O2 settings...??? WHY

[91chevZ71]

Ok, so I've been dealing with an oscillating AFR issue at low RPM (13.0-17.0) :eek:
mind you, this is all in closed loop. In open loop, no issues.

Also, my AFR's would seem to hang around 15.0-15.5. I finally did the smart thing and datalogged for a while.
I put in a new NB O2 (AFS 74) and also I'm running a ZT-2 Wideband O2. OK, so this AFR thing only happens in closed loop, and I first looked at the PRP settings. I thought that the computer was overcorrecting based on PRP gains that needed to be adjusted. well, I figured that since I have 105 lbs of fuel now and stock is 61 lbs, I'd reduce the PRP tables by about 40%. No change...still had the oscillating AFRs.
I then moved on to the BLM update rate, slowed it down a bit, sped it up, no change. Still crazy AFR swings.
I then drove in open loop while monitoring the NB's voltages when I was at 14.7 according to the wideband. This is where it gets weird.
Now, we know that around .450 v or 450 mv is the NB's 14.7, right? Right. When I looked at my NB's voltage when WB said 14.7, the NB was at 850 mv. Yah. That confused me too. I changed my O2 settings to have 850 mv as the mean R/L point, with 800 being lean and 900 being rich. This has completely solved the problem. I'm asking myself why, but around 850 mv the engine runs awesome and WB confirms good AFR. I don't know why I needed to raise the INTegrator's O2 settings so much, but I did.
So, it turns out that PRP gains were not at fault, as I had originally suspected, but the millivolt settings needed to be raised CONSIDERABLY. Maybe there is something with this particular O2 sensor, or maybe it's just a combination of this engine, these injectors, who knows what else. I'm sure everybody else's NB 02 runs great at 450 mv as 14.7, but mine likes 850mv.

I'm not really sure what I'm trying to say with this stuff, I think I'm just glad it's solved. The guys at thirdgen helped out a ton, as well as some guys on here.

[93V8S10]

Glad to hear you got yours worked out. Looks like we had the same problem, just not to the same degree.:burn:

[oldred95]

Oh yea the 02 voltage tables will do weird things. With the stock tables and correcting the VE's to 128 mine was running so pig rich it was insane. On cold startup it just dumped fuel in open loop and in closed loop it was able to correct itself enough to at least idle. Ended up being the 02 settings way off. Something about headers, the 02 sensor only being on one bank, and it being a little further back then original plays with the sensor reading.

[91chevZ71]

so did you end up raising or lowering your millivolts, oldred?

[oldred95]

so did you end up raising or lowering your millivolts, oldred?
Raised. Chris (fast305) had ran a simular exhaust setup and 02 placement and found a set of values that worked well. I tried them and sure enough my VE's instantly became pig rich. Seems to be working ok. They may not be the ideal settings but far better then the stock settings.

[91chevZ71]

dude, this thing amazes me. how can the voltages vary so much? seriously? I am amazed I didn't burn valves.

-edit
I think a lot of this came from my belief/misunderstanding that 450 mv was 14.7 for all setups, end of story. turns out that isn't true

[oldred95]

dude, this thing amazes me. how can the voltages vary so much? seriously? I am amazed I didn't burn valves.

-edit
I think a lot of this came from my belief/misunderstanding that 450 mv was 14.7 for all setups, end of story. turns out that isn't true
How would it have burnt valves? Lean conditions? I really don't see why it was causing the lean swings, unless the PCM was trying to correct that much and swinging it way lean to do it. The reason why it was fine in open loop is because the open loop table values are just commanded, they aren't necessarily actual AFR values from what I understand.

Hows yours running now? Past 1500 rpms mine is a blast now. I've tweaked the timing a hair more and will try it tomorrow and see if it fixes the flat spot I'm having from idle to 1500. My mileage has gone up from 12 to 13 mpg. The tank with 12 was me babying it all around town. This last tank that was 13 was a few short highway runs, mostly town driving and about 10 WOT runs. Not terribly bad I didn't think.

[91chevZ71]

mine is running pretty well right now. AE needs help, but that's not a big deal. It pulls pretty da*n hard through the gears, and the best thing is that the AFR's hang at 14.0-14.3 in closed loop through high MAP, high RPM pulls--not in PE. PE behaves normal, 12.5 commanded and 12.5 measured.
It feels like a different truck. I am somewhat embarassed to say it, but I had the O2 settings wrong from day 1 for closed loop and totally overlooked them!!! It actually reminds me of my 95 Z I used to have. Once I get AE dialed without battling this AFR swing issue it should get real interesting.

For now, I'm throwing the mileage priority out the window

[oldred95]

mine is running pretty well right now. AE needs help, but that's not a big deal. It pulls pretty da*n hard through the gears, and the best thing is that the AFR's hang at 14.0-14.3 in closed loop through high MAP, high RPM pulls--not in PE. PE behaves normal, 12.5 commanded and 12.5 measured.
It feels like a different truck. I am somewhat embarassed to say it, but I had the O2 settings wrong from day 1 for closed loop and totally overlooked them!!! It actually reminds me of my 95 Z I used to have. Once I get AE dialed without battling this AFR swing issue it should get real interesting.

For now, I'm throwing the mileage priority out the window
Have you seen my timing curve? Its pretty rediculous but it is responding very well to it. Also learned my AE settings were rediculous. Now me AE MAP is just a very slight gradual gain from 0 to 80 KPA and my AE TPS is now under 3000 usec and I've still got a little bit of a rich condition on WOT take off. Its fine up until half throttle and then it goes rich.

[91chevZ71]

I have seen your curve. I keep telling myself give the engine what it wants, even if it seems ridiculous (to a point)


can't be scared to stray from stock settings. I had this thing pounded into my head about NB O2's and 14.7 always being 450 mv

[oldred95]

I have seen your curve. I keep telling myself give the engine what it wants, even if it seems ridiculous (to a point)


can't be scared to stray from stock settings. I had this thing pounded into my head about NB O2's and 14.7 always being 450 mv
I'm trying to get the lowest pulse width possible without spark knock, and keep a low TPS %. I'm down to 16.4% throttle on flat level highway at 65 mph and a pulse width bouncing around 1.9 to 2.1 or so. MAP is around 55 KPA and 35-36 degrees advance.


You really can't. Stock might have worked fine when it was stock but when you go and change things it doesn't usually work right at all.

[91chevZ71]

those look like pretty good numbers. what's your MPG on highway with these settings?

[oldred95]

those look like pretty good numbers. what's your MPG on highway with these settings?
Not sure yet but it should be pretty good. Going by the VE's its taking roughly 15% more fuel to do 65-70 mph down the highway then idling at 650 rpm in park so really almost no fuel consumption going on. Again all closed loop. I would hope it will get 17ish now. I'm running 15w 50 mystic engine oil now and I'm going to switch to 5W 40 the next oil change and also put some lighter weight synthetic gear lube in the rearend soon. FWIW the other day I noticed road surface also makes a difference. I went from pavement with gravel packed into the surface of it to just pavement, both smooth and flat and it dropped my MAP by about 2-3 KPA. Not much of a difference but it was there.

[Blue71]

we know that around .450 v or 450 mv is the NB's 14.7, right? Right. When I looked at my NB's voltage when WB said 14.7, the NB was at 850 mv. Yah. That confused me too. I changed my O2 settings to have 850 mv as the mean R/L point, with 800 being lean and 900 being rich. This has completely solved the problem. I'm asking myself why, but around 850 mv the engine runs awesome and WB confirms good AFR. I don't know why I needed to raise the INTegrator's O2 settings so much, but I did.

Interesting, so basicly you match the NB mv setting to the WideBands 14.7


ZT-2 Wideband O2, couldn't find much info, Do you need to calibrate it like the LC-1 in open air ?

where is the narrow band location in the exhaust, do you have two bungs one for NB one for WB side by side in same location?

[91chevZ71]

Zeitronix ZT-2
http://www.zeitronix.com/Products/zt2/zt2.htm


no calibration. not sure if this is a good or bad thing, but from my experience the ZT-2 works great.
Yah, I have the AFS-74 3 wire O2 in the driver's side header, bung is on #5 primary, about two feet from the chamber. The wideband is on bank #2, about 3 feet from the collector. I think somewhere in the instructions it says to keep it further downstream so it doesn't cook. about 2 feet in front of the cat. Also mounted the sensor in the 10 o'clock position on the pipe, to avoid moisture saturation. That's in the instructions also. So, have the NB on bank 1 and the WB on bank 2. replaced the plugs today, all showed lean.
Yah, I basically tuned the NB to the WB, but based on engine response and closed loop operation with AFR's hanging around 14.3 it was the right thing to do

[Blue71]

Yah, that's what a thought you had but wasn't sure, I had looked at that link
but didn't see any thing about calibrating the sensor, maybe with the ZT-2 you don't
need to.

My setup is little different, mandrel bent cross over into a Flowmaster Y collector,
put the NB at 2 o'clock and the WB at 10 o'clock in the Y collector.

The NB and WB seem to be reading real close, But I do get a lot of fluctuation on both
in closed loop, openloop no problems.

Maybe I'll try the NB in the #5 runner and see what happens.

[91chevZ71]

where is your NB right now?

[Blue71]

where is your NB right now?

Last time I look it was still on the truckj/k


Wb 14.7, NB 460mv that's in openloop
hard to tell in closedloop move a round to much between 14.2 to 15

[91chevZ71]

*asian accent*
ha ha ha
you so funny round-eye
make A #1 joke

lol

[Blue71]

See Post #16

Headers to: http://thunderracing.com/catalog/?action=mshop&mid=131&sid=438

Foot and a half back on the passenger side, after the header.

[91chevZ71]

yah, I saw it. I think I'm gonna run a Y pipe and convert from the duals
need more tq

don't get me wrong, it pulls, I just think there's more to be had with the Y. plus I spend all day from 600-2500 RPM

[Blue71]

I have been happy with mine, have all kinds of tq down low + HP on top.

2.5 to 3inch y to a flowmaster 50 Series SUV 3 inch in 2-2.5 out exiting behind the rear wheels.

[getsideways]

I changed my O2 settings to have 850 mv as the mean R/L point, with 800 being lean and 900 being rich. This has completely solved the problem.

did you change these values at all the airflow's in the o2 tables or just the low airflow values in the o2 tables?

[91chevZ71]

the whole thing. I've been adjusting it a lot, but Mean R/L seems to be around 820-830 mv for about 14.3-5

[91chevZ71]

O2 window has alot to do with things, FWIW. about 4 1/2 times the INT's delta mv change. IOW

1 part O2 Error for INT Correction
4.5 parts O2 Window for Fast R/L

I've tried having the window real small, resulted in psychotic INT behavior.

If the windows is too big, the INT won't adjust, basically running open loop.

sped up INT update rate about 1/3. helps too. running great FOR NOW...lol

I still don't know why the narrow band needs to set so high in terms of mv values, but whatever. engine performance doesn't lie. damn thing runs at about 14.5 all the time, except at idle (open loop). my idle takes a huge crap when it runs any leaner than 13.5