I've been chasing a problem for a minute now, that I think I can finally attribute to my headers.
Car smells rich as it warms up. I did some idle tuning today to check my tables, and you can see in near the end of the attached log...as the engine warms up, and the airflow drops to maintain idle, the 02 sensors become so lazy they start reading lean. my plugs and nose say otherwise. This is an at idle only problem, once you blip the throttle it is good to go.
I do have a little bit of an issue with a lean restart in the lower end of the table which corrects itself within a couple of minutes of driving. I am attributing this to WB heatsoak as I stop to upload changes to the PCM and have been trying to tune around this on my C5. My Silverado, naturally, does not have this kind of problem.
WB is installed in front of my cats.
Seems to tune OK otherwise. Idle is quite the challenge with longtubes though. Problem exists in MAF and SD modes, open or closed loop. WB picks it up too, but the PCM is still commanding 1.00 lambda.
Seeing that my C5 is a gen 3, and I drive it (all over), I'd rather not just ditch the 02's. I'd rather work the problem if I can. So is there any sort of 'band aid' for this? raise the idle RPM a little higher for more airflow over the sensors? adjust the rich/lean voltages on the sensors near idle? I have even contemplated using the AIR ports in the engine compartment and modifying them to be a place to install 02's (though it would be pretty close to the head).
Tonight the 02's just stop switching altogether and flatline once the temps got to about 210, at about .090v.
I did go over everything, checking vacuum lines for leaks, leaks between the MAF and TB, etc...even the 02's are NOS delco, correct for the car, and the WB sensor only has a couple hundred miles on it.
I'm going to attach my file as well, it's still a work in progress but it seems to run pretty decently, but not perfect.
Car is an 02 C5 Z06, LT headers, cats, baby cam, ported heads, intake and induction mods.
I'll give it a shot this afternoon after work and report back. I'll let it get good and hot and pull another log. Thank you.
When I get the chance I'll pull up a compare file and try to understand these changes a little bit better.
Would it help to raise the idle RPM slightly to increase airflow past the sensors as well? I can see maybe bumping it just a tad to like 950 from the 850-875 it's at now. The cam in it is pretty small, so I'm sure having a cam capable of low idle RPM's with all the problems that come with 02's and LT headers is probably what has created this problem.
When O2 position is changed there is also a change in the control delay time. Pulse has to travel a longer distance from the exhaust valve to the O2 sensor due to the LT's. These changes account for it.
Idle of 750 rpm should be more like it. Either way, idle speed shouldn't matter for the O2 problem you're having.
OK so I got a chance to run this and there is definitely an improvement. It isn't so quick to start leaning out, the 02's were switching. I probably let it idle about 20 minutes or so with the hood closed and it seemed to stay spot on.
I went back and touched up my VE (which now showed lean on the bottom end) and pulled probably a 40 minute log which was more than enough.
Again, I had to drive it around for a couple of minutes before starting the log because of what I am assuming is the effects of heatsoak.
When I flashed the corrections and switched back to MAF tuning, I could notice the 02's started getting glitchy again and stop switching. So It's doing the same thing, just not as much or as easily. But I think we are on the right direction, the data was alot more consistent then it has been up to this point.
Is there a way to log this to 'dial it in', or is it just trial and error?
I did notice that when I turn the 02's back on, both before and after, both banks are pulling 8.6% at idle.
What are the conditions when it starts glitching? Idle, cruise, etc?
Log would be nice.
If you want to try some stuff look at the Proportional Airflow Mode table. Lower the values by multiplying the table by .8 then see what happens. Increase values in Integral Delay Airflow Mode by multiplying by 1.2. Do each table individually so you get a feel for how they work. Then mix it up.
Last edited by SiriusC1024; 08-11-2023 at 08:18 AM.
My computer has given me hell in attaching files in the last couple of days for some reason.
I'm fixing to head out to go play with it. Im attaching a couple of logs that I last took that I'm hoping to rectify today regarding the 02's getting lazy.
That calibration is the latest one I'm on, that was with everything reanabled. It's corresponding log still shows an 8+% fuel trim at idle.
Maybe it would help if I 'upgraded' the narrowbands to something that ran hotter to keep them switching?
I notice all these tables refer to closed loop, so does this mean the changes have no effect on how it runs in OLMAF when tuning? They dont switch well OL or CL.
CLMAF - High idle settings made it so that TPS at idle exceeded Proportional Idle Thresholds. It was running up in Mode 8 (cross reference Mode vs Airflow table - 1.95lb/min). If you're still having trouble there look to adjust Idle TPS Thresh.
OLMAF - Looked good.
Adjusted O2 sensor settings for the high idle.
Importantly, why are you idling so high? Suggestions for idle tune attached (many changes).
Last edited by SiriusC1024; 08-13-2023 at 06:30 AM.
I think the idle speed is 800 from the factory. I think.
It does have a cam in it, though it’s pretty small…I haven’t really experimented with lowering it much, when I got the car it was set to 950 (but it chopped hard, idled lean and I had to fix things like holes drilled into the TB)
At 900 the idle tends to smooth out. Under that the car tends to vibrate. I think the motor mounts in it are causing the NVH to get a bit out of hand.
Reply With Quote