Where to Place O2 Sensor Bung on a V8

Robrover · Post by **Robrover** » Fri Dec 14, 2012 3:08 am

I’m installing an AEM UEGO wideband on the 4.6 SD1 and am unsure whereabouts to place the O2 sensor bung.

I understand about 18 inches from the manifold face is ideal, but this means it will either have to be in left (passenger side) bank manifold downpipe or right bank manifold downpipe.

On the US forums they tend to go for their drivers side bank i.e. our passenger side, which it is claimed tends to run leaner (not sure why that is).

Putting the sensor in one manifold downpipe would only allow it to read that side of the engine. Would this be a problem?

Or can I put it at the end of the exhaust Y section under the car so it senses the exhaust from both banks of the V8. Is this too far away from the engine?

sidecar · Post by **sidecar** » Fri Dec 14, 2012 6:11 am

My LC1 probe is in one header maybe 18" from the head, it does work OK but the reading can flicker a bit. If I had the choice I'd have fitted the probe where it can read more of the cylinders. Other engines that I worked on with this setup do have a more stable reading.

I don't think your Y section would be too far away but if it uses slip joints make sure that they don't leak air. (I suspect that it will be all welded so it will be fine)

r2d2hp · Post by **r2d2hp** » Fri Dec 14, 2012 8:07 am

I fitted mine in the collector eg where the 4 pipes come together on passanger side. Seems to work ok.

DaveEFI · Post by **DaveEFI** » Fri Dec 14, 2012 9:25 am

I have a Rimmer Bros sports exhaust on my SD1 - bigger diameter than standard - and mine is fitted after the two branches join, so rather further back than recommended. But I've never ever seen the heater come on after starting. MegaSquirt has a transport delay algorithm for coping with different distances.

ChrisJC · Post by **ChrisJC** » Fri Dec 14, 2012 4:48 pm

You have to remember that each engine bank has two cylinders fuelled from each carb. So the oxygen sensor will be seeing the average of the two provided it's being fed with the gas from four cylinders. Therefore I stuck mine right by the 4-into-1 join on one car, and the other car had the sensor just after the 4-2-1 join.

Chris.

DEVONMAN · Post by **DEVONMAN** » Fri Dec 14, 2012 10:35 pm

I welded in a threaded boss on both sides of the engine and initial side to side comparisons were possible. Unless I now get some hint of a problem, the sensor stays on the nearside as access is better due to the steering/starter etc on the offside.

Regards Denis

Robrover · Post by **Robrover** » Sat Dec 15, 2012 12:41 am

Yes that's what I was thinking too - maybe mount a sensor bung in each manifold on either side and swap the O2 sensor over from time to time to get the readings.

The problem with mounting it too far down the pipe under the car is that it may be too cool for the sensor to work properly. And there's also the risk of a tiny air leak where the two manifolds bolt up to the Y section, which would influence the readings.

I found this PDF about Tech Edge installs which suggests
"Sometimes the requirement for the sensor to see both banks of a split exhaust system dictate that the sensor is located up to 1.5 m (60 inches) or more from the exhaust valve. This may be a too-cool borderline position ..."

http://www.wbo2.com/lsu/lsuinstal.pdf

DaveEFI · Post by **DaveEFI** » Sat Dec 15, 2012 9:25 am

If it gets too cool, the heater will come on. This has never happened (apart from at switch on) with my Tech Edge.

sidecar · Post by **sidecar** » Sat Dec 15, 2012 9:44 am

I thought that Innovate even had some sort of device that allowed the probe just to be fitted right at the end of the tailpipe which is not very hot at all. I have also heard that the back of the probe must be in clean air, something to do with an 'oxygen pump'.

I can't see the readings being very good at the tailpipe though!

Quagmire · Post by **Quagmire** » Sat Dec 15, 2012 10:30 am

My lc1 is fitted just rearward of the y-piece where both banks meet (this is on a lr90). No problems...

stevieturbo · Post by **stevieturbo** » Sun Dec 16, 2012 7:11 pm

Just fit it wherever is handy, but not too close to the exit where it may see fresh air under some circumstances.

And the heater is powered at all times.

DaveEFI · Post by **DaveEFI** » Sat Dec 22, 2012 9:40 am

stevieturbo wrote:Just fit it wherever is handy, but not too close to the exit where it may see fresh air under some circumstances.

And the heater is powered at all times.

On my Tech Edge WB, the display says 'heating' at switch on, before changing to the AFR readout. So I assumed the heater is only used until the exhaust gasses keep it up to working temperature?

IIRC, narrow band types may well run the heater at all times.

stevieturbo · Post by **stevieturbo** » Sat Dec 22, 2012 2:53 pm

DaveEFI wrote:
stevieturbo wrote:Just fit it wherever is handy, but not too close to the exit where it may see fresh air under some circumstances.

And the heater is powered at all times.
On my Tech Edge WB, the display says 'heating' at switch on, before changing to the AFR readout. So I assumed the heater is only used until the exhaust gasses keep it up to working temperature?

IIRC, narrow band types may well run the heater at all times.

Most WB's will do that as the sensor is starting from cold. But the heater remains active at all times on all lambda sensors fitted with a heater.

Most importantly a wideband though, as temperature control inside the sensor is critical to getting accurate readings, which is also why it isnt recommended to site the sensor too close to the turbocharger, as temperatures there firstly can skew readings as they will be higher than the sensor can cope with, plus the heat also risks damage.

But when mounted at a cooler location, the sensor/heater has full control over sensor temperature.