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Fluctuating AFR - closed loop doesnt seem to correct


r33lew

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So, my car is an R33 GTR RB26

It made 620 on a hub dyno, has tomei type b drop in cams, single turbo ect. Its running a standard intake plenum with aac and iac still fitted.

Im using a G4x with a motec lsu (lambda to can) 

When i first got my car back i was surprised with how lumpy and rough it idled. Ive got a tablet with pclink constantly on display, when i switched over to 'lambda' layout it was floating about 12 afr and target was 14.6 at 80°.

After a visit back to my guy who mapped it, it was discovered CLL wasnt switched on. But before switching it back on, the afr seemed to keep returning after being corrected manually, and then occasionly fly up to 17s..

We figured this is an issue with my car not the map.

So cll was switched back on with +/-20% correction 

But after returning home it seems its bahaving the same, now whilst it sits at say 13 afr ive tried switching cll on / off and no difference is made.. 

 

Ill pop a link for two logs, one is where i start the car from cold and let it idle up to 80° and one is me switching cll off then on.

https://easyupload.io/m/d39955

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It appears to be working correctly to me.  You might have to give more info about why you think it isnt working correctly, and maybe attach your tune so we have some context. 

Your cold start log below, I will make a few comments to describe why I say it appears to be working correctly.  

At the lefthand end of the log, shortly after starting the lambda (dark blue) is sitting quite a bit above the target (yellow trace), closed loop lambda is disabled at this point because your ECT is below the set lockout.  It remains running quite lean with CLL disabled until just after the 2:00 time mark, here your coolant temp reaches the set lockout and CLL enables.  You can see right away CL fuel correction is ramped up (cyan trace) and the lambda comes down and sits right on top of target for the rest of the log.  The cyan trace shows how much fuel is being added to make the lambda reach target.  

k66piL7.png

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To be honest, i agree, the log i got was poor, i should of waited until the problem was more obvious, i will go for a drive later tonight and get it to sit way off target on idle, and i will log it then. Is there anything i should do or interigate, settings wise?

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7 hours ago, r33lew said:

Is there anything i should do or interigate, settings wise?

I wouldnt suggest any changes until you have something that shows us the problem occurring.  The "CL Lambda Status 1" as shown above will be the first thing to look at when you think there is a problem, this will tell you the reason it is disabled or if it has reached the clamps etc.  

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  • 2 weeks later...
On 9/2/2022 at 10:11 PM, Adamw said:

I wouldnt suggest any changes until you have something that shows us the problem occurring.  The "CL Lambda Status 1" as shown above will be the first thing to look at when you think there is a problem, this will tell you the reason it is disabled or if it has reached the clamps etc.  

sorry for the late delay, only just managed to get out, here is a short log of the car idling when i pulled over, ide say it was idling for 20 seconds before i logged and stayed like this.

ccl not working.llgx

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Can you attach a copy of your tune.  CLL is trying to work, you can see it is pullng 13% fuel out at the beginning of the log and is down to -17% at the end of it.  But lambda hasnt changed much so it suggests there is something else going on - possibly minimum PW clamp or something.  

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36 minutes ago, Adamw said:

Can you attach a copy of your tune.  CLL is trying to work, you can see it is pullng 13% fuel out at the beginning of the log and is down to -17% at the end of it.  But lambda hasnt changed much so it suggests there is something else going on - possibly minimum PW clamp or something.  

Ill send you a direct message adam. Thanks for looking.

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Ok, I had a quick look at your tune.  Some of the problem is due to a mistake in your deadtime table, the rest of it is just due to the CLL being set up to use the basic "stoich mode" with the lowest gain possible - it means it is very slow to react to changes.  You could try increasing that gain - around 5 would be more typical, but changing to the auto mode would give much better control.  

It seems that possibly the fuel tune is quite a long way off too.  In that last log the CLL is pulling 17% fuel out at the end and the lambda is still 15% richer than target.  

KD3HrHs.png

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10 hours ago, Adamw said:

Ok, I had a quick look at your tune.  Some of the problem is due to a mistake in your deadtime table, the rest of it is just due to the CLL being set up to use the basic "stoich mode" with the lowest gain possible - it means it is very slow to react to changes.  You could try increasing that gain - around 5 would be more typical, but changing to the auto mode would give much better control.  

It seems that possibly the fuel tune is quite a long way off too.  In that last log the CLL is pulling 17% fuel out at the end and the lambda is still 15% richer than target.  

KD3HrHs.png

Thanks adam, ive got a good log now with the afr changing. This is with CLL turned off the whole time.

I pulled over 3 times, the first and last time the afr was on target but the second time was off. Sometimes it goes rich, sometimes lean.

So with the dead times... when my car was mapped it was overcharging at like 16v.. once i fixed this my tuner said hell amend my dead times.. im guessing he just adjusted the 13v value.

So as you suggested dead times, i read them along with battery votage and my afr/target.. they all seem to marry up, almost like when my car is charging .1v lower it sits at a different afr.. ill attach a screenshot below and a link to my log.

So grateful for your time adam!

https://easyupload.io/ii8z88

LINK ABOVE

20220914_211702.jpg

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Quick appreciation post @Adamw i ammended the dead times to suit asnus data sheet, and the car sits at a steady afr now.

I tried auto CLL mode but it didnt seem to react as fast as stoich, maybe i have the settings wrong.

ive also moved idle target to 13.9 as the car runs so much smoother on idle.

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