Lambda reading at MOT test
Discussion
Just my Porsche Boxster MOT'd. During the emissions test, The Lambda reading came out at 1.03. The limits are 0.97 to 1.03. The tester showed this as a fail. I looked on the gov website and the book states between 0.97 and 1.03. Surely 1.03 is a pass.
Anybody else experienced this
Grateful for any input
Thanks
Anybody else experienced this
Grateful for any input
Thanks
If you are unhappy with the result & can't resolve it with the garage complain to DVSA. Note the last line in the quote which might be rather problematic if you need the car as your daily drive. No guarantee that it won't do the same on the DVSA retest.
https://www.gov.uk/getting-an-mot/problems-with-yo...
"Appeal if your vehicle failed an MOT
You need to discuss your test results with the test centre before anyone starts repairs.
You can appeal against the failure if you think it’s wrong. Fill in the complaint form and send it to DVSA within 14 working days of the test.
DVSA will contact you within 5 days to discuss your appeal.
If DVSA decides to recheck your vehicle, you’ll need to arrange a date and pay the full test fee again. They’ll send you an inspection report listing any vehicle defects.
You should not have any repairs made until the appeal process has finished."
https://www.gov.uk/getting-an-mot/problems-with-yo...
"Appeal if your vehicle failed an MOT
You need to discuss your test results with the test centre before anyone starts repairs.
You can appeal against the failure if you think it’s wrong. Fill in the complaint form and send it to DVSA within 14 working days of the test.
DVSA will contact you within 5 days to discuss your appeal.
If DVSA decides to recheck your vehicle, you’ll need to arrange a date and pay the full test fee again. They’ll send you an inspection report listing any vehicle defects.
You should not have any repairs made until the appeal process has finished."
paintman said:
If you are unhappy with the result & can't resolve it with the garage complain to DVSA. Note the last line in the quote which might be rather problematic if you need the car as your daily drive. No guarantee that it won't do the same on the DVSA retest.
https://www.gov.uk/getting-an-mot/problems-with-yo...
"Appeal if your vehicle failed an MOT
You need to discuss your test results with the test centre before anyone starts repairs.
You can appeal against the failure if you think it’s wrong. Fill in the complaint form and send it to DVSA within 14 working days of the test.
DVSA will contact you within 5 days to discuss your appeal.
If DVSA decides to recheck your vehicle, you’ll need to arrange a date and pay the full test fee again. They’ll send you an inspection report listing any vehicle defects.
You should not have any repairs made until the appeal process has finished."
That's the problem above - you're caught by the short and curlies if you want to use the car.https://www.gov.uk/getting-an-mot/problems-with-yo...
"Appeal if your vehicle failed an MOT
You need to discuss your test results with the test centre before anyone starts repairs.
You can appeal against the failure if you think it’s wrong. Fill in the complaint form and send it to DVSA within 14 working days of the test.
DVSA will contact you within 5 days to discuss your appeal.
If DVSA decides to recheck your vehicle, you’ll need to arrange a date and pay the full test fee again. They’ll send you an inspection report listing any vehicle defects.
You should not have any repairs made until the appeal process has finished."
The thing that worries me is that the emission test equipment is only required to be calibrated every 6 months - In the industry (ie test labs in car manufacturers) it's done at least once a day. Having said that I think (even though most are just kicked around the floor in MOT stations!) They tend to be generous. I've had 2 petrol cars show up as zero CO (non-cat cars as well). I asked the tester if I could get a free VED
Strangely he blindly trusted the equipment - I wasn't going to argue.Sorry, I should have been clearer, when I said tester, I meant the equipment displayed red at 1.03 indicating fail, the MOT tester man, gave me the benefit of the doubt.
On the gov web site it states 0.97 to 1.03 as the limits, although it states BETWEEN these figures. As an engineer I would include these figures at the limits. I cant seem to find whether 1.03 is pass or fail, although the equipment indicates fail. Not very clear.
On the gov web site it states 0.97 to 1.03 as the limits, although it states BETWEEN these figures. As an engineer I would include these figures at the limits. I cant seem to find whether 1.03 is pass or fail, although the equipment indicates fail. Not very clear.
Big Rumbly said:
Sorry, I should have been clearer, when I said tester, I meant the equipment displayed red at 1.03 indicating fail, the MOT tester man, gave me the benefit of the doubt.
On the gov web site it states 0.97 to 1.03 as the limits, although it states BETWEEN these figures. As an engineer I would include these figures at the limits. I cant seem to find whether 1.03 is pass or fail, although the equipment indicates fail. Not very clear.
Hmm - I thought if the equipment showed a fail then the human tester's hand were tied. I agree with you regarding between .97 and 1.03.On the gov web site it states 0.97 to 1.03 as the limits, although it states BETWEEN these figures. As an engineer I would include these figures at the limits. I cant seem to find whether 1.03 is pass or fail, although the equipment indicates fail. Not very clear.
If the machine says fail then it's a fail. If the machine says pass it's a pass. There are always two copies of the emissions sheet printed on a petrol test. One for the customer and one for the garage who must keep it for at least three months.
Lambda is measured to 3 decimal points during the test. For Bet test limits 1.030 is a pass, 1.031 is a fail. Likewise, 0.970 is a pass, 0.969 is a fail.
If it fails the BET test then a full cat test must be carried out using the manufacturer's specified limits before a fail should be issued. The manufacturers limits can be different from the BET test. Some lean burn BMW engines can have a lambda value of over 7.000
Lambda is measured to 3 decimal points during the test. For Bet test limits 1.030 is a pass, 1.031 is a fail. Likewise, 0.970 is a pass, 0.969 is a fail.
If it fails the BET test then a full cat test must be carried out using the manufacturer's specified limits before a fail should be issued. The manufacturers limits can be different from the BET test. Some lean burn BMW engines can have a lambda value of over 7.000
OP, if you are asking about the way the numbers are judged I'd agree with the answers above, if you are wondering why your car was around the limits on lambda the most likely answer is the test method being marginal rather than the car.
If your car has the common twin-pipe setup there's a risk of oxygen from the second pipe "contaminating" the sample, even a very small amount could cause the reading you are reporting. Sticking a rag up the pipe that doesn't have the probe in it increases the flow rate through the tested side and would very likely result in a clear pass.
If your car has the common twin-pipe setup there's a risk of oxygen from the second pipe "contaminating" the sample, even a very small amount could cause the reading you are reporting. Sticking a rag up the pipe that doesn't have the probe in it increases the flow rate through the tested side and would very likely result in a clear pass.
Steve H said:
Sticking a rag up the pipe that doesn't have the probe in it increases the flow rate through the tested side and would very likely result in a clear pass.
I'm not convinced by the theory of cross-contamination between the tail pipes since they should both have the correct gas mix. However, a common cause of an excess lambda reading is an exhaust leak allowing air to be pulled in, so adding back pressure could cover that.GreenV8S said:
I'm not convinced by the theory of cross-contamination between the tail pipes since they should both have the correct gas mix. However, a common cause of an excess lambda reading is an exhaust leak allowing air to be pulled in, so adding back pressure could cover that.
Yes, they should but at relatively low gas speeds on a fairly large capacity engine with large diameter tail pipes it's quite likely that some air will be getting in as well as getting out. For a marginal fail it could be the answer but I agree that any kind of small leak could have the same effect.Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff