Had MOT yesterday, it passed , but just scraped through on emissions for lambda.

Emissions were:

HC = 5ppm
CO = 0%
Lambda = 1.029

With limit on Lambda being 1.030 it was a bit close.

I was just wondering what lambda actually is?

I suppose I also want to know what I might help to get it back down a bit (but I don't want to put the centre Cat back in!).

Cheers guys.

 

Lamba is the fuels and air mix, sounds like your car is running a little rich,
Lamba 1 is a perfect burn, anything below that and its running lean (risk of a hot combustion chamber and detonation)
Above Lamba 1 and the engine is running to rich, ( could cause bore wash)
Hope that explains it

 

Lambda value is the amount of oxygen in the exhaust which indicates the air/fuel ratio. Lambda 1 equates to 14.7:1 The cat is obviously working ok to give you zero Co and just 5ppm hydrocarbons.
You may want to check the MAF signal?
JohnD

 

i thought the purpose of the lambda or O2 sensor was to find out if the engine was currently running rich or lean, and adjust it for its next cycle? so if on one cycle it was too rich, it would adjust the amount of air to make it back to what it should be again?

 

As John said,

It will work within different parrameters on closed throttle, it may be getting mis-infomation from another sensor, IE, the MAF sensor as john said, Below is a piccy of the wiring on a MAF sensor,
DONT TRY AN OPEN THROTTLE TEST THOUGH, lol

 

the penny drops


i get it now, so what your saying is that it may be getting a mis reading from the maf sensor so it cant adjust the mixture accordingly?

 

Thanks guys, this is helpful info.

I also have a prodrive ECU, which I have heard can lead to a rich mix, so this may explain it?

Was told when the car was on a Dastek rolling road a few weeks ago that I was running rich.

Replaced the MAF about a year ago, so it could be time for a new one, but I hadn't intended on getting the emissions checked again so I wouldn't know if that had cured it till next MOT.

Had been thinking about putting old ECU in and getting it mapped, could that help the air/fuel mix and hense my lambda reading?

Thanks again!

 

In laymans terms,

If A+BxC= 72 it will performea certain task,
But if A+BxC= 146 it will try and do something else,

A,B and C are sensors,

If that helps get your head round it a little better

 

ADS 78

caning it on a rolling road the ECU moves over to "closed loop" and ignores the lambda sensor and reads fuel / boost / ignition etc from an internal map. it's this map that mappers play with if the car is running rich.

pootling about and at idle the ECU calculates everything "on the fly" from the MAF and lambda trying to get the magic stoichimetric fuel air ratio (lambda = 1).

shaun

 

By way of an update ...

I changed the MAF last week (did the umplug MAF whilst engine is ticking over to test that it stalls (it didn't) test) and took her back to Kwik Fit today to get the emissions done again.

Lambda reading was much better, around 1.009 with engine at c3000rpm and closer still to the magical 1 at idle.

Not sure I need to do anything more now. Still running a little rich, but no surprise there I suppose!

 

Greater than 1 is lean....duff gen from RB#5183.....less than 1 is rich.

There are a number of perfectly good reasons why the Lambda may have been reading slightly lean for the few seconds of the first reading, most of them nothing to do with the MAF at all, like purge valve just opened and with an empty can for example...