Why more than one Lambda sensor / best place to put the sensor?

[TopQ1967]

Hi,

 

Looking at a new Caterham, I noticed two Lambda sensors. Why two?

 

I have two lambda bungs on my exhaust. One in the motor bay at one of the exhaust pipes(here was the original lambda sensor) and one in the exhaust after the 4-1 joint.

 

What is the best place to put it now? (I am doing to install a wide- band LC-1 Innnovate sensor).

 

Regards

 

 

Quirin

 

[Frying Pan]

They are pre- and post-catalyst (or upstream and downstream) sensors, a requirement of EU-IV emissions to monitor catalyst performance. If the ECU sees little change between the two, it will illuminate the MIL (does Caterham fit on on the newer cars?) to warn of catalyst failure.

 

We have four on our V8s - pre- and post each bank's catalyst!

 

If you only fit one, then it is normally fitted pre-catalyst as per the K-Series Sevens.

 

-----See some pictures of the build here. 12000 miles completed!

 

Edited by - 7heavensoon on 10 Aug 2007 08:04:51

[TopQ1967]

Thank you 7heavensoon,

 

I don't run a cat (R400 engine).

 

But what is better fitment in one of the 4 exhaust pipes in the engine bay, or after the 4-1 joint?

 

Q.

 

 

[rj]

Provided your exhaust is 100% leak free and the TBs are perfectly balanced it doesn't matter

 

 

/r

[Frying Pan]

Not sure it matters greatly - possibly the port after the 4:1 joint will be better, just in case the relative cyclinder efficiencies vary.

 

I guess (I'm no expert ) it comes down to which is easier to get to...

 

Guy

 

---

See some pictures of the build here. 12000 miles completed!

[C7XAY]

I was advised by Northampton Motorsport the best place was after the 4-1 joint. As Guy says cylinder officienes may vary.

 

Ray

[rj]

This would be true if you had a cat on the car - to make it work properly.

 

You have no benefit from averageing the cylinders if you have no cat as none of them will then run perfectly.

 

/r

[Peter Carmichael]

Just a couple of points...

 

1. TB balance will affect getting the emissions clean at idle (I am suggesting using emissions to tell you whether your TBs are in balance) and have less effect as the throttle is opened

2. If putting a sensor after the 4-1, your exhaust needs to be 100% leak free without using silicone sealant. Silicone poisons lambda sensors.

[oilyhands]

And one more point, having the sensor at a confluence point will be a better position for mapping, even if you are not using closed loop during normal running.

 

Oily

[ECR]

Specialised lambda friendly high temperature exhaust silicones are available....

[rj]

Specialised lambda friendly high temperature exhaust silicones are available

 

Where from please - quite urgent in fact as I have an RR session comming up very soon...

 

 

Oily,

 

 

I'm not sure I agree with you here as you may be at risk by having the average value rather than the leanest - which probably isn't cylinder four, where the boss is on most Caterham exhausts, if you have an airbox fitted, but... I'll hopefully be monitoring the primaries with an infrared camera (a 4k£ Fluke kit) during the RR session to se what happens and act acordingly.

 

 

/regin