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Closed loop lambda for emissions test - using wideband sensor


M1tch
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Hi all,

Just working on my mapping in terms of ensuring that I am able to pass the UK MOT emissions test - which tests CO, HC and Lambda - Lambda needs to be at 1, plus or minus 3%.

I have a single wideband O2 sensor which I have set to run as auto fuelling compared to the AFR table.

I have learnt that the main cat would usually need the fueling to dither between rich and lean as this increases the efficiency of the cat.

https://www.crypton.co.za/Tto know/Emissions/catalitic_converters.html

I know with the auto fuel option with the wideband sensor the fuelling starts with whatever is on the main fuelling table and then gradually adjusts to that target.

The stock narrow band sensors dither around a lambda of 1 - going rich then lean in cycles which makes the cat work as expected.

Question is - is there a way I can set the CLL to dither using my wideband sensor? I can see that I can set wideband and Stoich rather than auto, would this dither or could I set the CLL to the narrowband option?

Last year I had to plug the stock ECU back in again to get past the emissions - my setup has the O2 sensor pre cat with the emissions test being done at the exhaust pipe end with about an 8% drop in AFR pre and post cat, I tuned it to sit at 1 at the engine but was leaner at the test sensor in the end of the exhaust.

Really need to ensure I have everything in place for next year as I don't have an option to run the stock ECU on my engine anymore and there must be a way to allow me to run the Link ECU and be able to pass emissions.

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there is a certain amount of dithering inherent to the circuit due to the length of the exhaust between the combustion chamber and the sensor. there is lag between the injector and the sensor so the closed loop is naturally in a state of oscillating, the closed loop tuning is there to dampen the oscillation. the dithering (oscillation) is most pronounced at slower exhaust speeds (idle).

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Thanks for the responses so far - I will only be running a single wideband O2 sensor for the engine - I can see that the changes per second for fuelling in CLL is set higher at lower RPMs. I have previously upped it slightly however I found if it made is really erratic as the fuel correction was changed quicker than the mixture was changing so the idle wasn't stable!

I guess the question is - have others passed the emission test with just a wideband O2 sensor running CLL? I have a feeling there must have been!

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3 hours ago, dx4picco said:

that is true, but retarding it too much (past 0°) will worsen significantly the combustion efficiency and the combustion itself will reject way more HC and CO and that me be counter productive ;)

Of course -- everything in moderation.  I was lucky enough one time to have the state run emissions testing station near me allow me to make changes on the spot to the tune until it passed (they weren't busy that day).  

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11 hours ago, Adamw said:

Use either of the Stoich closed loop modes, they were designed for cat/emmisions use and have a 0.02 lambda dither built-in to the control logic (ie the lambda with dither +/-0.02 La either side of the set point)

Perfect, thanks Adam, I figured if I set it to Stoich wideband it would work as per OEM narrowband otherwise there would be no real reason to have this option for wideband as you would just use auto.

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I don't see a point why not using automode. Properly tuned CL Lambda control does easy pass the test (give the cats are okay). I do that all the time.  

I wrote a thread with CL Lambda settings a while ago if you search the forum. However start with upfate rate of 1-3 and gain table =5

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  • 5 months later...
On 12/6/2020 at 2:52 AM, mapper said:

I don't see a point why not using automode. Properly tuned CL Lambda control does easy pass the test (give the cats are okay). I do that all the time.  

I wrote a thread with CL Lambda settings a while ago if you search the forum. However start with upfate rate of 1-3 and gain table =5

Thanks for this, I might see if I can book in an emissions test with the garage just to check things are correct, I have just changed injectors over so am reworking the fuel table. I seem to have things sorted in the right sort of ball park though, have set the update rate to be at 4 which seems to give a stable correction of a few % in the idle part of the map.

Need to run the car at higher RPMs to make sure the lower load higher RPM parts of the map are close enough as well.

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