Q. I want to change the exhaust on my 2009 Yamaha XJ6. I'm happy to get a full system less the cat as I'm told it will reduce weight and increase horsepower.
Some systems that I've looked at state that the system 'retains lambda sensor', others don't mention the lambda sensor at all.
Now I'm confused. What is a lambda sensor? Do I need to retain it?
King Wasp, MCN forums
A. A lambda sensor measures the oxygen content of your exhaust gases in order to control your fuel injection; about once per second it'll signal to weaken/richen up the fuel content according to engine speed/load.
As for whether you need to retain it, it depends on your engine management system: some will run OK without it, some must have the sensor, or it'll be rough as home-made scrumpy from tickover. If you remove or disconnect it, you may get error codes.
If you retain it, make sure you don't use any silicon exhaust sealant upstream of the sensor as even the vapour can kill it in short order. I’d try and retain the sensor if it's possible.