Do track pipes cause CEL?

[levis76]

I have a 98 Legacy 2.5L GT w/ 4EAT. If I replace my stock header and cat pipe with an EL header and a 2.25" catless track pipe that has bungs for both the O2 sensors, will this setup cause any CELs? I guess my question is how does the ECU use the signals sent by the O2 sensors? Are they compared with one another or are they both used individually to adjust the fuel/air ratio? One last question, what size bolts do I need for the header flanges? The header I am buying doesn't come with new hardware and I want to replace the studs and nuts as they are very corroded.

[sexystover]

it will cause a cel, and make sure you heat the heads/studs if the nuts dont wan to come off because if you break a sud of in the heads you pretty much have to get new heads or take the heads off the car to repair them

[levis76]

Yeah, I did the HG a couple weeks ago and had to reuse the old studs. One stud on each side stayed in the block and the others came out with the nuts due to the buildup of corrosion on the threads. The header flanges are pretty rotted too. That's why I want to replace the header and its hardware at least. I would like to replace the rusting mid section of exhaust, preferably with something that isn't going to cost a lot and cause CELs. Anyone else using a catless system, whether you have a track pipe or you hollowed out your cats. I want to hear from you.

[sexystover]

did you do the headgaskets with the motor in the car? if so what did you have to remove to do them? im doing mine soon and dont feel like pulling the motor

[levis76]

did you do the headgaskets with the motor in the car? if so what did you have to remove to do them? im doing mine soon and dont feel like pulling the motor

Kind of off topic, but ok. It is possible to do them without pulling the engine, but for the heads to clear you have to lift the engine several inches which means you are more than halfway there. I actually saved myself time and headache by yanking it all the way out. The list of what comes off is too long, basically everything, which was another reason to do a full pull. I disconnected only the hoses, harnesses, and fasteners required to pull the engine. I did everything else out of the engine bay and it was much easier to work on.

[sexystover]

ok thanks, and on topic a way to use a track pipe but not get a cel is to use a spark plug antifouler and drill it so the o2 sensor fits, that way it tricks the car into thinking theres a cat because the o2 sensor isnt submerged in the exhaust stream

[Huffer]

I guess my question is how does the ECU use the signals sent by the O2 sensors? Are they compared with one another or are they both used individually to adjust the fuel/air ratio?

Front O2 takes a reading, rear O2 takes another one. If the O2 level isn't "high/low" enough then the rear O2 triggers a CEL.

[impreza_GC8]

You will get a P0420 CEL with a track pipe. You can space the 02 sensor out with a 02 sensor spacer or the spark plug defouler mod. Or you can wire in a resistor to send the correct voltage.