Z3 97 Catalytic Converter

S

Steve76Z3

Newbie
Joined
May 11, 2025
Points
3
Hi,
I’m new to this group today, but have owned my Z3 for 4 years, love my car and now the dreaded MOT has come round again and it failed on the emissions.
I’ve already trawled previous chats on here about other z3 owners who have had the same issue, which has been massively helpful!
Ultimately I’m looking at buying the best replacement Cat on the market and wondering if someone could send me a link for a company one of you guys have used to purchase that has been a success with getting your car through the emissions test?
 
Andyboy

Andyboy

Zorg Guru (II)
Joined
Jun 2, 2019
Points
119
Location
SHEFFIELD
Steve76Z3 said:
Hi,
I’m new to this group today, but have owned my Z3 for 4 years, love my car and now the dreaded MOT has come round again and it failed on the emissions.
I’ve already trawled previous chats on here about other z3 owners who have had the same issue, which has been massively helpful!
Ultimately I’m looking at buying the best replacement Cat on the market and wondering if someone could send me a link for a company one of you guys have used to purchase that has been a success with getting your car through the emissions test?
Click to expand...

If it still has the original BMW cat DO NOT replace it. Chances are the lambda sensor is knackered and a new Bosch one is cheap enough.

Aftermarket catalytic converters are all junk. All of them. You might get one MOT pass out of them but that's normally your lot.

What did it fail on? C.O, Lambda? A high CO reading and everything else OK means the cat isn't much good.
 
S

Steve76Z3

Newbie
Joined
May 11, 2025
Points
3
Andyboy said:
If it still has the original BMW cat DO NOT replace it. Chances are the lambda sensor is knackered and a new Bosch one is cheap enough.

Aftermarket catalytic converters are all junk. All of them. You might get one MOT pass out of them but that's normally your lot.

What did it fail on? C.O, Lambda? A high CO reading and everything else OK means the cat isn't much good.
Click to expand...
 
S

Steve76Z3

Newbie
Joined
May 11, 2025
Points
3
So when I first got the car it had a loud rattle in the cat so I changed it to a cheap replacement cat not realising it would be an issue.
I’m not sure on the reading at the MOT last week, but the guys there always struggle to get the numbers in the green together to pass. I will have at the Lambda sensor to see if that helps. Appreciate that advice!
 
TrevS.

TrevS.

Regular Member
Joined
Jun 30, 2021
Points
9
Hi Steve,I’ve got the same problem,my Mot is due in a month and my cat needs replacing..I’ll do some research and let you know how I get on. Trev
 
S

Steve76Z3

Newbie
Joined
May 11, 2025
Points
3
TrevS. said:
Hi Steve,I’ve got the same problem,my Mot is due in a month and my cat needs replacing..I’ll do some research and let you know how I get on. Trev
Click to expand...
Hi TrevS,
That’s brilliant, appreciate you doing this!
I’m still looking for the right Cat, so I’m happy to let the MOT week expire to get the car sorted properly.
i look forward to hearing from you!
cheers, Steve
 
John_B

John_B

Zorg Guru (II)
Supporter
British Zeds
The M44 Massive
Joined
Jun 2, 2023
Points
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Location
Derbyshire, UK
Model of Z
Z3 2.8 pre-facelift (Izzy)
I too had an MOT failure on emissions and I got this advice which has stuck with me ever since. The ebay link no longer works, however if you do go down the route of replacing your aftermarket cat, it's worth bearing this in mind.

(For the record, I didn't end up replacing the cat. I threw a bottle of Cataclean in the fuel tank and ragged the hell out of the car on the way to the test to get the cat nice and hot. I had a quiet word with the tester too and asked if they'd mind doing the emissions test first. I don't know whether they did or not, but I got a pass!)
1747201016178.png
 
Trevor /chedder

Trevor /chedder

Zorg Addict
Joined
Oct 23, 2021
Points
59
John_B said:
I too had an MOT failure on emissions and I got this advice which has stuck with me ever since. The ebay link no longer works, however if you do go down the route of replacing your aftermarket cat, it's worth bearing this in mind.

(For the record, I didn't end up replacing the cat. I threw a bottle of Cataclean in the fuel tank and ragged the hell out of the car on the way to the test to get the cat nice and hot. I had a quiet word with the tester too and asked if they'd mind doing the emissions test first. I don't know whether they did or not, but I got a pass!)
View attachment 336381
Click to expand...
That was me. The type 3 cat is still going strong.
 
S

Steve76Z3

Newbie
Joined
May 11, 2025
Points
3
This is great! I’ve only seen type2 options but wanted a type3
I don’t mind the cost tbh. People are telling me to scrap the car, but I’m not comfortable with that as I love driving round getting flashed by other z3 legends!
 
Ian&Sue

Ian&Sue

Zorg Guru (IV)
Supporter
British Zeds
The M44 Massive
Joined
Mar 30, 2019
Points
155
Location
North Yorkshire
Model of Z
1.9 Z3
Trevor /chedder said:
Found one. Type 2 is legal but crap as they hardly have any active ingredients, type 3 made to a higher emissions standard and should sort you out. https://ebay.us/m/HwQEFl
Click to expand...
I think the cat in this link is for an M43 not an M44. We had this problem recently & couldn't find a type 3 approved cat for an M44 anywhere so had to settle for a type 2 in the end, time will tell how long it lasts.
 
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