Exhaust O2 sensor position

[wagonist]

Has anyone got any input into how important this is?

I've got a 4 wire sensor and I've swapped over the factory 4-1 manifold which included the cat converter close to the engine to a manifold off an older model that had 4-2-1 and then a cat under the firewall.
I did this to ditch the cat altogether (because its a track car).

The original manifold had the O2 sensor just before the cat, and therefore in front of the engine.
The now fitted manifold also had the O2 sensor just before the cat, but this means down near the firewall.

I may be able to redo the wires, but there is a chance of going turbo later, which would mean the sensor going back to close to the engine.

Is it much issue to fit the sensor into only one of the pipes in the 4-2 section? As this is only sensing from 2 cylinders, not 4.

I'd love to just plug in a loom extension, but finding the right car at the wreckers to get the plugs has proven to be difficult.

[oldcorollas]

not realyl an issue, unless you have a problem on the other 2 cylinders.
and... O2 sensor only really used to improve fuel economy in part throttle operation
buy new plugs.

[thechuckster]

Personaly, i would extend the wires, they're not the special type you get with thermocouples, plus having sensor to close to a turbo will overheat it. I wouldn't do the same to a wideband sensor as it is calibrated as one unit (sensor+tail).

[wagonist]

I may be in luck.
I unwrapped the tape off the loom and I may be able to separate out the O2 sensor wires far enough so that the plug can reach to either side of the engine.
Will have to refit the loom to the engine to check this.

[oldcorollas]

what, why would you put the sensor closer to the engine with turbo? makes no sense... better to be further away

[wagonist]

No I can possibly move it to the back of the engine to suit the 4-2-1 manifold (after the 2-1 collector), and even leave it on the back of the engine if I go turbo (which would be on the front).

[George]

oldcorollas, in fact the O2 sensor is used for the best power,too. Open loop mode (WOT) still uses long term fuel trim obtained in closed loop operation (partial load).

[Duk]

Personaly, i would extend the wires, they're not the special type you get with thermocouples, plus having sensor to close to a turbo will overheat it. I wouldn't do the same to a wideband sensor as it is calibrated as one unit (sensor+tail).

Quite often the signal is sent down a shielded cable, so something to consider if/when extending wiring.

what, why would you put the sensor closer to the engine with turbo? makes no sense... better to be further away

While a little off topic and not really relative to factory cars use of EGO sensors, if you put a wide band AFR meter in a car, the further the sensor is from the exhaust ports, the greater the time gap between what has happened and what the AFR meter shows, especially at low loads where the gas speeds and volume is much lower.
For my own cars, I like to install the wide band sensor as close as I safely can to the engine.

[oldcorollas]

that is a problem for un-heated sensors, but with heated sensors it is much less of an issue.

george, some ECU's may but not all, and very unlikely with aftermarket setup.
the engine in question is a Hyundai motor? not toyota.

[wagonist]

yeah, Hyundai, but generally would be the same.
The plug into the loom is only about 100mm away from the sensor, and the shielding only goes for 30mm before the 4 wires are exposed.

I remember my old Subaru Leone Turbo which had a single wire O2 sensor was shielded all the way back to the ECU!

[George]

I'm 99% sure that all newer (say post 1995) engines would use similar correction strategy. Ecology standarts demand low emissions in all modes over extended periods without any servicing. The only option to comply them is to extend fuel correction to WOT and even cold start modes.

[oldcorollas]

not sure how old the motor is in his race car..

Steve are you still using (and going to in future) the stock ECU?

[thechuckster]

the sensor will only be a narrowband unit, so the any AFR correction will be at warm idle and cruise only. Under power these things will revert to factory map - and being a rally car, it'll be mostly WoT making the sensor data somewhat pointless.

They're not Euro-IV compliant motors so correction strategies in the ECU are going to be limited.

In any case, Steve will have to run aftermarket ECU when turbo-ing the excel motor.

[George]

thechuckster - nah! Under WOT there will be factory map PLUS some pre-calculated correction, based on data collected when in cruise modes

[oldcorollas]

george, when (year/model?) did each manufaturer change to that enrichment scheme?
not all ECU's do that.