Idle and Low RPMS - very lean in closed loop!?

[dassaur]

Hi friends
Very much a newby tuner but trying to learn, but I seem to have a problem - when running in CL, my wideband reads really lean at low RPMs.

Car is a 2014 VF commodore (holden), with the L77 6.0 motor running a 218/226/112+2 .600/.600 cam. 11:1 compression ratio.

Previously car was tuned by a well-known tuner a few times over the years and never had any problems.
I've recently added a wideband to get more into tuning and have noticed my car seems to run horribly lean in CL at low RPMS, probably up to around 1500 or so; but the worst by far is at idle where I get a EQ error (CL) of around 14-16%.

I am sure the wideband is good, I put it in place of my rear o2 in my other car and it reads as I expect it to, pretty much never deviating from 0.98-1.02 except for dfco.
It is in bank 2 of the exhaust at the moment, after the cats. I thought there may have been a leak at the bung, but I swapped the rear o2 with the wideband and no difference. Further, when in PE mode the wideband reads pretty much spot on my EQ commanded so I think it's working just fine. It's an AEM UEGO through the OBD port.

I know my VVE table needs a little work, but I dont trust the fuel trims at the moment. Does anyone have any suggestions that I should look into or wisdom for me?
I've attached a short log and the tune.AK VFv3.hpt24-02-05 14-13-05.hpl

Thanks in advance

[blindsquirrel]

If it is in closed loop, and it is as lean as your wideband says, WHY are the trims not adding fuel and correcting the error? You have two narrowbands telling you that the WB is wrong.

[dassaur]

If it is in closed loop, and it is as lean as your wideband says, WHY are the trims not adding fuel and correcting the error? You have two narrowbands telling you that the WB is wrong.

They are actually removing fuel at that low RPM as per log.
So your theory is the wideband is wrong and/or innacurate?

[blindsquirrel]

You have two OE-quality narrowbands who agree with each other, and disagree with the aftermarket owner-installed wideband. It's nothing to do with my opinion one way or the other.

[dassaur]

You may kindly note I didnt say it was an opinion, but your theory, which I appreciate. I was restating for my own clarity.

Following on with your theory, is there any reason why the WB seems correct at higher RPM and at PE, but not at lower RPM?

[07GTS]

think u also need to lower the polling rate on the fuel trims they seem slow set them to the fastest u can which may show more data ur missing

[dassaur]

Fuel trim polling rate set to 1 second (10ms) which is the fastest ive got (when I right click the channel). MPVI3 and scanner v5.

[07GTS]

are u using laptop when scanning or standalone ? should be 0.1 sec for 10ms but if us using standalone it wont poll at those rates only with laptop, anyway something is not right as those obd2 widebands are usually bang on so something isnt correct like power or earths or maby being after the cat is too hot for it as they are usually best before the cats so they can regulate there own temps easier

[dassaur]

Sorry you're right, 0.1s 10ms not 1 sec. I am using a laptop.

I'll try a different ground, but I'm pretty confident in my wiring. As I said it is bang on in my other car.

[07GTS]

or being mounted so far back it could be a air leak that the narrowbands arnt seeing, increasing the rpm just smudges the error as so much more exhaust flow is added it dosnt see the same error as at lower flows, it will throw ur 02 out a little but can u swap the wideband to the front and put the narrow at the back and see if the issue swaps to the narrowband ?

[grubinski]

Sorry you're right, 0.1s 10ms not 1 sec. I am using a laptop.

I'll try a different ground, but I'm pretty confident in my wiring. As I said it is bang on in my other car.

.1 second is 100 milliseconds.

10 milliseconds is **.01** seconds

[dassaur]

or being mounted so far back it could be a air leak that the narrowbands arnt seeing, increasing the rpm just smudges the error as so much more exhaust flow is added it dosnt see the same error as at lower flows, it will throw ur 02 out a little but can u swap the wideband to the front and put the narrow at the back and see if the issue swaps to the narrowband ?

So I should swap the WB for the NB sensor 1? Annoyingly I dont think the NB will reach.
Forgive my ignorance, but if I didnt say anything about the wideband, do the NB o2s look like they are working as expected as per log?

[dassaur]

.1 second is 100 milliseconds.

10 milliseconds is **.01** seconds

Thanks, you are right of course. 10ms/ .01 seconds

[07GTS]

So I should swap the WB for the NB sensor 1? Annoyingly I dont think the NB will reach.
Forgive my ignorance, but if I didnt say anything about the wideband, do the NB o2s look like they are working as expected as per log?

the 02's look like they are working right, yea swap them just for a test would be good then u know if placement is the issue or wideband, as u know the NB is good there if u put the WB there and it reads good u know its placement, if it still reads bad and u look at the NB in the rear spot if thats good there u know its a WB issue

[dassaur]

OK i've sorted this. Turns out both the narrowbands AND the wideband are correct. The issue is the narrowband placement in the headers. The o2 bung is not far back enough to get a good mixture of the 4 cylinders and essentially the NB was reading 2 of them (at least that's my theory). I plugged the o2 bungs in the headers and put new ones around 20cm (8 inches or so) further down the stream. Without changing anything in the tune, instantly the wideband was reading between 0.98-1.02 all through the rev ranges.

Thanks for all feedback and comments.