O2 sensors w and w/o headers?

Application: 97 coupe.

First let me state that the problem regarding this issue has been corrected. I'm just trying to understand the logic behind it.

I had a set of headers installed last week. After the install I had severe idle problems "tractoring" for about 1-3 minutes before the car corrected itself. The scanner indicated faulty Primary O2 sensors. I found out from people who had similar problems that the O2 sensors are crossed to the opposite side pipes from the factory. They found that uncrossing the O2 sensors eliminated the problem.

Why does this work?

[robertearl]

The front O2 sensors are not crossed. Only the rears. I do not believe that even if the rear ones were crossed that it would cause your problem. My guess is they fixed something else accidentally.

Reb

Originally Posted by robertearl

The front O2 sensors are not crossed. Only the rears. I do not believe that even if the rear ones were crossed that it would cause your problem. My guess is they fixed something else accidentally.

Reb

Typo: I meant to ask: Why are the rear O2 sensors crossed?

[leadfoot]

It is a frequent mistake when headers are installed that the rear sensors are replaced uncrossed resulting in codes.

[froggy47]

In a car with NO ENGINE PROBLEMS would not the o2 sensors be reading pretty darn near the same gas mixture on both sides?

Logically.


How do the sensors (or the computer) know that they are crossed (or not) on an engine that is running well?

:)

Originally Posted by froggy47

In a car with NO ENGINE PROBLEMS would not the o2 sensors be reading pretty darn near the same gas mixture on both sides?

Logically.


How do the sensors (or the computer) know that they are crossed (or not) on an engine that is running well?

:)

I have no idea why the engine freaked, but if the fronts are crossed, the computer gets cranky.

[froggy47]

Originally Posted by radioflyer97

I have no idea why the engine freaked, but if the fronts are crossed, the computer gets cranky.

:)

Not doubting, just trying to understand the mechanics of it. Maybe a tech will know.

:)

[robertearl]

The computer is constantly adding or removing fuel to maintain the currently commanded AFR. If it is trying to add fuel to the right bank and the next reading from the O2 sensors say that it got leaner it will try to add a little more fuel next time but the computer is reading what is happening on the left side. This happens enough, the PCM gets pissed off and throughs a code.

Reb

Originally Posted by robertearl

the PCM gets pissed off and throughs a code.

Reb

lol...

Okay, so why are the rear O2 sensors crossed from the factory?

[ToolGuy]

I think the point to remember here is there are 4 O2 sensors total.

Say the uppers were connected correctly.

Now say the rears were not. You would have an upper reading normal but that pipes rear getting info from the ECM that would normally have gone to the other bank or side. The first gets confused and throws a code.

FWIW... The rear sensors are the same part number, I know since I replaced mine thinking they were jingling but discovered it really was my H pipe.

I dunno, this is just what I think...


I also do not think the factory would have crossed the sensors originally, these people may be mistaken. The header installers crossed them and then re-crossed.