Ok so I just bought some new exhaust for my coupe, I did full header back bisimoto manifold, magnaflow cat, greddy catback and now it's throwing a cel for the cat but it's brand new, I also replaced the o2 sensor but yet still throwing the cel. I went to advanced and had them run the obd2 cel reader and that's what it read. So confused, any help please and thank you!!

 

Does your new system have a spot for the secondary (downstream) o2 sensor?

Or do you have a primary o2 installed typically on the header.

There are 2 o2's

 

2, the one in the header and the one on the cat which is the one I replaced.

 

Bump

 

Don't bump every hour.
Sure you don't have any exhaust leaks?

 

What type of cat did you install, you need a 3 way cat by the way.

 

No leaks, I double checked and double checked again.

I got a brand new magnaflow cat.

 

Did you get a code before the exhaust?

Did you reset it to see if it comes back?

Are the headers off road only?

 

Yes, I had a code for it before the exhaust. When I was first gonna do exhaust I was gonna keep the oem cat but when the cel came on for the cat I decided to go on and replace it.

Yes I reset it, stayed off for about a day and came back.

I'm not positive if the bisimoto header is off road, I'll look into it

Thanks!!

 

magnaflow cats only have 2 honeycombs in them. that mite be ur problem but idk. my stock cat is gutted.

 

I looked at magnflow's site and thet say they are compliant 49 state and there is one for CA.

Where do you live by the way?

 

Alabama, no emissions. Well my main relay fuse blew this morning. I replaced it and the code is cleared as of now, but we'll see if it comes back. I'll keep you posted.

 

Cel is back and it is for the cat.... Could this be something wrong with my ecu? Maybe wire harness?? This is so confusing/frustrating.

 

The cat was not installed backwards by any chance was it?

 

Theres no way, off the header is a donut gasket with 2 spring bolts and to the mid pipe is like a 3 bolt triangle thing.

 

possible your running rich that would cause the 2nd 02 to throw up a code for cat. Do you burn oil or have like an afc hooked up?

 

your secondary sensor has to be dead if its not the cat. either buy a new sensor or a simulator. u could also buy a new sensor and defouler plug to move the O2 from the exhaust main stream and not get much exhaust gases. they work for when the cat goes bad or ur running a test pipe. but ur sensor has to be good for it to work.

 

Everything is brand new, new headers, cat, exhaust, and both o2 sensors. I even went and replaced the new down stream o2 for another new one. Only thing I can think of is maybe that what hideinplanvew said and it is my fuel is to rich, im pretty sure it does not burn oil cause it doesn't blow smoke at all. I'm gonna hook up my friends air/fuel ratio guage and see if it's the fuel being to rich and causing this irritating problem.

 

Search for "spark plug fouler" and try that method. Btw what P code was it?

 

Clean all of your electrical grounds in your engine bay. With a multimeter, and a helms manual, measure the resistance of the electrical ground to the battery negative terminal. The Resistance should be less than .5 ohms, preferably 0 ohms. Anything higher than that can indicate dirty ground or damaged wiring. A weak ground could easily cause this problem.

 

Finally gone, thank you fleabag.

 

Thanks to all who posted!!