Header install- Confused about re-wiring o2

[gotta240]

96 240sx, stock ka24de, 0bd2
Just got the hotshot header...this thing is SEXY!!! LOL.

I'm confused about WHY they say to extend the second o2 sensor. It says to move it behind the second cat to get "proper readings".

Heres the confusion

s14's only have ONE true cat, which is totally replaced with a header. Should i just put the second o2 sensor before the collector gasket(where it is already threaded for one) or should i move it further back on the exhaust...if so, WHY!?!?!

thanks

[98koukile]

Well the second O2 is behind a cat, so I'm guessing they're trying to put it behind at least one cat... even if it's not the true one

[projectRDM]

The secondary oxygen sensor is used solely for monitoring the operation of the catalytic converter. By placing it in it's original location you'll trip the CEL because the readings from both units will be the same, making the ECU read that the cat is not functioning.
To prevent that, Hotshot suggests using a Catco/Random Tech/etc replacement catalytic converter after the header and fitting the rear oxygen sensor into a bung on the back side of it. In this case, the harness will not reach.

If you don't mind the CEL, screw it right in, or plug it and leave the plug hanging.

[gotta240]

thanks for clearing that up. I wish hotshot clarified that i should buy a cat!! lol. It just didn't make sence moving the sensor back 2 feet, but with a cat inbetween it makes perfect sence.

My question now- Doesn't a CEL mean you are in "safety mode" meaning the car runs rich and not at optimum?

[projectRDM]

No.

CEL is for emissions control issues only. The car could care less if there's a hundred missing sensors as long as it has the required ones plugged in.

[gotta240]

Doesn't it run in limp mode if a Fuel or Air sensor(or even knock) is bad that could cause a lean situation? OR am i COMPLETELY wrong and confused?

[orion::S14]

^^^ Completely wrong and confused.

There is no "limp mode" to speak of built into a 5-speed ECU.

(For clarity...there is a trans limp mode, stuck in 2nd gear...but not a "reduced power" mode).

- Brian

[gotta240]

so then if a primary 02 sensor goes bad, CAS, or knock sensor goes bad, driving it could actually harm the motor as it doesn't "protect itself"???

[The Chad]

hey man i ran into the same problem. You can also get an extention bung and thread it into the secondary O2 sensor hole ...this places the O2 sensor further out of the exhaust's path so it reads less flow. THis idea is common in many cars...has worked for me so far.

[orion::S14]

so then if a primary 02 sensor goes bad, CAS, or knock sensor goes bad, driving it could actually harm the motor as it doesn't "protect itself"???

Normally, no.

If you have a bad primary O2, or CAS...the car will run very poorly.

if the knock sensor goes bad, it will pull timing all the time...so it will drive like sh!t, and maybe not reach redline (without bucking).

SO...there's protection built in...and it's a hard motor to hurt!

- Brian