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Discussion summary
YOUR RESEARCHMOT emissions fail with Top Gear exhaust, any suggestions?
Leading reported evidence
Install 200 cell cats and lambdas
Performed · outcome unconfirmed
No successful repair reported for this finding.
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Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
I fitted the TG sports back boxes a few years ago but after having trouble getting through the emissions last year, diagnosed as faulty cats, I also fitted new 200 cell cats and lambdas.
MOT emissions fail with Top Gear exhaust, any suggestions?
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Leading evidence: 'Install 200 cell cats and lambdas' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'cats or sensors' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check adaptations' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
I fitted the TG sports back boxes a few years ago but after having trouble getting through the emissions last year, diagnosed as faulty cats, I also fitted new 200 cell cats and lambdas.
MOT emissions fail with Top Gear exhaust, any suggestions?
Install wheel cylinder
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
I've just fitted new wheel cylinder that leaked instantly.
MOT emissions fail with Top Gear exhaust, any suggestions?
cats or sensors
Suggestion or failed attempt
No successful repair reported for this finding.
0
Identified cause
1
Suspected cause
0
Reported fixes
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that suspect a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause
If it's way off you would have to suspect faulty cats or sensors.
MOT emissions fail with Top Gear exhaust, any suggestions?
Check adaptations
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Fault code check , check adaptations and check for exhaust leaks ..
MOT emissions fail with Top Gear exhaust, any suggestions?
Install 200 cell cats and lambdas
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
I fitted the TG sports back boxes a few years ago but after having trouble getting through the emissions last year, diagnosed as faulty cats, I also fitted new 200 cell cats and lambdas.
MOT emissions fail with Top Gear exhaust, any suggestions?
Install tg sports back boxes a few years ago
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
I fitted the TG sports back boxes a few years ago but after having trouble getting through the emissions last year, diagnosed as faulty cats, I also fitted new 200 cell cats and lambdas.
MOT emissions fail with Top Gear exhaust, any suggestions?
Run engine at 1800-2000 rpm whilst stationary outside the
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
I booked in for the first test of the day and ran the engine at 1800-2000 rpm whilst stationary outside the test bay for 6 or 7 minutes , so the cats would be nice and toasty.
MOT emissions fail with Top Gear exhaust, any suggestions?
Test bay
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
I booked in for the first test of the day and ran the engine at 1800-2000 rpm whilst stationary outside the test bay for 6 or 7 minutes , so the cats would be nice and toasty.
MOT emissions fail with Top Gear exhaust, any suggestions?
Coverage and how to read this overview
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
14 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
911uk: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
1 acknowledgements have no verified action link; they do not establish a repair result.
Outcome without a verified action link
The tester who knows the car well tried a fuel additive and took it for a blast to get it hot but no improvement.
Hi all,
I fitted the TG sports back boxes a few years ago but after having trouble getting through the emissions last year, diagnosed as faulty cats, I also fitted new 200 cell cats and lambdas.
Today, the first test with the new set up its failed on emissions. It's not even close with CO bring 0.43%. The tester who knows the car well tried a fuel additive and took it for a blast to get it hot but no improvement.
I phoned TG who asked for a pic of the readings but haven't got back to me yet so I was seeing if anyone had any experience of this and hopefully a fix.
I also phoned Design911 to see if they'd had any faulty lambdas returned, they hadn't but said they do sell the lambda sensor extensions, has anyone fitted these?
Thanks
I am certainly no expert when it comes to aftermarket items but ill just add what i think ..
the standard cats are i believe in the region of 1K cells .. 200 cells are designed to have a faster exhaust gas flow through .. more power i guess but have a far lower surface area and as such will not be as effective in eliminating the harmful gasses a cat is designed for .
They will always be a borderline pass at best ..
getting them very hot is one way ..
Stuffing rags in the tailpipe each side of the gas analyser probe is another ..
Im wondering if there is a slight issue which with normal cats would be fine but as these are borderline then its failing ..
Usual items would be an exhaust leak drawing in fresh air .. or a slight running issue .. check the fuel trim adaptions to see if the car is compensating .
Fault code check , check adaptations and check for exhaust leaks .. post cat lambdas don't affect the running nor the pass/ fail of these .. pre cat ones do but i very much doubt a new sensor pre cat would be faulty .
The correct way to test is measure each bank and take an average of the two .. you can also see if one bank is higher or lower if you measure each bank .
Thanks both,
It's not showing any fault codes but I can see if I can check the adaptions.
The garage are pretty good so I'll drop it back in the week after I've taken it for a proper blast to make sure it's really hot, I'll take some rags with me too just in case!
My 997 only just passed the lamda reading last week, so while the tester was getting the cats warm, I was reading up on it.
Apparently the exhaust breathes in air from the tailpipe, which throws the reading, hence stuffing rags into the tailpipe.
Obviously, make sure the tester has probe as far in as possible.
Obviously, make sure the tester has probe as far in as possible.
a Bit like the Covid test when have to shove a q tip up your nose so far you're tickling the back of your eye !
If it's way off you would have to suspect faulty cats or sensors. I've just fitted new wheel cylinder that leaked instantly. New parts but alas faulty. It does happen.
Just back from the test station and it's passed!
I went straight from a very spirited blast around the Peak District so it was nice and hot. Still took 3 goes to pass though, holding the revs at different levels for different parts of the test but we got it through in the end.
A couple of tests ago my friendly MOT station commented that they had to try a couple of times to get my car through emissions.
That concerned my a bit so for the next test I put a bottle of CataClean
https://www.halfords.com/motoring/e...and-oil-additives/cataclean-450ml-616247.html
into a 1/4 tank of fuel prior to testing and drove the car for the days leading to the test until I had just enough fuel to get me to the test station, before the warning light was likely to come on ( I never, routinely let the level get that low).
I booked in for the first test of the day and ran the engine at 1800-2000 rpm whilst stationary outside the test bay for 6 or 7 minutes , so the cats would be nice and toasty.
Straight into the test bay, no issues with emissions every test since using this process :thumb:
Mine has passed 3 MOT's with 200 cel cats and top gear mild sport boxes and no issues at all.No warming up and no jollop in the fuel tank.It's a mystery why yours has had such an issue with the test.Use a different tester, ask your local Porsche indy who they use.
This is a source reference. Confirm exact model applicability in the original material.
