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200 Series General Forum for the Volvo 240 and 260 cars |
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New MOT. Good emissions. Lambda top end of scale?Views : 853 Replies : 19Users Viewing This Thread : |
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Sep 20th, 2018, 20:02 | #1 |
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New MOT. Good emissions. Lambda top end of scale?
The jam jar, 240 SE B200F LH2.4 has done only almost 120,500 miles so it is not yet run in. It passed the MOT again today. The reported emissions are good.
Fast idle test.I understand the Lambda result is a calculated result, not a reading from the Lambda sensor. 1.04 is apparently an indicator of probable running lean and consequently less efficient cat operation. Which is odd as the actual emissions are diddly squat. I suppose I should look in to this. Can anyone offer me any guidance please? This might be a particularly appropriate time to start using the Gunson Gastester that is in a journey of delivery to me via My Hermes. **** A convenient time to remind myself that my annual jam jar mileage is under 1,000 miles still. |
Sep 20th, 2018, 20:47 | #2 | |
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Sep 20th, 2018, 20:58 | #3 | |
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I took it for a fair mixed roads drive for about 20 minutes on the way to test. Some years ago a tester advised me to get the car well warmed up. But then again it stood for about 20 minutes before being tested. I've just checked last year. The emissions were good but very slightly higher than this year. A second fast idle test was needed last year to get the Lambda calculated result down from 1.117 to 1.010. Perhaps that was not warm enough last year and needed the second fast idle test. I'd like to understand this a bit more and learn to keep an eye on this myself. Are there readings I can take and a calculation I can do to obtain "The MOT Lambda" result? |
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Sep 20th, 2018, 21:22 | #4 | |
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The MOT gets the lambda from a mathematical calculation from the 4 gas readings , you might be able to read it out on a diagnostic machine , although the older the car the less likely this is . However .. as long as your engine light is off you are ok ...
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Sep 20th, 2018, 22:58 | #5 | ||
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I also remember the burn off procedure. There's a revs and volt meter procedure to test that the burn off signal is sent to the air mass meter. I used that test when I was checking my air mass meter nearly two years ago. At that time I did need a new one. Quote:
And I can't get the four gas readings with DIY equipment so I'll stop thinking so much about this. . Last edited by Stephen Edwin; Sep 20th, 2018 at 23:57. Reason: Tiny little insignificant details.... |
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Sep 20th, 2018, 21:16 | #6 |
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It's running lean. Could be a dirty MAF sensor?
The stoichiometric air:fuel ratio is 14.7:1 (by weight). By measuring the unburnt fuel and free oxygen your car's ratio can be determined, then compared to the stoichiometric ratio to give the lambda figure. In your case the air:fuel ratio is 1.04 x 14.7:1, so 15.288:1
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Sep 20th, 2018, 21:19 | #7 |
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Air mass sensors do not get dirty , they draw freshly filtered air over them and every time you turn off the ignition they glow white hot to burn off anything anyway … Too many people "clean" them and ruin them , not wise on a £250 sensor , I have seen 2 destroyed like this in my time ...
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Sep 20th, 2018, 21:27 | #8 | |
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Sep 20th, 2018, 21:30 | #9 | |
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Sep 20th, 2018, 21:42 | #10 |
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How is air mass measured on Volvos without the air flowing over the sensor? (I'm genuinely interested, not being argumentative).
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