O/T Dead BMW Lambda Sensor & Cats - Any side effects?

[New Cat]

My tintop failed its MOT on emissions and was diagnosed (by a friend) as having a dead lambda sensor which had clearly been dead long enough to be pumping lots of hydrocarbons into the now dead cats...

 

Once all this is sorted am I likely to notice any improvement in fuel consumption ? or anything beside fewer gassed little animals and plants on the side of the road 😬

[Bare]

Interesting question..

dead O2 sensor will likely dump less Fuel into the cat than a new one

It's purpose is to ensure there is enough unburned fuel and oxygen available for the Catalytic to Catalysise (burn, for us unwashed :-) the exhaust clean of the legally sanctioned substances.

Cats are Tough! Even several consequetive tanksfull of Leaded can be run thru the things with small long term effects. Clogging is THE killer (along with Silicone but that's not a normal occurence)

Suggest trying to look thru the thing before paying a large sum for a replacement. should see light thru it.. it looks like a miniature Honeycomb.. the degree of clogging is a good indicator of life left.

O2 sensors ARE universal ..only differences in almost all variants is the # of wires for their built in preheaters and the connectors specific to each car's harness.. often the skill/ability to splice the wire connectors can save significant coin.

G' Luck

[Bob Corb]

Lambda sensors cost on a few quid, change them first then re-test. You can kill a cat due to excessive overfueling/lean running and over heating but the ECU in a beemer will have a failsafe mode which should protect them. Sometimes an apparently dead cat can be resurected by going for a long cruise down the motorway not too fast (<80mph). This will get the exhaust hot but still running closed loop and will allow the cat to burn off any muck etc.

 

BC

[New Cat]

Thanks for the tips guys. The car is being sorted by an old friend of mine whom I trust so I'm not too suspicious...

He replaced the lambda sensor first and did a re-diagnosis, finding the 11yr old 150,000 mile cats to be dead.

He said he could probably get an 'MOT' from somewhere without replacing the cats but that the problem, would not go away on what is otherwise a good sound car - so I'd have to find a friendly MOT station every year. I think it better to replace the cats!

 

He is ferrying the car backwards and forwards for the tests, has replaced the lambda sensor and will now replace the cats for around £500 (obviously not OEM BMW cats...) all in. Seems reasonable to me.