Hi all,

Hoping someone can help.....

My 1994 wrx failed its MOT the other day on the lambda and CO readings.
The tester said this is most likely due to a hole in the cat pipe just after the cat.
I purchased a second hand cat pipe but when I went to take my original one off, I discovered they are different....

Original cat pipe;- has no input for lambda sensor. This is because it is situated pre turbo (so I'm told). BUT, it does have an input just after the cat with, what I'm told, is a temp sensor.

Replacement cat pipe;- has input for lambda sensor just before cat but has no temp sensor input.

I was told that my original cat pipe is a rare type that would be hard to find and that I could fit the replacement cat by blanking off the lambda input and then disconnecting the temp sensor as it doesn't do anything.
This concerned me as I know these engines are fussy and obviously, I do not want to damage my engine.

If anyone has any thoughts it'd be much appreciated.

P.s. sorry about the long explanation !!

 

Could you modify your new pipe so that the temp sensor is in the same position as on your old pipe ??? Doesnt sound difficult to do and a local fabricators should be able to do it for you.

I am not familiar with the engine control unit on your car but I would imagine that the temp sensor is used for keeping the fuel mixture/turbo safe etc. so I would not recommend disconnecting it.

 

the lamba sensor is on or around your up pipe (Between engine and turbo)

The sensor after the CAT is simply a "Help my CAT is on fire" sensor. Some people (Including me) remove these when you either decat or fit a sports cat. it isnt needed realy and disconnecting it will not affect running in any way.

As for the leak possibly causing the MOT Fail readings, this leak could be anywhere between your CAT and tail pipe so have a look at all the joints.

I also have an after market CAT downpipe like you which had an extra screwed boss in the side of the pipe between turbo and cat. just blank it off and disconect that old temperature sensor. all will be fine.