5 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHToo high lambda reading in MOT test
Leading reported evidence
Check exhaust, all looks tight, no leaks
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
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Leading evidence: 'Check exhaust, all looks tight, no leaks' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'k and n was oiling up the old one' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check exhaust, all looks tight, no leaks' (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.
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Performed · outcome unconfirmed
I have changed my MAF to an absolute certain Bosch one and switched back to a standard air filter, as I suspect the K and N was oiling up the old one.
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Discussions that suspect a cause
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Suspected cause
I have changed my MAF to an absolute certain Bosch one and switched back to a standard air filter, as I suspect the K and N was oiling up the old one.
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.
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Suggestion · Original poster
I ordered another tube just in case, but was also think that with all these changes, i maybe need a remap.
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.
5 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
911uk: 1 discussions
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Generation: 20261026T212127Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Hi all, need some leads for root case on MOT fail lambda range .970 to 1.030 - tested at 1.052. reading is high on both exhausts. Lots have changed since last MOT
New IPD intake and GT3 throttle body, new TG 200 cats, Fabspeed mufflers, all 4 new o2 sensors.
Checked exhaust, all looks tight, no leaks
Between the air filter MFS and throttle body, I have a new silicone tube connecting the 2. This never fit well, and even after some trimming, still maybe an issue. Can this be the source of higher `lambda reading' with some air leaking in post MFS? I ordered another tube just in case, but was also think that with all these changes, i maybe need a remap. Any advice?
thanks!
Been struggling with mine also over the last couple of years. Exactly same lamba reading as yours, 1.037 - 1.05 too lean. HC and CO2 all good.
Watching the tester, the readings get better at higher RPMs IE over the 2500 rpm fast idle limit to around 3,000 rpm. Stuffing a rag up the tailpipe helped a bit but ultimately stuffing the probe up another cars exhaust sorted it!!!!
New tester at the garage this year so not feeling confident.
There will be many opinions offered on here, blaming the cats / air leaks / lambda sensors etc. Truth is, nobody seems to have a definitive.
I suspect that the ECU is getting duff info from a sensor. (Lambda or MAF) If the HC and CO2 are ok then cats are working, and / or engine is combusting efficiently, but a little lean.
Or, the exhaust set up is now much less restrictive meaning less fuel is thrown into the engine at idle. But then the pre cat lambdas should tell the engine to trim up the fuel mix.
I have changed my MAF to an absolute certain Bosch one and switched back to a standard air filter, as I suspect the K and N was oiling up the old one.
Waiting till January for the test so crossing fingers. Sorry not more help.
Appears to be a case of throwing cash at parts for it till it works.
:dont know:
My understanding, and I'm happy to be re educated here...
Is that the cat converts NO and CO HO and C into H2O N, and CO2. Ie water nitrogen and CO2. The Cat doesn't have much input on a high Lambda?
Though it's job is to strip off oxygen molecules and then allows the gases to bond into different less harmful gases.
Anidotal info from tester said the new test equipment was v sensitive and the slightest air being sucked back up the pipe could send it high. I imagine an efficient exhaust with large exit pipes that you can't put the probe all the way in due to a 90 Deg bend doesn't help.
The other thing I've noticed is that a dodgy MAF seems to make no practical difference to how the car runs, thus masking a potential problem.
