Keith, Chris, Ken!?!?! Someone please help..

[txhorns281]

I don't know if you've been following but i can't get this one stamped out...

http://www.ls1tech.com/forums/showpo...p;postcount=66

So far there have been many ideas but none really seem to fix the problem effectively... (Timing, DFCO, Closed Loop Proportional) You guys have to have some experience with this occurence... Can you help a guy out? I'm all out of ideas and my VE when commanding 14.628 just plain sucks at idle, low TPS, low rpm, and decel... Wasnt like this when commanding 13.0

Full thread - http://www.ls1tech.com/forums/showthread.php?t=256989

Starts out with MAF calibrations but turns into VE inconsistency discussion

[txhorns281]

nothing?

[rattle]

I suspect you might have to move your o2 sensor rich/lean switch point. with headers your exhaust runs a bit cooler at lower air flow settings, cooler translates into sensing richer so you have to tell your computer that your o2s are reading a bit differently now. You will find that adjustment under FUEL, OPEN/CLOSED LOOP, o2 rich/lean VS airflow, dont move any more than 75 to 100mv

[txhorns281]

I suspect you might have to move your o2 sensor rich/lean switch point. with headers your exhaust runs a bit cooler at lower air flow settings, cooler translates into sensing richer so you have to tell your computer that your o2s are reading a bit differently now. You will find that adjustment under FUEL, OPEN/CLOSED LOOP, o2 rich/lean VS airflow, dont move any more than 75 to 100mv

Thank you very much for your input, "Another User" being the exception, I feel like I've been alone on this for awhile now... Either no one has seen the thing that i've been fervently describing, or no one cares, or people know but are being all hush-hush about it... Kinda sucks when you're looking for help so thank you...

so in my case, since i only get these overly negative trims (rich) at low rpm/decel/low TPS, do I want to figure out a sort of rough range of airflow modes I am in during this type of trimming and raise the rich/lean point in the O2 table??? Will I want to raise this point because the computer will consider the excess MV it is reading as less variant? How exactly does the MV swing work??? I know that it is a bit cooler for the O2s downstream on LT Headers so does that mean the O2s report less mv or more??? I am a little confused on which way to adjust my swing points...

I am trying to rationalize this, i know that on either side of the selected MV point it will register rich or lean at that particular airflow mode. so right now the MV that the 02s are reading are on the right side (greater than) of the switch point right??? I'd appreciate any explanation you can offer!

[luv2spd]

I'm sure there are many like me that would love to help figure ths out but our cars are put away for the winter. Anyways I think the only question I can help answer is that with the 02s being further downstream they would register a higher mV just like running richer would.

[txhorns281]

I'm sure there are many like me that would love to help figure ths out but our cars are put away for the winter. Anyways I think the only question I can help answer is that with the 02s being further downstream they would register a higher mV just like running richer would.

thanks guy, you know I've been sick the last few days but didn't even think about this... I'm not sure how much it's related to o2s since even when running in open loop it still does this "rich" thing around idle/low rpm/low TPS/decel

I will try the o2 switch point though in closed loop and see if it helps any... I just don't get it at all.. when i command 13.0 i get 13.0 everywhere.. no problems. When i command stoich, I get it for most places, but the areas I keep mentioning run like they're pig rich or something... and my VE is very smooth and the car still drives almost like stock again.. Just stanks at idle and acts very rich at the above mentioned conditions.... I doubt it's just something with my car or my tune since i know of at leat 2 other people that are having similar problems... one guy is rich like me while another guy is having lean problems...

[txhorns281]

sooooo none of the HP Tuners cast has experienced this problem? ???

[txhorns281]

again...

[frcefed98]

Wish I could help, TTT for you :-/

[BQuicksilver]

...and can someone please explain "airflow mode"? I have no idea what the x axis is and as such cannot mess with these settings. I have headers and suspect that I may have a similar issue.

[MNR-0]

Wait up there fella.

We are here to help. But we have other responsibilities too. Please don't get frustrated when you don't get an immediate response. This is not a self serving forum here. Have you tried a search for Airflow Mode?

Read my explanation on Airflow Modes and Closed Loop Fuelling in these 3 links:

http://www.ls1tech.com/forums/showpo...p;postcount=53
http://www.ls1tech.com/forums/showpo...p;postcount=65


I extracted a simple explanation on Airflow Mode from one of the threads above:

=======
Airflow mode is simply a lookup number for the Base Airflow Mode table. The Base Ariflow Mode table is scaled in g/sec and maps to calculated or derived ariflow, eg. a MAF. So, for example, you could see Airflow Mode 16 for g/sec 40+.

Airflow mode allows us to maintain AFR at part throttle conditions by mapping the O2 mv readings to an Airflow Mode using the O2 Sensor R/L vs Ariflow table. So, we now have a way of correlating AFR to intake charge by indirectly mapping O2 sensor mv to MAF or VE g/s.

[BQuicksilver]

Thanks, I think :

MNR, I've been here as long as you and read the thread on this forum. Nowhere did I complain that nobody was answering my question. Cut the attitude. Hopefully I won't need to say this to you again.

[WS6snake-eater]

POSTED BY MNR

"Ive read this thread and understand the issues and mathematical principles you are talking about. But I will offer a pragmatic view and suggest you are all overlooking an important factor when fuel trimming.

Firstly, GM would have already gone through this mathematical mumbo jumbo to accurately flow rate these MAF meters. The important thing is you get a MAF with a known calibration. You can bet that whever you think it needs to be it will only be out by a few %. So leave it stock until you have determined by how much it is out.

Understand how closed loop fuelling works before thinking that the VE or MAF table is out.

Before anything you need to ensure your O2 sensors are swinging nicely at idle and in motion. If not, alter their gain by modifying the Base O2 Sensor Airflow Mode until it does.

The move into the Base Airflow Mode. The VCM only has a resolution of to 9 cells for O2 switching. You can this by opening the O2 Closed Loop Proportional base vs Airflow Mode table. The Airflow Mode maps to a g/sec Mass Ariflow via the Base Airlfow Mode table. What you want is even and highest resolution for closed loop fuelling up to Airflow Mode 16 spread over each of the 9 cells.

You need to alter your Base Ariflow Mode to suit your CAI plumbing to achieve this. I have 3 Airflow Modes fuelling LTFT cells just off idle and to 12 g/sec. The I spread the remainder Airflow Mode Cells so that there is resolution of 2 cells per Fuel Cell. This will result in rock steady fuelling in closed loop.

My LTFTs are within +/-1 at all times. My STFT cells are mostly 0 and are rock steady under ALL driving conditions.

Having nailed your fuelling cells and calibrated the closed loop switching Airflow Modes for max. resolution for each Fuel Cell you can modify your MAF table by the total average % of LTFT as shown in the LTFT histogram in HPTuners. Mine was showing up to 2% so I scaled it up by 2% to result in consistent 0 and +/-1 LTFTs across the board.

If I was performing a SD tune I would then calibrate my VE table so that it is inline with my derived Dynamic Air calcs. I am taking the approach here that the MAF is the correct and the VE table is out - not the other way around. Since my logged Dynamic Air calculated off the VE table was already inline with my MAF g/sec I didnt need to and just smoothed it out a bit.

I now have excellent throttle response and fantastic fuel economy. Closed Loop fuelling is rock sold steady and won't change cell by cell - a common frustration when fuel trimming. It will change as the ambient temps. vary but by no more 1% per 10*C. So if you get it set at LTFT 0 for 15*C you can be sure you have good fuelling from -5*C to 35*C - pretty much all driving conditions.

This is the approach I took and it has worked tremendously well. It is a new approach to fuel trimming and so would appreciate your feedback on your successes/failures.

I am inclined at this point to believe the Base Airflow Mode table is the key to closed loop fuelling rather than the MAF. Base Airlfow executes closed loop fuelling - not the MAF. The MAF merely provides g/sec measures to tell it what to do. Kind of like a car needs a driver."


To me a lot of this sounds very reasonable. I am still very interested in seeing a screen shot of your gain values, switchpoints and base o2 tables. I think that it would go a long way in helping us understand your methods, if we had a visual to look at.

Matt

[jimmyblue]

The low flow (low RPM, low MAP) has a lot of SD and a little
MAF in a combined airflow calculation. The proportioning
"fades" to all-MAF at 4000RPM. At idle I've seen almost 1:1
response to adjusting the VE table (if you adjust the cells
on both sides of your idle RPM and idle MAP).

Look at your FTC boundaries. Do you have your first RPM
point at 2500 and the second at 6502? That's unhelpful.
One cell to cover idle through cruise, trying to cover a
very changeable VE and MAF-blend as well? What you
really want is to find the extents of your closed loop
driving space (RPM, MAP) and subdivide it using the 16
cells. Don't worry about 15 being all WOT, that's fine.
But use them all and each one will fit better and be more
informative. With them sliced finer, the lowest-RPM one
will be more entirely VE-driven (simplifying the tuning
effort in my experience).

I think anyone with headers should not even try to tune
LTFTs until they replace their front O2 sensors with the
'vette rears. Stock F-body sensors do not stay lit with
their lower wattage heaters. This corrupts the feedback
and the trims at idle / low cruise. Don't waste your time
fighting a sensor problem; replace. You -might- make things
better by massaging the airflow mode and the switchpoints
and the time constant params but if they're dead cold then
250mV switchpoint is as good as 350mV, i.e. not. If you
have seen a heater code or seen the car drop out of closed
loop and stay open-loop until you shut down, that's your
sign that you're being bit by this. If you're marginal than you
will see the idle LTFT drift back and forth and never stay put,
across a driving session as the exhaust heat changes.

[WS6snake-eater]

I have already changed to the vette rear o2's and it definately helped a lot. I would surely recommend it to anyone doing longtubes. The hell with o2 extensions. I also have already lined out the LTFT boundries, to allow for better resolution and control. One day my LTFT's at idle are fine other days they are all over the place. In general I think this is due to weather conditions. Today there is water on the road...water touches the headers, the headers are then cooled and we are back to fugged o2 readings. I too do not think that you should change the switchpoints and such to correct a mechanical issue. However, if the other areas have been addressed ie. new sensors, LTFT boundries, and even header wrap, then we must move on to the next relevent command in the chain and that would be the tuning. I believe that MNR is on to something with the gain and error tables. For instance it seems like lately we have seen a lot of folks turing off their idle proportional tables to help with idle conditions (surging), and it seems to be having some success. So what is the difference between the the idle proportional and regualr tables? Well it is their gain and error configurations. This alone tells me that something is there, I just haven't quite grasped the concept of it yet. Apparently MNR has, and that is why I would like to take a peek at his setup. Perhaps he can post a bin for our viewing.

[WS6snake-eater]

The low flow (low RPM, low MAP) has a lot of SD and a little
MAF in a combined airflow calculation. The proportioning
"fades" to all-MAF at 4000RPM. At idle I've seen almost 1:1
response to adjusting the VE table (if you adjust the cells
on both sides of your idle RPM and idle MAP).

Jimmy on another note, I beleive that ver 1.6 was supposed to allow for blending MAF vs VE, to be controlled by the tuner. I know it lies somewhere in the depths of the dynamic air tab but I haven't been able to put my finger on it yet...Have you had a chance to play with any of the new dynamic air settings? Ideally I would like to be pure VE below 1200 rpm then gradually add a linear MAF function as the RPM rises until 4000 RPM where full MAF would take over. I think it will envolve re-aligning the zone boundries, and the VE correction factor. I'm not sure how I could make it a linear gradual increase to the MAF only. For instance I would like it to use only40% MAF input at 2000RPM, then at 3000RPM be using 75% MAF blending at 4000 100%

Do you have any insights on how to make this possible. I have read the help file for that particular section over and over, but I just don't seem to grasp it. Hell I'm not even too sure how one would verify if it is indeed blending bewtween MAF and VE.

[MNR-0]

Thanks, I think :

MNR, I've been here as long as you and read the thread on this forum. Nowhere did I complain that nobody was answering my question. Cut the attitude. Hopefully I won't need to say this to you again.

After re-reading my response it sounds like it is aimed at you when this was not my intentions. I was directing that part of my response to txhorns281 as he was getting frustrated at the lack of repsonse. I was typing one thing and thinking of another. No offence intended.

[MNR-0]

I am still very interested in seeing a screen shot of your gain values, switchpoints and base o2 tables. I think that it would go a long way in helping us understand your methods, if we had a visual to look at.

Matt

Screen shots of Gain values and Base O2 settings are posted in LS1Tech here --> http://www.ls1tech.com/forums/showpo...p;postcount=74

The switchpoints are stock - as my bin is already available on the horist bin repository you can download them from there. That bin does not have the new Airflow Tables though.

That bin also has just a tad too much timing at WOT for an uncracked LS1. In my current tune I pulled timing back a points post max. TQ.

[S2002S]

Regarding the use of rear vette O2 sensors for cars with LTs. I changed out the passenger side only and did some logging. I didn't see any real change in the switching behavior between the drivers and passengers O2 sensors. I'm using ceramic coated headers, by the way....

Comments?