02 sensor issue

[dsm4444]

Would your engine light turn on if your o2 sensor was going bad? I think my sensor behind the cat is going out. My fuel milage is horrible and i keep getting a surging issue. The surge goes away for a day or two everytime i rewire my sensor. Now i know for sure the sensors soldered on there well and its still acting up. But no check engine light....?

 

[Locke]

The CEL will light when either o2 has an out of range signal, or a heater circuit malfunction. There is also a CEL if the reading from the downstream o2 is the same as the upstream's.

The downstream sensor has no effect on your engine.

 

[dsm4444]

Well i know thats not true because when i first rewired it i left one unwired on accident and it sent my engine through hell and back til i found out.

 

[turbosax2]

This thread is somewhat relevant.
http://www.dsmtuners.com/forums/showthread.php?p=151161457#post151161457

 

[oldman]

Well i know thats not true because when i first rewired it i left one unwired on accident and it sent my engine through hell and back til i found out.

It is true, the only function of the rear O2 is to tell the ECU that you have a functioning CAT and will have absolutely no effect on engine operations.

 

[dsm4444]

Ok i believe you but would it have an thing to do with the fact that its a straight through cat? Maybe thats sending something wrong?

 

[oldman]

Ok i believe you but would it have an thing to do with the fact that its a straight through cat? Maybe thats sending something wrong?

No, the reason the ECU wants to know if you have a functional CAT is for emissions purposes, you can run an open down pipe and your engine wouldn't care. The front O2 however will directly affect your close loop operations.

 

[dsm4444]

o i c.. So ill check out the sensor on the down pipe. How often do those sensors go out? i have a 95 talon.

 

[oldman]

o i c.. So ill check out the sensor on the down pipe. How often do those sensors go out? i have a 95 talon.

It is very hard to say, many things can facilitate the process, running pig rich for example.

 

[dsm4444]

k Well i took out the front o2 sensor and found that its chalk white... is this bad.. the one in the rear is blackened. I understand that the front one takes the most heat being right on the headers but still...