Help, people with mk2 172’s and decat

[Big Iain]

Ok I have purchased a Janspeed decat form my mk2 172 which has two lambda sensors, 1 before the cat and 1 after.

When thinking about this the two sensors are obviously giving the ecu different readings with the cat on but with the decat fitted the two readings should then be the same .

So what I want to know is will this affect the ecu ie giving it b****cks info from the second sensor and not running as well??

The cat is there to bring down emissions right?? so if the second sensor is getting the same reading as the first would before the cat will it not then think there is too much fuel going through and in turn reduce that??

Im lost!!

Do I have to get a chip or ecu at the same time as a decat??

 

[McBunny]

right i was lucky enough to only have to worry about 1 lambda sensor on my phase 2 172

if your worried just unplug the second sensor and just put a blanking plug in the hole.

you might need a chip it depends on car tho as each is different

 

[Big Iain]

I hear what u are sayin bout the blanking plug but the sensor will still be active. I am quite worried bout this as the lamda sensor failed on his corsa and it ran like a bundle of sh*t

 

[McBunny]

no you unplug the sensor, you gotta remember i had it runing on one lambda for 6 months with decat and now i have a cat on and only 1 lambda pluged in.

you dont just not screw it in you dont have it connected to the car you disconect it

 

[Big Iain]

oh right, why did you take it off??

 

[McBunny]

why did i take teh second sensor off ??? as my decat was for a mk1 and there was only one mounting point and when i refitted the exhaust the lambda sensor was about 150 miles away lol i have it back now and need to refit it but cant be arsed

all the second one is there to do is control emmisions at startup. basically when its not there it thinks its warm and chucks more fuel in aparantly acording to the mechanic it does not produce an error code as the system was designed to only have 1 lambda ala phase 1 172 so dont worry the second aint needed

 

[Rick_172]

This has been done to death Iain. The second sensor is there basically as a tester sensor for the main sensor. Its just there to make sure the first one is working properly, and the ECU doesnt make any comparisons between the readings of the two to make the mixture.

Do another search bud, cos others have explained it better than me!

 

[Big Iain]

any reno techs help me out with this??

Is it an easy job???

Dogmaul did you notice the power increase much?? so if I plug the second sensor in it should be ok??

 

[McBunny]

yes very easy to take off second sensor its just a plug in connector.

taking the cat off can be a b**ch tho really needs 2 people

yes big power increase with decat

yup with second sensor in should be fine

 

[Big Iain]

I dont get why its a tester sensor if ther is one before and after the cat??

will go have a search!!

 

[wackojacko]

Although I would get your car Rolling Roaded afterwards to make sure everything is fine.

I was told mine was running very lean. But i want a second opinon before I get a chip.

 

[McBunny]

its not a test sensor mate its there to check things at startup for cold starts part of the new emmision regs

 

[Big Iain]

so it wont do ne harm being plugged in or best to jus remove it??

And so really its nothin to do with the cat and could be put ne where after the cat??

 

[wackojacko]

I would go with unpluging it.

Ive had mine plugged in and unplugged and me car seems to be running better with it unplugged.

Its probably a mental thing though......

 

[McBunny]

iain just unplug it might aswell look at it as a weight saving too

 

[Big Iain]

arrrggghhhh!!!

What to do what to do.............

 

[Big Iain]

Reno techs please help.... do I need this plugged in or not??

Its booked in for friday morning to be fitted so the way its lookin now is leavin it unplugged!!

cheers!!

 

[McBunny]

you DONT need it plugged in !!!! works without it lol how many months do i need mine running without 2 lambdas to prove this

 

[Big Iain]

ok so take it out all togetha!! both ends!!

and it runs alot better without a cat??? noticeable??

 

[McBunny]

yes much better without cat you also then get pops n bangs and stuff

when you unscrew the lamda sensor follow the cable up and you get to a plastic conection block just unclip the sensor bud

 

[Big Iain]

jus need to find a way to block the second hole!!

 

[McBunny]

didnt it come with 2 big nuts one in each hole ???

 

[Big Iain]

aint got it yet will have a look on friday

 

[Neil82]

Mine is fitted with both sensors plugged into the Janspeed de-cat.

 

[Joethrelk]

Mine has both sensors plugged into the decat pipe and it has been running fine and noticably quicker since it was changed..

 

[jonnyboy]

mine runs with both sensors in no problems at all

 

[JAY172]

the second sensor is to allow the obd to self test the cat converter operation. Most people seem to just unplug it without any problems(this should in theory put a warning light on but it doesnt). you can use a sump plug and copper sump washer as a blanking plug as they are the same size/thread as the oxygen sensor. you will only have running problems if you disconnect the first sensor as this is used by the injection system.

 

[visceral]

Iain - how mucho was the de-cat? And where u get it from mate?

 

[Big Iain]

121 from motorsport world!!

 

[CUPPY]

you got it on yet then mate?

 

[Big Iain]

its on yeah

 

[yeecup]

notice any difference with the de cat?