Installed longtubes, now STFT/LTFT at idle are pulling fuel out

[elementaltoad]

I have a 5.3 LM7 with a SLP 234/228 cam, LS1 intake, and longtube headers. Previously the car had manifolds which I knew would hold it back. It was tuned with the manifolds on it, and after installing the headers and logging the tune I'm not sure where to start dialing it back in.

From a cold start without touching the gas, as soon as the O2 sensors start reading, the STFT start pulling fuel and adding to the negative LTFT until they get to around -18%. Each time the STFT hits the most negative point, it will reset to 0 causing a bit of idle surge, before going negative, then resetting back to 0, it continues to loop doing that over and over. I'm a bit of a novice, but I'd like to learn how to take care of tuning myself, I would log trims and pull the difference from the VE table to get it back in line, but I have a hard time believing that putting headers on it would require me to pull rather than add.

I would appreciate any advice and insight into what might be causing this and where to go next, this is the first cammed vehicle I've tuned.

WhitebirdWIP.hpt
whitbird LTs.hpl
LS1.Layout.xml

[dermotw]

Longtube headers and a cam with overlap often = your o2's becoming inaccurate at idle, unfortunately. Looks like at idle your o2's are not really cycling at all, and assuming you have a fairly standard tune, no OL, they should be, even at idle. Again, thats a consequence of cam/headers really... heres a snapshot of mine, with similar cam/headers, idling, not a very good example (car wasn't set up) but you can see that the o2's cycle high/low every few seconds...compare to yours (the scale is same, one min).
Capture.JPG

BTW can't open yr .hpt file... probably its locked?

[Hutchinson]

Elementaltoad, I have the HT383e with long tube headers - cam specs Lift .431in .451ex / Duration 196in 206ex. I placed the O2 sensor bungs in the collectors themselves,.. instead of downstream, to assure I wouldn't throw my O2's off incase the collector flange loosened/developed a small air leak.

I've attached a copy of a scan I did couple weeks ago, sitting in my driveway, watching S/LTFT. You'll see my O2's switching and my STFT's adjusting my LTFT's at idle,....im simply wondering why my LTFT's go negative 10/8 or so at idle, but,.. once I blip the throttle, they jump right back up to 0's. But, if I hold my rpm at around 1500 rpm they'll eventually creep right back down to the same negative 10/8 roughly.
Hope the scan helps you a little,.. maybe check your O2's or an exhaust leak before the O2's,....I'm not a tuner bro, and a newb to boot,... just trying to help.19MAY17 Driveway engine scan after 5.1 tune install.hpl

[elementaltoad]

Longtube headers and a cam with overlap often = your o2's becoming inaccurate at idle, unfortunately. Looks like at idle your o2's are not really cycling at all, and assuming you have a fairly standard tune, no OL, they should be, even at idle. Again, thats a consequence of cam/headers really... heres a snapshot of mine, with similar cam/headers, idling, not a very good example (car wasn't set up) but you can see that the o2's cycle high/low every few seconds...compare to yours (the scale is same, one min).
Capture.JPG

BTW can't open yr .hpt file... probably its locked?

Try this one I attached, I've noticed with the new version I can't modify any OS properties. This one might be unlocked.

That's what is bothering me, I read a bit about modfying O2 switch points and I'm wondering if I may need to look at doing that. They move extremely slow at idle, probably the cause of it pulling fuel. The car had a professional tune done previously and the only change I've made is adding the longtubes and 4" exhaust, so I am hesitant to mess with too much of the tune's base. VE, PE, spark, RAF, etc have all been set by them.

WhitebirdWIP.hpt

[elementaltoad]

When you blip the throttle the trim cell changes to one that's probably not being hit frequently if at all. When you are holding high idle at 1500rpm and the cell trims again to roughly what normal idle trim is, it sounds like the tune is about 10% rich over what it wants all the way around, which isn't abnormal if it's a canned tune. Most of the LS1 stock F-Bodies I've logged all seem to be about 10% over or under.

[elementaltoad]

Ok, I cobbled together an entirely new tune file. For some reason the original I posted was not behaving. I went through page by page and made sure everything was changed over to 5.7 data, it's a 5.3 but that is the closest file I have that I trust. I also changed the MAF data to a MAF chart that I tuned for my Z28, which is pretty close to dead on for that car. It looks like it's about 5% off for the cammed 5.3. I also changed the stoich back to 14.6 from 14.3 because none of the other tables looked to have been touched including the EQ ratio, so I am not sure why the tuner dropped it to 14.3, but it doesn't smell as bad at idle anymore, and it's not pulling as much fuel out. It's only going about 10% negative on one bank....part of that might be due to this motor having a new rod and piston put in after it burnt a ringland when it was boosted. I'm betting it eats a little oil.

Here is the new tune file that is unlocked. And a RussK idle scan, as well as the generic scan I did with LS1 parameters.

If someone could take a look over the tune, and say looks good, that's all I need, I just expected a lot more from the tuner that tuned this car and I'm worried I might be missing something.

[dermotw]

That timing table needs fixing, it's pretty basic/hacked . The VE not so bad. If you want the o2's to work as they should you will likely have to change quite a few settings, in fact you should have a look at how they work away from idle, its possible that even then they aren't behaving. If they aren't and you are in CL, then you can never really get it to behave properly, although as it is it seems surprisingly good (considering the o2 correction is basically not functioning at idle)

[elementaltoad]

That timing table needs fixing, it's pretty basic/hacked . The VE not so bad. If you want the o2's to work as they should you will likely have to change quite a few settings, in fact you should have a look at how they work away from idle, its possible that even then they aren't behaving. If they aren't and you are in CL, then you can never really get it to behave properly, although as it is it seems surprisingly good (considering the o2 correction is basically not functioning at idle)

Thanks for taking a look! When I was going back through to cobble the tune together last night, I smoothed out the main spark and idle/gear spark tables and made them a bit less..."Canned". VE looks a little low really, but it fits similar trends I've seen in other cam tunes so I left it alone for now.It does seem to run surprisingly well as far as what data the scanner is giving me, which really made me worry since the O2 aren't reading at all, and so many of the tables were left stock or just hacked together to work. After messing with the tune some more and running it again yesterday, they do seem to come alive if I hold the throttle at 1500RPM or more, so hopefully I can solve the idle lazyness along the way or I'll force OL once everything is as dialed in as I can get.

[dermotw]

This is the basic rule as I understand it (not written by me, but I forgot the original author);

"If your maintaining O2 switch rate and running longtubes with no or gutted cats, then move your precat O2 downstream further into a solid diameter pipe and then multiply proportional airflow by something like .835 to .9ish and multiply integrator delay by 1.25ish or higher."

These are the tables we are generally talking about for this, note there are different tables for idle, don't take any notice of the numbers in the pic;

Capture.JPG

[elementaltoad]

This is the basic rule as I understand it (not written by me, but I forgot the original author);

"If your maintaining O2 switch rate and running longtubes with no or gutted cats, then move your precat O2 downstream further into a solid diameter pipe and then multiply proportional airflow by something like .835 to .9ish and multiply integrator delay by 1.25ish or higher."

These are the tables we are generally talking about for this, note there are different tables for idle, don't take any notice of the numbers in the pic;

Capture.JPG

That's what I am tinkering with now. I went ahead and replaced everything in the tune file with 5.3 stock tables first so I know what baseline I'm working with. The only thing not from the 5.3 data is the injector data, since I have a LS1 intake and LS1 injectors. I also read the thread that was here: https://www.hptuners.com/forum/showt...l=1#post381282 which seems to mention what you are saying about modifying the values for O2 Airflow and Integrator delay.

What I didn't understand is there is some talk about "Moving the O2 sensor" and that will dictate how the values are changed, but I couldn't parse if the values needed to be increased or decreased in a lazy/longtube situation since it looked like some of the guys were having issues with very erratic and quick O2 readings. I guess I'm just not understanding the relation of the tables and what they actually do.

It sounds like the two in the middle, base vs airflow and base vs airflow mode need to be reduced by that .83-.9 value, and this represents the actual fueling change the O2 sensor would be seeing to make a change? Integrator Delay vs airflow mode seems to be increased to slow down or smooth out the switching if they are too fast, so I don't know that I need to do that at the moment. The proportional gain vs O2 error seems to be a multiplier that will affect the change in fueling to get the swing going the other way, rich to lean, or lean to rich. I just don't know how to modify them right now because mine simply seem to be lazy and not getting much of any read. If I could get them reading I think I could figure out where to go from there.


Here are the tables as they appear in my tune.
WhitebirdO2.JPG

[dermotw]

Well here are my settings, but my car is quite modified...;

Capture.JPG

What you have to do (probably) is set it to add enough fuel when it goes lean (or remove when rich) to 'kick' the o2's the other way, thats the basic idea. right now your logs seemed to be saying that you were not giving them enough of a kick...

The integrator is slowed down so that it gets a chance to see the changes, because they WILL be slower in a cammed car (imho anyway) never quicker, even at higher speeds than idle they may be slower.

Their reaction is slower at idle because there's just less gas going past, and perhaps not such a steady flow either, and with a cam, the a/f can be screwed up, you may get some raw fuel and that confuses the o2's as well. If your particular cam does not have overlap you will be much better off (easier to setup). Mine has about 10 degrees overlap.

If you really can't get it to work, then moving the sensor is another option... getting a bit desperate by that point 'tho! I did not move mine, they are at the standard points in my hooker headers (no cats at all, no rear o2's). BTW bigger diameter header/collector pipes would also make it harder for the o2s.

If you take logs of how it switches when cruising (hopefully quite well) then you can compare, but usually it will never switch so well down at idle, and not unusual to take several seconds for the o2s to stabilise and start switching again when you come to a stop, for example...

[elementaltoad]

I'll give my tables some adjustment and see how it does. I see yours are modified by about the same values as the other thread stated, I'll keep increasing the O2 Integrator delay until I get some solid readings. I appreciate your responsiveness, I think part of my problem is how butchered my tune was with it being originally a 1997 ECU, then imported into a 0411 truck ECU, and still having LS1 values. With all of the 5.3 values now hopefully things will line up a bit better and make it easier to get switching back so I can fine tune it.

[elementaltoad]

No such luck with the O2 changes. I got the driver's side to read a decent bit, but it is still weak. I'm going to replace the O2s and try again. Here is the tune and log from today.

[01ssreda4]

The tuner put in 14.3 to compensate for the 10% of ethanol you find at most gas stations now. Also, trims arent necessarily telling you what you need to know. A wideband will. Get one.

[elementaltoad]

The tuner put in 14.3 to compensate for the 10% of ethanol you find at most gas stations now. Also, trims arent necessarily telling you what you need to know. A wideband will. Get one.

Wideband and new NB O2s will be next for sure. Shoestring budget at the moment. Isn't just changing the stoich to 14.3 without modifying anything else a bit careless? It certainly smells god aweful rich, VE and spark were the only tables touched. I set it back to 14.6 and it doesn't burn your eyes nearly as bad, LTFT/STFT are also much better, but that may just be from finally getting the NBs to read a bit better.