New MOT. Good emissions. Lambda top end of scale?

[Stephen Edwin]

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.

CO. max 0.3%. reading 0.00%
HC. max 200 ppm. reading 8 ppm.
Lambda. Limits 0.96 - 1.04. reading 1.04

Natural idle test.

CO. max 0.50% reading 0.00%

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.

[Clan]

Originally Posted by Stephen Edwin

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.

CO. max 0.3%. reading 0.00%
HC. max 200 ppm. reading 8 ppm.
Lambda. Limits 0.96 - 1.04. reading 1.04

Natural idle test.

CO. max 0.50% reading 0.00%

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.

It could have been the lambda sensor not fully warm , always best to give the engine a good workout for 20 minutes before a MOT , Good set of figures though , no problems ..

[Stephen Edwin]

Originally Posted by Clan

It could have been the lambda sensor not fully warm , always best to give the engine a good workout for 20 minutes before a MOT , Good set of figures though , no problems ..

Thanks. That's encouraging re those results.

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?

[Zebster]

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

[Clan]

Originally Posted by Zebster

It's running lean. Could be a dirty MAF sensor?

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 ...

[Clan]

Originally Posted by Stephen Edwin

Thanks. That's encouraging re those results.

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?

a work out is doing over 4000 rpm under load , say up a hill for a period of time it burns carbon from the exhaust front pipe and lambda sensor ..

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 ...

[Zebster]

Originally Posted by Clan

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 ...

I've seen plenty of dirty ones, admittedly not on a Volvo. Our MR2 roadster has needed cleaning several times and is generally a commonly-reported problem. Air filters only remove particle sizes in a certain range, plus fumes tend to pass through and plate out on the sensor.

[Clan]

Originally Posted by Zebster

I've seen plenty of dirty ones, admittedly not on a Volvo. Our MR2 roadster has needed cleaning several times and is generally a commonly-reported problem. Air filters only remove particle sizes in a certain range, plus fumes tend to pass through and plate out on the sensor.

fumes don't go through the Air Mass sensor on volvos , anyway the self cleaning function makes it un necessary and highly risky .

[Zebster]

Originally Posted by Clan

fumes don't go through the Air Mass sensor on volvos , anyway the self cleaning function makes it un necessary and highly risky .

How is air mass measured on Volvos without the air flowing over the sensor? (I'm genuinely interested, not being argumentative).

[Clan]

Originally Posted by Zebster

How is air mass measured on Volvos without the air flowing over the sensor? (I'm genuinely interested, not being argumentative).

The crankcase fumes go into the air intake down-stream of the Air mass meter .. all that goes through the air mass meter is fresh filtered air , the pipes are always clean when you change an air filter .