How weak is a lambda reading of 2 at idle?

 

That value has no meaning in any terms

 

eh? course it does. it's an AFR of 28:1 rather than lambda = 1 of 14:1

that's very weak, i doubt it would run at such a weak mixture

 

okey doke,

Well i've just had an exhaust probe stuck in my exhaust pipe just to check the AFR (if thats the correct terminology) and on idle it settled at around lamda 2.0x then went to lamda 1.2x at 2500rpm.

Hope it makes a bit more sense now, or am I still talking drivel?

 

If thats the case it wouldnt run and you couldnt measure it.

 

I reckon he is talking CO % NOT lambda.

 

I think he is talking about sausages.

1 sausage = 7.35:1 AFR

2 sausages = 14.7:1 AFR

1.2 sausages = 8.82:1 AFR




I prefer my sausages explanation but yes he is probably talking about CO %.

 

so do i, but lambda = 2 still has a meaning and can be measured

 

Come on you bunch of amateurs!! Give the guy some proper advice!!

It depends on what type of probe is used. If it's a proper Exhaust Gas Analyser, where the probe goes fairly deep into the tailpipe and you are seeing Lambda 2.0 then there is a problem.

However, if it isn't it could be as simple as a draft into the tailpipe affecting the reading. Especially if this is on a Dyno with the fan running.

An exhaust leak would also cause this.

 

Thanks for the reply Christian. This was a probe placed only a few cm's into the tailpipe.

The guy who measured it (ex WRC Hyundai Technician) said we'll do a more comprehensive test once he's got a new clamp for the exhaust probe, on Tuesday of next week, so should hopefully see some results that are a bit more realistic.

 

lead_foot PMSL

foreigneRS
Show me a petrol car running with a lambda of 2.0 and as there is
no mention of any bad running or incorrect measurement methods
all my answers are valid.


Christian and Beccy,
My advice given in simple terms of the question asked.



All makes me wonder why I even bother to help anyone anymore.



P.S. You are all coooooooooonts

 

PMSL

 

Phil,

I will always be around to help you

 

...evidently..i am flattered you waste time and money on me..unless its free

 

Evidently .... ??????

Please elaborate Phil

 

maybe?!

 

AlexF,

I can only assume that isnt a petrol car as I dont recogniose it ?

 

Mitsubishi Galant. Probably with a 2.0 GDI Petrol engine. Fuck knows the significance of it though!!

 

I though mitsi's were gas guzzlers

 

Why has nobody come up with what is probably, 95% certainly teh simplest and correct answer.

This is about what you will get if you probe a car with a fully warmed up and active CATALYTIC CONVERTOR fitted.

Totally pointless reading a car with a catalyst unless its to ascertain that its working, which this one seems to be. lol

 

Hmmm... missed this, so now i doubt this simple fact has been overlooked.

 

its always simple when you think about it,,,, and i didnt think about it

 

Stu, what I meant was that the test he did was with the car sat on idle and stationary because he had no way of securing the probe to the exhaust, and once he gets a new clamp, we'll give it proper test, through the gears and full rev range

 

What car is it?
Does the car have a catalyst fitted or not?

 

Thats because we (I) assumed it was a shonky old ford.
You have to admit, the initial question isnt exactly loaded with info.

 

I don't understand Stu
I didn't think catalytic converters changed the lambda reading, only removed the CO and HC
even if it had a huge exhaust leak,
there is not a gas analyser on the market that can read as far as lambda 2 .....


or is it different with oxygen sensors in the exhaust, does the cat remove oxygen?
I don't know about that, only about gas analysers..

(If so, then the idle lambda should be measured with a gas analyser not an oxygen sensor)

 

The whole composition is apparently changed and whilst i dont understand the checmical dynamics of the modern three way system, i do know from experience that you cannot accurately read the gases after a catalyst. On modern turbocharged cars the catalysts fitted are so impressive you cannot read more than about lambda 1, even flat out at 350bhp. Whilst this is a great achievement, it makes a simple setup and chip a real ballache.



Lambda 2?
A decent one like mine will read down to lambda 10.
http://www.labcell.com/product.asp?id=17&pr=46


A Gas analyser is no better with a catalyst. The fact remains to see what an engine is producing you must look BEFORE the catalyst. Thats why, as mentioend earlier, the lambda sensor on a production car is always located BEFORE the catalyst.

 

Its a GDi

They run lean on purpose



With a CAT you should still be able to measure Lamdba.... Even MOT test gear does that? I have I misunderstood?


Alex

 

AlexF,

It will read lambda after the gas transformation.

Which is NOT the same as reading lambda before the cat

 

Correct, that i suppose is a FAR clearer way to put it than i did.

 

Stu that's what I'm saying, what you have is not a gas analyser
a true gas analyser will measure the same afr after a cat. as what's produced in the engine
I thought they may have been using a gas analyser (like in an Mot station or most garages) but I guess it wasn't, just a lambda gauge

I think Alex F understands what I'm getting at

 

Yes that is true....

Hence most cars now have pre and post cat sensor to check the Cat is working for OBDII.

But you could get a car running on lamdba 2.


Alex

 

AlexF,

Yes but ONLY after the cat

 

Just for a sake of somthing to do I'll waffel on about how cats work!

The process that a catalyst uses is based on 2 opposite chemical processes;

• Oxidation- where a substance combines with oxygen
• Reduction- where a substance releases oxygen.

The use of precious metals; platinum, rhodium and palladium convert the pollutants into non toxic gases.

3 way catalytic converters are the most common and fitted to all new petrol engines.

The gasses effected by the cat are CO, NOx and HC.


You get rid of CO by ADDING O2 (oxidation)
You get rid of HC by ADDING O2 (oxidation)

But of these conditions you achive by running the engine a tinyt bit lean (excess o2 in the exhaust gas).

NOx you get rid of by SUBTRACTING 02 (reduction).

To achieve this the exhuast needs to be low in O2, so you run the engine slightly rich.



This is why is you scope a lambda sensor you get a trace like this....

http://www.picotech.com/auto/wavefor..._zirconia.html

 

Sorry, i missunderstood what you were saying there and your right of course.

I disagree, a normal MOT gas analyser wont read the same wether tested before or after a catalyst at all, sadly i dont have all day to argue this point as i am rammed busy, but i am quite sure the argument will rage on.

 

discussion stu

 

I hate it when my keyboard does that!!

 

With a lean burn engine a pre cat lambda reading of 2 would be possible.... In fact if the engine is running that before the cat I wouldn't expect it to change much after the cat

As an AFR is lamdba 2 about 30:1 ??

Alex

 

AlexF,

As I said above, the original question didnt exactly have all the info and I and
others made many assumptions.

A petrol engine wont run on a lambda of 2.0 which was my original point.
The fact a cat can alter the output exhaust and that is measured is
another point entirely.

Talk about a can of worms

 

SECS there are petrol engines that will run on an average mixture of lambda = 2 and have been for many years

just that they normally have a localised mixture at the spark plug closer to 1