power: 266

yeah they are both hooked up. im almost ceratin its runnin rich, but the car still runs fine, no black smoke or anything

 
Rep Power: 453

well then you need to find out what code its throwing and diagnosis it. Dont assume its a o2 sensor issue. Now My first guess is its because of your high flow cat. Alot of them are just downpipes with a resonator and dont actually have the catylst material in it. All a high flow cat is is a regular cat converter with a bigger inlet and outlet. Now if you do have an actual cat converter, then get the code read. But if you dont, then the code is on because the rear o2 sensor is signaling the ECU that there is a failure with the cat.

 
Rep Power: 266

hmm ok. ill get it checked after the new year. but would the cat failure signal cause it to pump more feul like its doing?

 
Rep Power: 302

Probably, because the reason it runs rich to begin with is to light up the cat. Normally, once the cat lights, the ecu then balances the air/fuel ratio to keep the cat at it's optimum burning point. There is a fancy name for this that I can't pronounce, much less spell, sorry.

If the ecu senses no difference between the front and back O2 sensor, it thinks the cat has not lit, so it's not doing it's job. THe ecu runs richer to try to light the cat, but after a while it will time out and throw a code. A good cat lights in a very short time, so the ecu has a built in time delay for this before it throws a code.

 
Rep Power: 266

hmmm ok. makes sense, although it threw the check engine light nearly immediately

 
Rep Power: 302

Takes only seconds to light a modern cat. But, it could also be a different sensor....

A simple code scanner is about $30. Google for it. I got one shipped for like $38. Worth having.

Did you do the idle relearn, btw? Oh, and did you check that both O2 sensors are still plugged in?

 
Rep Power: 266

yeah, both o2s are plugged in, and i did the relearn. it came back on after about 5 seconds of runnin the car after i did the reset.

are the code scanners vehicle specific? or is it universal to all cars with obd2?

 
Rep Power: 453

No code scanners arent vehicle specific. Any OBD II scanner will work. As long as the vehicle has an OBD II system. some cars, however, require that only the manufacture be able to clear codes. the civic isnt included in that.

 
Rep Power: 319

Basically any car made after '96 has an OBDII. Does any manufacture still have specific one? I thought they got rid of that.

 
Rep Power: 302

This ebay tool works fine, ( item 4598427552 ) I have one. Clears codes too.

 
Rep Power: 0

My friend James has the ebay version. He uses it and he actually swears by it. Of course thats no guarantee, but you get the point.

 
Rep Power: 319

You know your MPG often drop in cold weather. My truck went from 18-20 to 14-16ish MPG. But I also use 4x4 more often in the winter, so that makes a big difference. My finace's '06 civic went down to, form about 31-33 MPG to 28-29.

 
Rep Power: 278

Yup, jus checked mines yesterday, and it went from 32mpg to 28mpg.

 
Rep Power: 453

I dont remember which one it was, it might have been lexus, but after we did a intake cleaning on it, the check engine light came on (they usually do after the cleaning) and when we tried to clear it, it wouldnt respond with the scanner. We even tired 3 different ones and it wouldnt respond. I was then told that it would go off by itself or the dealer would have to clear it.

But yes most cars after 96 are OBD II. I think, however, some of the higher end cars have the OBD III systems.

 
Rep Power: 266

Now that i didnt know. It was much colder than it had been last week.