Hey guys, I know it's one of my first posts here but trust me I'm not here to just get help and go...this forums seems like a home so far
Anyways, I have a d16y8 in my 00 civic, After installing a test pipe in it about 1.5 years ago the CEL went immediately on (which is odd, i thought it takes time). Later on of course it's due to bad catalyst, so I go on for a bit before installing a hi-flow one instead, problem not fixed. I then relocate the sensor farther back to work like an oxygen simulator, didn't do the trick. I figured bad sensor so i replaced it. For a bit it was fine but the CEL came back on for "Bad fuel mixture" and then about 2 weeks later it's also on for the stupid catalyst again.
Not quite sure what to do here.

I smell burning oil at higher rpms so im figuring it's a bad head gasket or piston rings but i'm really lost at what to do...any suggestions?
I'm going to work on it thursday with a friend and need to know all possibilities, i'll post day after day as it goes on with pics of course!

 

What specific CEL codes are currently being thrown?

Have you checked for an exhaust leak? Has oil leaked onto the O2 sensor(s)?

 

There are actually a few exhaust leaks, not due to gasket problems but i think the aftermarket header, with the hi flow cat then stock catback just do not want to fit together correctly.
As for oil leaking into the 02 sensors i'm not 100% sure, there does seem to be an oil leak problem though, the oil pan under the car appears to be a bit oily so i'm thinking there might also be a bad oil pan gasket.
And which 02 sensors do you mean for the oil leak

 

The exhaust system leak could cause a CEL code for the catalytic converter.

What specific CEL codes are currently being thrown?

 

what I have done was get those two wires together under the passenger side to make the CEL light blink in correspondance to numbers.
It came out as 45 and i believe 67
I can't find the original list though, i believe i got it off of superhonda somewhere

 

Code 67 is for a bad cat or an exhaust leak.

Code 45 indicates system too lean (P0171) or rich (P0172) (see picture for possible causes). Take your car to AutoZone and they will tell you whether the code is for too lean or too rich. As you can see, a system too lean code can also be caused by an exhaust leak, or possibly a bad primary O2 sensor (defective or oil contaminated). Other causes are also possible.

I hope this helps.

 

you have no damn idea how much this helps, ill find out about too rich or too lean asap

 

got it checked today

somewhat, they hooked up the computer to it at advance auto

anyways, errors were

system mixture too LEAN (not rich wtf)

and

02 sensor circuit malfunction
(so i might not have bad emissions, but circuit, guy said the pin could be out...hmmm)

then possible diagnoses were
malfunctioning fuel trim
and
ignition system

 

What specific O2 sensor code was retrieved?

Given that the CEL code for a bad cat did not repeat, you may want to clear the ECU and determine whether the CEL again lights. If so, as is likely, then again retrieve the code(s) to find out if they are the same ones you just retrieved. The idea here is that you only want to initiate repairs if the CEL code is reproducible.

 

The thing is that I have reset the ECU a few times before
about 5 or so, then the light comes back on b/w 26 and 41 miles into driving

Also, twice the CEL has gone off seemingly on it's own after pumping gas to a full tank...but only twice