Hi All,
My Ls400 Just failed it's national car test on a high Lambda reading. 1.13 this indicates that it's running lean. My first thought would be O2 sensors. Should there be anything else I should look for?

 

I'd rather think it's not the O2 sensor issue because of the value. I'd check the air leak around the intake portion first. It would be quicker to use a smoke machine.

 

If I were you I would also check for exhaust leaks, those mess with the lambda measurements on inspections and can cause too lean readings, Is the engine throwing any codes? If it is I would check for fuel system leaks.

I'm saying this because mine does throw the odd CEL running lean and when I did my valve cover gaskets I noticed a bit of a fuel smell close to the injectors (probably a bad seal?), honestly for now i'm not doing anything until the smell gets noticeable under the hood or the car does not run well, for now I think it's good since it is quite a big job.

Either way, first thing I would check is the exhaust and the dreaded EGR pipe.

 

Also, always follow Yamae's instructions first, he is the master of LS400 knowledge.

 

I managed to get it to pass. There was a lot of corrosion and holes on the twin pipe from the cats to the resonator. They were all covered by the heatshields which I suspect caused the corrosion in the first place.

I did a bit of a bodge job with gungum tape and putty which got me through my emessions test with a lambda reading of 1.01.

 

glad it's fixed but wow that's an interesting repair!