when you have fitted a de-cat what happens to the lambda sensor or do you just leave it in.

reason i ask is on the bm 540 (2 cats fitted)i have 2 pre-cat and 2 after-cat lambda sensors ,surely the ones after the cats will sense something is up and flash a engine light up.

the touring i have only has 2 before the cats,so would it be just a case of de-catting?

cheers
dave

 

As you say ones after the cat are to check the effectiveness or not of the cat and will flash warning, and may even shut engine down.
Upstream are ok though for decat
tabetha

 

thanks for that

so the saloon is a no go but the touring is fine for a de-cat

dave

 

After cat(downsteam) hegos are a no no for decat!!
Upstream are ok.
tabetha

 

do the rspca know this is going on?

 

what you can do is remove the 2 second 02 sensers and just cable tie them somewhere out the way in the engine bay, although remember they may get get if heated so dont cable tie them to the wiring loom!

now the sensers will read fresh air, therefore think the cat is being mega efficient!

plug the holes in the exhaust with spare bolts, if you check ebay you may find a box to plug into the 02 senser wiring to fool the ecu, pretty sure graham goode does them for the st170.

 

I dont think its as easy as hanging them in the fresh air - its tricky to do without cats on an M3 and £750 race cats are the regular option - people wouldn't pay £750 for something if they could just hang the oxygen sensors in the air

RW