VE tables in closed loop

[skala308]

I am confused regarding the use of the VE tables in closed loop. As I understand, in closed loop the O2 sensors will control the fuelling based on the readings of the O2 sensors.
So when running in closed loop with lambda being targeted and not at WOT, is the part throttle VE table used at all?

If the VE table is never used in closed loop, what is the purpose of logging LTFT and STFT for adjusting specifically the part throttle VE table? Is it a waste of effort to log the fuel trims?

I understand that in open loop then the VE tables are used.

Please help me out here.

[skala308]

Nobody have any inputs? Dont be shy, we should help each other here.

[skala308]

I would like some comments on this log scan. Still haven figured out the impact of particularly the part throttle VE table in closed loop.

[pointofview_365]

think of the o2 sensors as a way to monitor the feed forward system. Doesn't matter if you are MAP or MAF. The engine is going to need a way to modify the base air equation depending on variables, like AIT, Baro, Etc. Fuel is your known quantity. It is the air that is unknown. Logging your fuel trims will tell you a lot about the Air pump your driving around demanding Torque from. On my truck, the VE table is always used regardless if I'm in OL or CL because it's a speed density system. Think of it this way, the fuel trims is the control of the feedback system. If anything is incorrect with the feed forward system, the fuel trims will modify the base air equation so that the fuel weight to air weight can be corrected. Doesn't matter, you will always want to modify your VE tables, no matter what system(MASS AIR FLOW Or SPEED DENSITY. If you loose your MAF, the system uses Speed Density(VE) as your backup. If you loose both MAF AND MAP, there's a third referred to as Alpha N that uses the Throttle plates effective area. Under this type of failure, all your monitors would default to this base calculabration of ALPHA N. Not sure if this answers the question, but always modify the VE table using fuel trims just incase of some failure.

[skala308]

Thanks for comment pointofview, as you likely know, the Chrysler/Jeep speed density (SD) or VE table uses the MAP sensor plus Barometric input as a Pressure Ratio.
However, I am convinced that in closed loop, the SD is not big in play.

I just did a run staying in closed loop with a file where the VE table was bumped up with 25%, to see effect on STFT log. As I suspected, no real change, which confirms to me that making changes to the VE table for the Chrysler/Jeep will not influence rich/lean while in closed loop. The initial stoich numbers and O2 sensors will control the fuelling condition, plus the voltage at which going into WOT and thus open loop.

Been chasing my tail with this damn VE table.

[HaasExp]

I just did a run staying in closed loop with a file where the VE table was bumped up with 25%, to see effect on STFT log. As I suspected, no real change, which confirms to me that making changes to the VE table for the Chrysler/Jeep will not influence rich/lean while in closed loop.

If the NN is still enabled on these systems, then the VE table will have little to no impact on the trims.

[skala308]

Hi HaasExp, thanks for comment. No, NN has never been enabled. I have thought about enabling NN, but I dont have a wideband sensor and NN tuning is very complex, or so it seems. NN uses all sensor inputs plus the VE table, in closed and open loop.
Having NN disabled, in closed loop, the O2 sensors plus IAT, ECT, MAP/Baro readings are used. Having digested what pointofview mentioned, I think he is correct in that in closed loop, the O2 sensors need to reference a baseline, in order to know at which PRatio/RPM there is a deviation from stoich. That is possibly how the log scan can then indicate which cell in the VE table (under speed density) is rich/lean.

I will keep logging and with the good results I presently have, will wait for more meaningful LTFT results before adjusting the VE table. That means, I will not reset the adaptives in the scanner, in order to not clear the LTFT historic readings.

Will keep posted, hopefully this can be of use to other new tuners.

[pointofview_365]

No! O2 sensors are just stupid switches... It's the ECM microprocessor that takes the voltage signal and turns it into usable data for the base Air equation. Anything between , let's say .2 to .8 is stoich. That's all it cares about. Anything below .2 is lean and Anything above .8 is Rich.

Here: the best video ever made to understanding advanced fuel trims. You need to understand this to properly tune your ride...

https://youtu.be/oULtX-NiKRE

[skala308]

Many thanks, much appreciated

[K Rob]

following

[skala308]

K Rob see the comments in the post VE Question started by hoover further down. My question was well answered there. Rockystock and 06300CSRT8 explained it very good.

[skala308]

Returned from 2000km trip from coast inland to very warm region. I can say that baro readings, ambient temp and air intake temp has effect on LTFT readings. Engine operating temp also has an effect. This then makes VE table corrections rather tricky.

[rockystock]

The strategy I try to use is to tune in "nominal" conditions i.e., when the other parameters should not be contributing significantly to the baseline. I'll try to get the tune dialed in, in Spring/Summer, and see what the same tune will look like in winter. Any big differences, then see if the VE factor tables can help. If you have mountains nearby, then do your baseline tuning at low elevation / higher temp, then look at the higher elevation / low temp logs.

If you look under your Speed Density tab, you'll see several multipliers for VE to compensate for changes in barometric pressure, intake air temp, engine coolant temp, etc.

For example, under the VE ECT Factor table, the factor value is set to 1 around the "nominal" operating temperature. Under the VE IAT Factor table, the factor is set to 1 around the "nominal" IAT.

I think most people just leave the factor tables alone and simply assume that they are correctly modifying VE.

One thing you could do after dialing in your VE is to create some log tables corresponding to the ECT, IAT, baro, and see if there are any significant errors and adjust that way. One word of caution on the ECT - at temps below normal (like less than thermostat open temperature) there are other modifiers functioning, e.g., FA Cold Enrich and Burn Fraction Inverse.

[skala308]

Thanks rockystock, yes I know about the multipliers, but have no clue what to do about them. I will study your advice. However, I am having problems with the bank 2 exhaust manifold leaking and also had a crack repaired. Still not correct and it is causing a lean condition in bank 2. So no point making any adjustments till manifold is repaired.

[rockystock]

FWIW, I was also having a lean error code on my bank 2, in the early days after swapping my hemi into a Jeep Wrangler with modified intake and exhaust. I did the due diligence and troubleshot the intake and exhaust, and found no leaks at all. I finally was able to get rid of the codes by getting the VE dialed in until there was no more than about 5% fuel trim error in every cell.

Another potential problem might be that your calibration may be missing some O2 sensor tables that can also help (possibly O2 goal voltage settings, etc.). Wouldn't hurt to compare your tune file to some others available in the Repository.

[pointofview_365]

That's exactly what I had to do myself with that pesky lean Bank 2 with my LT. So I had to part throttle adjust for winter and summer... On the safe side, I log my s1 with stft instead of ltft. For me, there's a very distinct pattern when it wants to go lean... Just adding to this thought...IMG_20210403_160007_618.jpg

[skala308]

Going to have the exhaust manifolds checked next week. As mentioned before, both left and right had broken studs and even small crack in right side (bank 2). Will log again and give feedback. However, just been on just over 2000km trip and got 7.6km/l fuel consumption, which to me is good

[Turbo2gnx]

ok i watched the video 3/4 so far and i checked my airflow at 10g/s at idle so is that almost twice as much needed for a 5.7?

[skala308]

ok i watched the video 3/4 so far and i checked my airflow at 10g/s at idle so is that almost twice as much needed for a 5.7?

I have not visited the forum for a while. Turbo2gnx, I have no idea what you are talking about, sorry cannot comment.

Since last post, manifolds sorted and also smoothed the VE tables alot and timing table some. Running great, until the main wiring harness from engine to transmission to PCM developed short circuit due to insulation disintegrating due to heat and wires chaffing on transmission. Came to dead stop and shutdown. Fixed few days ago and seems to be cured.

Will log some data and check.