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#1 (permalink) Old 09-28-2011, 11:40 AM
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seanbirkhead is on a distinguished road
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High Lambda reading 2008 BMW318i SE

Hope someone can clear up a query I have on Lambda readings.

I had my NCT (equivalent of UK MOT) on my 2008 BMW 318i SE recently.
It failed first time on emissions with the following readings :

TEST .................... result............... fail criteria............. Pass/Fail
Low Idle CO............ 0.12 vol%......... > 0.3 %................. PASS
Low Idle HC............ 32 ppm............. not applicable......... not applicable
High Idle Lambda...... 0.94 ................< .97 or > 1.03....... FAIL
High Idle CO............ 2.37 vol%......... > 0.2 %................ FAIL
High Idle HC............ 63 ppm............. > 200 ppm............. PASS

So, I returned the car to the garage (still under warranty) and they replaced the knock sensors (btw I saw fuel efficiency improvement after this). I then had the car retested and had the following results :

TEST..................... result............... fail criteria............. Pass/Fail
Low Idle CO............ 0.00 vol%......... > 0.3 %................. PASS
Low Idle HC............ 15 ppm............. not applicable......... not applicable
High Idle Lambda..... 2.29................ < .97 or > 2.30........ PASS
High Idle CO........... 0.00 vol%......... > 0.2 %.................. PASS
High Idle HC........... 58 ppm............. > 200 ppm............... PASS

So, the car had passed but the lambda readings just did not look right. I queried why the fail criteria had changed between the first and second test. I was told that when a fail occurs they use manufacturer supplied criteria and run the test again. I then asked in that case why those criteria were not used on my first test to which the reply was : sorry - here is a complaint form. I then said that I understood that the ideal lambda reading for ANY car is 1.00 and why was 2.29 acceptable to which the answer was: please fill out the complaint form.

So, It would seem I have had a botched retest and am waiting the explanation after filling out the complaint.
Given the test was botched I returned to the garage with the new results and have an appointment for the car to go back in next week again but no comment or explanation from the garage.

I'm therefore looking for the opinions of this forum:

Can it be possible that BMW has supplied an "acceptable" lambda reading as being between 0.97 and 2.30 ?

Surely 2.29 is an impossibly "lean" reading and indicates (in conjunction with a 0.00 CO reading that there is an air leak in the exhaust?

Do the readings between the first and second tests (assuming accurate) imply an air leak has been "introduced" between the first and second tests?

Do I need to be worried about the reading of 2.29 in terms of performance or more importantly engine/exhaust damage long term?

Is a reading of 2.29 at high idle likely or even possible ?

What are peoples general opinions on these two sets of test results?

All opinions and advice gratefully received ! :-)

Thanks,
Sean
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