Just got the car back from MOT with a failure due to high CO. How do i get the car to run a little leaner?

I am running a 96 STi everything standard other than a full 3inch turbo back system. As far as i can see there is no adjuster to make it leaner or richer or is there.

The other thing is i have a W6 ECU with a scoobyecu chip that is claimed to run 300bhp on a full de cat and the standard TD05. If i was to take the original Z4 ecu out and replace it with the W6 do you think it would be leaner?

Got a few hours to get her back for the MOT, any help would be good.

 

o2/lambda sensor fault as top of the list.

Tony

 

Let's do the obvious question. This "3 inch turbo back system" you've got. How many catalysts are in it?

You can't "make the car run a little leaner", the mixture is set automatically by the ECU. If you don't have any cats in your exhaust system the reason for the failure is obvious and the cure equally so. If you do have a catted system, and it failed on CO rather than Lambda, then it sounds like the cat(s) aren't particularly healthy.

 

There are no cats on this system but this is not the failure. As it is a 95 import it gets tested on base settings and not as the uk car. But also, as there are no cats would this not help the engine run leaner?

I have a CO of 2.34% with unburnt fuel at 200ppm. It does say that the O2 is .76%. Not sure what these settings need to be in the country, or at this altitude.

Also i am not running a lambda sensor after the turbo just one on the uppipe ( make that the header, sorry) , was like this when i got it from Japland.

 

The O2 semsor on the MY93-96 cars is a little further down in the driver side header elbow section, not in the up-pipe. Also, these MYs didn't have a lambda in the downpipe - that's an EGT sensor (now redundant and not fitted because of your decat).

 

Yeah! Thats the one, cheers Joz. The sensor after the turbo is not there and has a bung where it was.

So do we reckon i need to be replacing the O2 sensor?

 

yes o2 sensor

 

Cheers Simon, i followed the replies above and tried to get one online, about £150 so not the end of the world. Cheers to all.