IDLE AFR fluctuations

[maudyZ28]

Hi All,

Well got my wideband in and done a OLSD tune and used auto VE etc. Then corrected and applied it and also for DD re-enabled DFCO.

My question is that my AFR at idel fluctuates, so when starting from cold when commanding about 14.2 the WB reads 15.2, i know the VE is correct as when driving it is pegged at 14.6-14.7 mostly and BEN are around 1. Whan seems to happen is that when driving for a while the idle then is richer than commanded so now commanding 14.63 and runnig 14.0 ish +/-0.2, but then after I drive a bit more and stop again it might be 15.0??

I dont understand this fluctuation, I have logs I can post and my tune, but I dont even know why it would run commanded, then leaner, then richer all at idle??

will post logs at when home :D

thanks

[Aloicious]

there are alot of factors that come into play with idle tuning. are the variations happening in the same VE cell while running in OLSD? is the rich/lean issue happening on the same drive, or does it swing one way then another after restarting? what are the vehicle specs?

it could be anything from heatsoak or other temperature variations, to atmospheric conditions, even possibly unpredictability in the injector characteristics, spark variations, the list just goes on from there.

have you done a RAFIG to get your desired airflow table in line?

post up your tune and log that is run with that tune and it could help out a bit.

[maudyZ28]

The car is stock internals, 99 camaro A4 with LS6 intake, SLP lid, 1 3/4 LT headers into 3" true duals, de catted on the engine front

I've only done VE table when driving, not messed with any idle tables or anything as the car idles fine just the AFR fluctuates. The tunes before and after are below, and the log. (still need a bit more logging on VE to get all cells to match)

I have come to think however the fluctuation may not be real and infact be due to slow gas flow?

[Aloicious]

do you have stock injectors in it?

I'm not sure what you mean by 'slow gas flow'

[maudyZ28]

nope, they are 2002 injectors and I have adjuated table accordingly

I mean slow gas flow in exhaust past sensor at idle thats all, even narrow bands dont fluctuate up and down here like when driving

[Aloicious]

ah okay.

I've been busy at work, I'll try to take a look at the tune/logs soon.

[maudyZ28]

yeah no probs dude, thanks. Not much to see. Just wondered if anyone had any idea why it is doing it and then settles to be ok. Think it could also be heat soak? as it does it more when I restart it when hot. It's still a work in progress though, as all tuning is :D

[5.7ute]

yeah no probs dude, thanks. Not much to see. Just wondered if anyone had any idea why it is doing it and then settles to be ok. Think it could also be heat soak? as it does it more when I restart it when hot. It's still a work in progress though, as all tuning is :D

Make sure you log IBPW as well as DYNCYLAIR.DMA to compare when the AFR's are different.(I use a calc pid for DYNCYLAIR to get more precision) You should even look at logging battery voltage, manvac, injflow & dynamic airtemp to see if there is a variation there that could be the issue.
Heatsoak if evident is not something you can accurately tune around IMO. The best fix is to try & eliminate it.

[SSpdDmon]

IMO - idle AFR's will fluctuate from commanded primarily due to temperature variation in IAT's and ECT's (as will your AFRs when driving). Unless we develop a custom, single-column IAT scaler/multiplier that can adjust for this (not just in OLSD like we have in one of the COS's), it will continue to be a problem where commanded AFR will not equal reported AFR. The commanded open loop fueling table is where I would adjust the tune to make the car do what you want if you're not using the O2 sensors. Just know that commanded won't equal actual as it comes up to temp.

GM was probably betting on the O2's to handle the minor variations that exist in the stock setup (due to heat soak, environmental variation, etc.). I wouldn't be surprised if that was that table's "purpose" when it was created - a multiplier to alter AFR based on ECT and MAP to hold the car in check until closed-loop fueling kicks in. I would be shocked if these cars left the factory with a calibration that generated actual AFR's equal to commanded in all conditions. It's only been recent where cars (like my Cobalt SS) have come with WBO2's, which make commanded vs. actual a near non-existant problem...

[maudyZ28]

thanks guys,

5.7ute - the heat soak issue is only when coming to start the car after it has been sat after running, it starts to be really lean upto 16:1 but then if i drive off and press the throttle a little it comes back into check when the IAT drops (usually really low have SLP lid and CAI on my camaro). On cruise between 1500-4000 rpm the AFR is exactly as commanded with 14.6 and WB showing 14.6 -14.7 at light loads so the VE is dialed in nicely there.

sspdemon - I was maybe thinking the same think, that O2 sort out idle AFR in closed loop, although they do swing from 15.4 to 14.3 (ie about 14.63) but with low frequency as the gas flow in exhuast is slow and O2's dont fluctuate as fast, so switch from rich / lean slower. I'm wondering however if the AFR on start up is working correct or if this has turned off and just runs from the open loop fueling table rpm vs map. I might just richen these up at low temps such that its not running in the 14.5-15.0 range on cold starts !

[SSpdDmon]

If you take a look at your O2 tables, you can see what's happening. Typically, there's either a timer or ECT threshold that allows the car to transition into closed loop. At start up, the car is in open loop. I think that's the right move (adjusting commanded fuel in open loop). But, don't go too crazy. 14:1 should be good enough. Besides, you shouldn't be too hard on the car until it warms up, which is when it should be in closed loop anyway. :)

[maudyZ28]

yeah I never 'get on it' until it's fully warm anyway. Just interesting how it used to run super rich on start up before tune, obviously VE etc were out from factory. I'll have a check back over my tune and just check VE on idle not in gear and in gear, and up fuelling if required

thanks

[Aloicious]

sorry its been a while, I looked over your log and didnt see much, the only thing I noticed is that you've got alot of IAT temp variation that happens rather quickly. when you're running its down around 13*c, but when you let off the gas and come to a stop it comes straight up to around 35-40*c rather quickly. I would think that heatsoak may be an issue with what you're seeing.