Lambda sensors, Have I got this right?

[Toecutter]

Am I understanding this correctly? If I have a pipe with a CAT, it requires a Lambda sensor upstream of the CAT... however, if the CAT is removed, the Lambda sensor becomes pointless?

[Bulldog9]

I've never seen a motorcycle with a Lambda sensor after the catalytic converter. Some cars have them before and after, but I've never seen a motorcycle with one after. Therfore removing the catalytic converter will likely have no impact on the Lambda cycle.

[guzzisteve]

The O2 sensors have nothing to do w/cat. The cat is to make the exhaust cleaner, that's all. You don't even need the O2 sensors unless your bike gets inspected. You can shut them off if you wish w/a click of a box in the map.

[Kev m]

Pointless? No. But how beneficial is arguable and probably varies with the vehicle (and type of sensor, narrow band or wide band).

In theory the sensors are used to dial in fuel trim. In stock form that usually means trying to maintain The best ratio for cat-con operation. In theory this should be efficient and reduce pollutants more than would be safely possible with only open loop fuel mapping.

If you like the way it runs and are happy with the mapping you certainly could continue to run closed-loop EFI even if the cats have been eliminated.

But yes, once eliminated you could also choose to run open-loop mapping only and eliminate the lambda sensor(s).

[Spokane2303]

Can you remove the Lambda sensor without destroying the catalysts in stock exhaust?

[molly]

Am I understanding this correctly? If I have a pipe with a CAT, it requires a Lambda sensor upstream of the CAT... however, if the CAT is removed, the Lambda sensor becomes pointless?

You have the lambda as near to the engine exhaust port as possible to get a accurate air/fuel ratio (AFR) reading. Some tuners state within 7" of the port but most fitted by the manufacturers don't get anywhere near that. Putting it past the cat (downstream) would not give a correct reading, so removing the cat won't effect the lambda and  conversely if the bike is properly tuned removing the lambda won't effect the cat.

The lambda is a sensor that provides data for the ecu (bikes brain) to calculate the amount of fuel required for efficient combustion. The cat is basically  just a filter to improve emissions and has no  contact with the ecu.
Performance wise there is little to be gained by removing the cat unlike the lambda that can sometimes effect the smooth running of the engine.

[Kev m]

Ok, to be clear, lambdas are used to allow the ECU to self-tune slightly to ensure proper cat operation so they are related just not directly. They can also be used for mapping (auto-tune). At the end of the day they simply tell the ECU data about the leftover oxygen content in the exhaust and therefore provide "feedback" about the air/fuel mixture and the constantly changing state of combustion in the cylinders.

Though you may be able to keep a cat on a open loop map bike you are more likely to burn it out eventually. That's why they started using lambdas in the first place.

Downstream sensors are part of OBDII protocol and are used by ECUs to compare signals with the upstream sensor and determine the effectiveness of the cat. I've never seen one in a bike yet.

[Toecutter]

Ok, that's what I figured. The Lambda sensors exist to ensure that the bike is burning fuel at the proper ratio so the cat-con can do it's job most efficiently. Perfect.

I'm a hippie... this shit matters to me. I'm toying with the notion of new pipes, and I like the fact that Zard has a cat-con.

[Kev m]

Ok, that's what I figured. The Lambda sensors exist to ensure that the bike is burning fuel at the proper ratio so the cat-con can do it's job most efficiently. Perfect.

I'm a hippie... this shit matters to me. I'm toying with the notion of new pipes, and I like the fact that Zard has a cat-con.

I totally hear ya. I run all my emissions equipment on the whole fleet.