Wrong O2 sensor position in almost all headers!

[JIM THEO]

It has been mentioned here and there and it's obvious, most of the aftermarket headers have the front O2 bung in one cylinder exit which imho is inaccurate and may lead to leaner/reacher mixtures in other cylinders!



That's why I am thinking of using the second hole (Gruppe-S UEL headers) that is for the rear O2 sensor, close to where all four pipes joined together, until I realized that even the second hole is at the exit of the same one cylinder and doesn't read from the other three!



So what do you think, if I buy another O2 bung and weld it at the end of all pipes for the front O2 sensor?
It should be on the upper part of four pipes, I'll heat wrap well the headers to keep the exhaust temps high (I think narrow band O2 read above 470C degrees) but as the metal has been shifted to that point the front O2 sensor will not be vertical to the exhaust gases route, is this a problem for accurate readings?

[CSG Mike]

If only the ECU did individual cylinder trims

[JIM THEO]

Originally Posted by CSG Mike

If only the ECU did individual cylinder trims

You misunderstood, I mean by measuring all four cylinders ECU has an idea when mixtures are lean even if this is the result of only one cylinder and adjust fueling, with most headers if one cylinder runs lean and another, say the one with the O2 bung, reach what it will do?

[Prodigalson]

What he means is that given that the fuel trims are not applied individually per cylinder, rather they are applied equally to all cylinders, O2 readings from any of the four exhaust streams will suffice for closed loop control.

[steve99]

I think what mike was getting at is that ecu only reads from a single 02 sensor


So if that sensor is reading a combination of all four cylinders like in stock position then its going to read the average afr of all cylinders so you would not rearly know if one cyliner was rich or one lean.


If you put it in one runner then you only get an accurate reading on one cylinder but dont know what ghe otjers are doing.


The best option would be four 02 sensors one per cylinder.


Also the standard ecu setup only uses 02 sensor as fueling refernece when cruising and light throttle.


In full throttle or hard acceleration fueling is based of maf sensor and fueling tables the 02 sensor is no longer in feedback loop.


In either case of one runner or combined location if you get a single cylinder injector go bad its not going to save you. The fuel trims will take ages to set a cel code even if it was the single runner monitored, even then it doent shut down engine

[JIM THEO]

If this is how our ECU behaves and can't adjust fueling if reads leaner (average) mixture then, as you say Steve, it's worthless!
Only if it has EGT sensor could save the engine as gas temperatures spike instantly from lean mixture even from one cylinder, at least this is how WRX/STI behave.

[Lantanafrs2]

I wouldn't call it worthless. Imo a serious air leak on intake side would affect all cylinders. Imo a fueling issue on 1 cylinder would cause knock or misfire eventually which would be detected.

[Lantanafrs2]

After 5 years of use I'd say the round wheel works ok.

[CSG Mike]

Well, the stock setup can also detect bank mismatches

[JIM THEO]

But with aftermarket headers (different position of secondary O2 sensor) and remap doesn't apply this, right?

[mav1178]

Decades and decades of R&D by automotive engineers and this fatal flaw has been uncovered.

[JIM THEO]

Originally Posted by mav1178

Decades and decades of R&D by automotive engineers and this fatal flaw has been uncovered.

There is no reason for irony, this has nothing to do with automotive engineers, just look where factory front O2 is positioned and what purpose serves and compare it with aftermarket headers position, yes those with the big R&D teams you mention...

[Leonardo]

Using the word "irony" instead of "sarcasm", is ironic.

[mav1178]

Originally Posted by JIM THEO

There is no reason for irony, this has nothing to do with automotive engineers, just look where factory front O2 is positioned and what purpose serves and compare it with aftermarket headers position, yes those with the big R&D teams you mention...

Then get the right aftermarket header or run a tune with a proper wideband O2 sensor. You can modify your header all you want but moving the O2 to the "proper" position doesn't necessarily mean you will get the best out of your engine performance, just a lot of extra wiring.