Okay here it goes; as most of you know the 6th gen dx has a cat connected to the manifold. When the header(4-2-1)was installed the cat/manifold were both removed from the vehicle and new o2 sensors were installed(primary in cylinder 4 port and secondary at the end of down pipe). CEL was active and car began to blow smoke. I reset the ecu and disconnected the battery. CEL went off but still blew smoke. Someone told me it was caused by a cylinder that was running rich(o2 sensor only collecting info from one cylinder and not all of them like in the original manifold). Another person told me it was because the cat was removed with manifold(no more cat) and the ecu was getting reading it did not recognize. My Q. is, does this car's ecu require a cat to run properly? Do I need to add a high flow cat and where do i install it and what kindor, do I need to take my car to a pro and have the ecu re-mapped? Does the second o2 go into the "new" cat or in the second port on the down pipe of the header? Anyone who has a header on a dx please let me know what you've done and if you had this smoke problem? THANKS EVERYONE

 

to pass emissions, a cat is required. you cannot tamper with an obdII ecu. no you don't need a high flow cat, just an oem or standard aftermarket cat will do. the primary o2 goes in the 'header', the secondary goes in the cat. many people use an o2 simulator. and when you reset the ecu, only the light goes away, nothing changes,the problem is still there.

 

Would a high flow cat be better than oem? And yes, the light went out but the problem still there. The o2 sensor(primary) was one that I wired in myself.I thought maybe that was the problem but whenI put my old cat/manifold back on, it stopped smoking. CEL still comes on every couple of months(engine code P0420, catalystbeyond thresholdsomething rather).

 

in what sense? performance or emissions? quality?

 

In all sense!!!! But, do you know what might be causing the smoke, cat., o2, rich/lean cylinder????? If it is my cylinder, how can it be fixed if Ican't mod. ecu settings?

 

well, a high flow will result in more horsepower, louder exhaust, but more emissions, and sometimes will not last as long as stock. as for the smoke, check your cel with a scanner. there's nothing with the ecu settings unless you somehow altered the ecu.

 

Does this new cat, bolt to the flange at the end of the down pipe? I ran a obd2 scan, that's how I know the engine code(p0420)and I know the code has to do with either the manifold or o2 sensor. What about this o2 simulator. Does this make it so the secondary sensor doesn't have to be installed into the cat?

 

Still looking for answers?????????????????????????????????

 

haha me too. cuz i have the same questionnnnnn

someone help us!

 

all right guys one more time What exactly do u need to know? if ur question is about u wanting new header on ur car but still want to pass inspection ur best bet is just to convert over to the EX exhuast system. From the header to the cat to the other cat to the resonator to the muffler.

if u want after market headers than u will need to buy the after market headers than buy a high flow cat. u might have to extended the cat sensor to the bottom of the car if its not already there. i knwo on the DC header it only has one opening for the o2 sensor there no opening for the cat sensor. u might have to extend it to the bottom of the car.

all the o2 sensor simulator will do is eliminate the check engine light thats it the problem will still be there.

EDIT: if u still need more help than just post ur question.