Giulietta QV downpipe question - Alfa Romeo Forum
You are currently unregistered, register for more features.    
Tuning & Upgrades Discuss performance enhancements for your Alfa Romeo

Thread Tools
(Post Link) post #1 of 3 Old 17-09-17 Thread Starter
Status: -
AO Member
Join Date: May 2014
Location: Denmark
County: Egedal
Posts: 542

Member car:

Giulietta QV

Giulietta QV downpipe question

I've been thinking of replacing the very restrictive looking cat and downpipe on my Giulietta QV, with a custom build one with a 200 cell cat.
There is a lambda probe (or o2 sensor?) in the downpipe, right in front of the stock cat. On the new cat I'm thinking of buying, there is a hole for that as well.
But, there is also a second lambda probe, after the cat, right? I've read that this can cause problems if you change to a higher flowing cat or go completly cat-less, such as only being able to run the car in N and getting the check engine light.

My question is, what is the purpose of this second probe? I've read that you can fit a lambda faker on it or simply map it out of function. Will this affect fueling in the engine? And will the car still be able to pass an MOT?

It would be nice to hear some experiences from people who know about this or have changed the downpipe on their own car :-)
Esser is offline  
Sponsored Links
Status: Race cars in progress
AO Silver Member
Gertie's Avatar
Join Date: Oct 2007
Location: South Africa
County: Gauteng
Posts: 5,992
Here in SA we don't have strict emissions laws, so many guys remove the cats completely from the down pipe (custom down pipes). The 1st lambda sensor is for fueling control and the second lambda is to check if the cat is working OK. Some put a thicker bung for the second lambda to pull it a bit away from the airflow thus making the lambdas read ever so slightly different. This has mixed results, most (including me) just fit the lambda's +/- where they were and it generally works OK.
Gertie is offline  
Status: Abarth is running strong
AO Gold Member
Master Paul's Avatar
Join Date: Aug 2009
Location: South Africa
County: Gauteng
Posts: 7,627

Member car:

Dodge Journey

General rule of thumb

any 1.4 (Tjet or MA) needs a lamda fooler
Any v6 or 1750 does not need a lamda fooler
i know the 2.2 does but it still doesnt work as well
Master Paul is offline  

Go Back   Alfa Romeo Forum > Supported Alfa Romeo Models > Technical & Vehicle Assistance > Tuning & Upgrades

downpipe , giulietta , question

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

For the best viewing experience please update your browser to Google Chrome