few questions regarding exhaust work

[trhlz1222]

1. is there o2 sensors before the cat and after or just before or just after or are they with the headers. my uncle wants to know where they all are before we do my exhaust.

2. i think i know the answer to this but i can install headers without pulling the engine right? if i can whats the best way jacks or ramps?

thanks for the help guys.

 

[posthuman63t]

4 - o2 sensors.

2 in the front header, 1 in the rear header, and one in the y-pipe. All before the cat.

 

[posthuman63t]

and yes, you can install the headers without pulling the engine. It's a little bit of a pain but it can be done and has time and time again.

 

[getsum111]

Check out Tourige's how to in the old forums. Good write up, lotsa pics.

 

[Tourige]

Check out Tourige's how to in the old forums. Good write up, lotsa pics.

This man speaks the truth.

 

[getsum111]

This man speaks the truth.

I think you're a little biased. :laugh:

 

[Tourige]

I think you're a little biased. :laugh:

It was a damn good writeup i must say

 

[trhlz1222]

thanks guys

 

[Big Jim]

A little clarification is in order. Your car has three cats. Two of them are precats built into the exhaust manifolds. You will lose them if you install headers. Two of the O2 sensors are in front of the precats. These are the two that your PCM need to regulate the injectors. The next two are behind the precats but in front of the main cat. These are cat monitors, helping the PCM to tell if the cats are working efficiently. With the precats gone due to header installation, you will turn on the check engine light (MIL) and set cat inefficiency codes. To prevent that, you will need to add MIL eliminators. MIL eliminators require working cat monitor oxygen sensors.

 

[getsum111]

It was a damn good writeup i must say

Yes it was, that's why I used it. :laugh:

 

[KyleQ]

A little clarification is in order. Your car has three cats. Two of them are precats built into the exhaust manifolds. You will lose them if you install headers. Two of the O2 sensors are in front of the precats. These are the two that your PCM need to regulate the injectors. The next two are behind the precats but in front of the main cat. These are cat monitors, helping the PCM to tell if the cats are working efficiently. With the precats gone due to header installation, you will turn on the check engine light (MIL) and set cat inefficiency codes. To prevent that, you will need to add MIL eliminators. MIL eliminators require working cat monitor oxygen sensors.

Regarding MIL's - do you need to install one or two? I mean, in just the y-pipe or in both the post manifold locations?

 

[getsum111]

Need 2 MIL eliminators, one to replace each of the lower O2 sensors, ie, the two in the y-pipe get replaced.

 

[Big Jim]

MIL eliminators do not replace the downstream oxygen sensors. They modify the signal from the oxygen sensor. MIL eliminators are added to the circuitry of the downstream oxygen sensors.

 

[getsum111]

Doh!!! :blackeye: That's what I meant, that they splice into the downstreams. And I even have these on my car now, LOL. Thanks for the clarification, Big Jim.

 

[trhlz1222]

so even tho the headers have all the hookups for the existing o2 sensors i still need to get mil eliminators?

 

[Big Jim]

Once again, yes. With the missing precats, (missing because the precats were in the stock exhaust and not in the headers) you will set codes and turn on the check engine light (malfunction indicator light or MIL) and set codes for inefficient cats. The engine will run fine, but the light will be on.

 

[trhlz1222]

so whats the point of even putting the stock o2 sensors in the aftermarket headers if your just fooling the engine with MILs?

 

[Big Jim]

Your not fooling the engine. You are fooling the computer so it doesn't turn on the check engine light, set codes, and possibly interfere with a smog test.

 

[trhlz1222]

where can i get MILs from then?

 

[Trikeman72]

asking a stupid question

asking a stupid question

4 - o2 sensors.

2 in the front header, 1 in the rear header, and one in the y-pipe. All before the cat.

I am failing to locate my 4 o2 sensors.. i have a 99 contour with a 4cyl.. i see a sensor on the exhaust manifold above the cat thats right there bolted to the exh man. i see another one just below the cat thats bolted to the exh man. and for the life of me i cannot find the other 2 or the other "bank" that everyone is talking about????? the goofus at autozone forgot to notice the code number.. but said something about the o2 sensor left bank?? and something about the heat something malfunctioning??? now the CEL is off cuz he reset it so i dont know what flippin sensor to change???? or how to find the other 2.. the car was missing like mad no power etc and the cat bolted to the exh man was cherry red so i figured it was plugged.. cut a hole out of the botom of it dug out the honeycomb welded the hole shut.. same prob.. some ppl are talking about a pre cat and a cat.. is the cat thats bolted to the exh man the only cat on this car or is there another one on back the line somewhere? i dont see nothing after the exh man one but a silver looking mesh like pipe then the pipe goes on to the back of car???
someone help
bill