Catalytic Convertors

[*Glenn* 854]

Oxygen sensors alter fuel trim and correct fueling issues, like air leaks and air mass sensor faults to look after the engines. Early cars have only pre cat, removing the cat doesnt effect there operation. Later cars have pre and after cat sensors. They work in tandem and still control fuel trim (together) Yes you will get a cat deterioration fault code if the cat is faulty, however they both control fuel trim... I've been there, done that, it doesnt work. Do what ever pleases you to do with your car. As a professional and serving the industry and customers, I advise not to remove cats from cars with pre cat & after cat oxygen sensors unless you are going to run and aftermarket control system that is tuned to regulate fuel & ignition control.

BTW a reputable exhaust specialist in Auckland did this to an Audi A6 V8.. after 2 weeks the engine was (*****) it was proven that removal of the cats did the damage.

[CamB 48]

They work in tandem and still control fuel trim (together) Yes you will get a cat deterioration fault code if the cat is faulty, however they both control fuel trim...

All I wonder is if there is some sort of documentation showing this. All evidence I find (which is generally low-trustworthiness internet evidence) suggests the opposite. (edit - I must stress, it really is ALL evidence, as I can find none that suggests the 2nd sensor has input into the a/f ratio etc).

Edited June 23, 2009 by CamB

[*Glenn* 854]

I had doubts some time ago... all manufactures that supply vehicles with pre cat & after cat sensors specify you cant remove them. We had a E46 318I M43 at work for some time that we had fitted a new air mass sensor to.. all systems and live data was correct to specs. We took the cat out.

(1) Engine check light on

(2) Fault codes:

Oxygen sensor (1) & (2) out of scale

Cat Deteriation

Fitted aftermarket cat... same fault codes

Tried high flow cat... same fault codes

Refitted original cat... no fault codes and everything within specs

Why would I bother looking for a solution to overcome an introduced fault that the manufacturers say not to do ?

Some might want to...thats fine... research...research .... research

I fix vehicles for customers that rely on my advice and pay a reasonable price for what I do

I will not expose myself to risk or put myself in a position of compromise.

If you can find a solution... fine...what will be the gains ? probably nill

Risks? small ?? huge ??

Just my 2c... and I really dont need to provide proof... I do what I feel is right for my customer & myself.. others may differ

[CamB 48]

I fix vehicles for customers that rely on my advice and pay a reasonable price for what I do

I will not expose myself to risk or put myself in a position of compromise.

I absolutely respect this - I wouldn't personally recommend people remove the cat (I agree - unlikely to do much for most, however it will/does on a turbo Skoda), but find myself in a position where its already gone... so am basically just looking for an answer for me.

Edited June 23, 2009 by CamB

[ieasti 0]

so what exactly happens for the many e46fanatic members that install headers on their car?

as far as i know, their cats reside in their headers, and as such, many of them run catless, or aftermarket cats.

Most of them do have a CEL light, some may try to use spark plug non-foulers or software to solve the CEL...

but regardless of cats or not, they were still able to dyno and increase in power...

if it was damaging the car, and the computer was in fact responding to the readings of the post-cat sensors, shouldn't they see a reduce in power rather than an increase???

hmm... this also fascinates me, for most of my time I have only been reading information about US spec cars, but not our EURO spec cars...

I was told that we have 4 cats?? 2 in the headers, and 2 in the exhaust, and it was fine to pull the two in the exhaust..

[smiddy 76]

Mate, You should have M54330 eng in your car with mid mount cats[Euro].

Short header will bolt up. Long needs welding.

[*Glenn* 854]

I absolutely respect this - I wouldn't personally recommend people remove the cat (I agree - unlikely to do much for most, however it will/does on a turbo Skoda), but find myself in a position where its already gone... so am basically just looking for an answer for me.

I've tried finding info too, everyone is just saying you can't and that they won't in the industry. It's got me curious too Cam.. if you find anything, please let me know. Thats why we spent time trying it out on the E46 (cost me $400 with Pitstop just to try what we did) to see if we could find a reason. Without a cat the E46 oxygen sensors read quite differently and fuel trim went out of scale trying to compensate causing the engine check light to stay on, I think we stored the fault codes & live data info on a PDF file.....I'll look later, even with some Chase muffler aftermarket cats fitted, which we have used alot on other cars, including BMW V8's & 6's, Merc's and Audi's

Edit: I might also add that alot of the warranty companies wont allow the removal of cats on vehicles that have pre cat and after cat oxygen sensors. If you do, the engine is not covered under the warranty.

Edited June 23, 2009 by *Glenn*

[CamB 48]

It seems to me it would be retarded to have the second sensor giving input into the fuel trim (simply because cats can clog, and because I really can't see any benefit), but just because its retarded doesn't mean that manufacturers don't do it for some reason I can't fathom.

Which is why I am being cautious.