Interpreting M3DK Lambda readout

[garyo]

This may be an old question, but the archive 'search' is switched off at the moment...

 

I've been looking at the motorway cruising sites on my fuel map, and getting a passenger to monitor whether they're rich/lean etc. The lambda readout is strange, and I'm wondering whether it can be relied upon at all. In most cases it reads around 5 or 6 bars into the green, which seems too rich... if it's leaned off, it approaches two bars into the green, and then starts 'strobing' between only two of the red bars (lean) being lit, and 3 or 4 of the green bars being lit. The frequency of the strobing is around once per second.

 

Does this mean I might have some kind of air leak in the exhaust, or is this normal behaviour? Can the lambda sensor be used for this kind of tweak, and should I even bother - or just switch on 'closed loop' mode?

 

Thanks,

 

Gary.

[16vastra]

you ideally want (at least) 3 green bars on this readout

and i have found that a small fuelling change makes the readout dive into the red. not really the fault of the readout or anything, its just the yellow area is very narrow voltage wise, so its more of a sensor accuracy problem.

if you cant get it to sit @ 3 greens i would be happy enough with 5 mate. little added safety margin and all that.

you also wanna make sure the sensor is ok, is it a nice new decent quality one? the readouts only gonna be as accurate as the voltage its seeing.

 

this is why i prefer my mbe with its data logging

[Peter Carmichael]

Concur with 16Vastra. The scale is not attempting to tell you "how rich" the engine is. It is just attempting to show rich or lean. A small fuelling change will make the graph dive to the left.

 

The sensor is normally used for running closed loop and the ECU cycles the fuelling through rich and lean so it keeps crossing and recrossing the accompanying voltage jump from the sender. The output cannot be used to determine air/fuel ratio with any accuracy but can keep you safe from over lean fuelling.

[Peter Carmichael]

Concur with 16Vastra. The scale is not attempting to tell you "how rich" the engine is. It is just attempting to show rich or lean. A small fuelling change will make the graph dive to the left.

 

The sensor is normally used for running closed loop and the ECU cycles the fuelling through rich and lean so it keeps crossing and recrossing the accompanying voltage jump from the sender. The output cannot be used to determine air/fuel ratio with any accuracy but can keep you safe from over lean fuelling.

[Chris W]

The lambda sensor is essentially a switch which should be in one state or the other. The reason you are able to see anything in the yellow at all is that the characteristic of the switching is not perfect and there is a small slope to it, so that it appears you can "catch" it between states.

 

In reality this slope is still tiny so a small adjustment can see the readout dive one way or the other.

 

Chris

 

1.8K SV 140hp see it here

[garyo]

okay - I think I understand now. So ideally I want to lean off until I start jittering between rich and lean, and then add 3 or 4% of fuel to be safe?

 

If I buy a wide band sensor, will this work with the ECU without modification?

 

Cheers,

 

Gary.

[16vastra]

not really as it is 0-5v and not the standard 0-1v so you will need a separate map to convert the voltages

which is a git

 

i am using (well, its not mine, gotta buy my own soon lol) a bosch lsm11 sensor from www.lambdasensor.com (130 quid) which is a halfway house - accurate at rich mixtures, but still 0-1v and should work fine in place of a standard sensor.