Negative Engine Torque at idle?

[Dominatorstang]

So I tried searching for this on this forum and on google, but it mostly just kept coming up with results focused on negative spark timing at idle since that is a such a common topic.

I understand the ECM calculates engine torque from things like the VVE, MAF, injector PW, and max torque spark timing. The thing is I am not finding exactly where my issue is that is causing it to show negative torque at idle. I figured it was the external load table from the little bit of info I did find, but it did not appear to change it very much.

The reason the torque representation being low is bothering me is that I feel like the transmission is not commanding enough line pressure during light accel and I do not want to be slipping clutches or causing any damage running it this way while I tune.

My attached tune below is far from complete, but I am wanting to to get the torque number in the positive before I keep going too much.

short cruise in town.hpl
disable DFCO using ECT this time.hpt

[Dominatorstang]

Well I think i figured it out. The airmass VT table I have was pulled from a different tune and changing it back to a near stock table brought me back into the positive on torque and the transmission acts much better on light throttle take off.

This also tells me that the way I was going to tune that table will not work.... I figured once I got VVE, MAF, fueling, and spark about right then I could log what the ECM was calculating actual engine torque and fill in those VT tables. But it is acting like those tables are used in part of what it calculates engine torque as?

testing with stock VT airmass.hpl
trying stock airmass VT.hpt

[smokeshow]

Was going to say...the airmass torque model looks negative in your idle region. Clearly changes have been made here lol. Noticed a couple things otherwise...looks like you haven't got around to correcting VVE for different cam positions. That won't affect your idle torque since it's just using MAF then...but it will affect shift quality as a shift is a transient maneuver and the MAF is largely ignored. Reason being...the cam is used as feed-forward torque control for shift torque management. If the cal is off in VVE where your cam is phasing (and it is...by 30-40%, I checked), reported torque will be inaccurate and affect the shift. Also...neeeever leave the virtual flex fuel algorithm active when calibrating airflow changes. If you're using fuel trim feedback to correct for airflow changes and the fuel feedback system gets hijacked during a forced ethanol learn...bad things are learned. So disable it and fix the ethanol content to whatever the concentration is while you're working on the airflow cal.

[GHuggins]

You need to adjust those vt tables to where your still running positive timing for your cam but showing around 15 to 20 positive torque. You can shift and dial them in for your application. Then as Smoke pointed out your VVE is very different now from your post a few weeks ago - you've lowered it substantially under what it should be in the lower load/rpm areas.

[Dominatorstang]

Thank you smokeshow and GHuggins. I had found the info explaining after a cam to lower VT in the idle area and work the numbers to get my spark advance numbers in the range like you mention. That VT table on the first post was part of that tune file that fixed up my idle surge on my old post and my idle spark stayed in an okay range with no more major surge so I had not given it much more thought until I was searching for the cause of why it just didn't feel right on light throttle takeoff. I am sure my bad VVE adjustments just made things worse too.

I had been out of date on tuning since ~2010 and mostly had knowledge up to Gen3, not that I was ever great at it. So now coming into gen5 on a 17 I find myself chasing my tail on many things. Like also I am unable to disable closed loop (besides in scanner) or DFCO (only tried a few things so far) and it appears that maybe this is just how it is on the E92A? So I just try and work around it like I assume everyone else does.

I think part of my issue with VVE is I kept trying to use the method I had back in 2010 on Gen3 (if my memory is even right). Now that I found the VVE+MAF writeup about a week ago, plus a good steady state filter, and disabling the virtual flex fuel then I think I can stop messing up that table... The DFCO staying active still messes with me when it comes out of DFCO because it throws a bunch of positive numbers in that my filter is not blocking. If I can not get it to disable then I guess I just need to filter it out better.

Also looking forward to VVT tuning and trying my hand at SOI tuning once I get to that stage.

[GHuggins]

That soi table I gave you a few weeks ago should just about be optimal for your current setup. With a good spark timing map, your truck should run like a raped ape so to speak

For the vve calculations use the cyl airmass calc. It doesn't rely on the MAF being 100% perfect.

[Dominatorstang]

Okay thank you GHuggins, I will switch back to those tables and use cyl airmass calc. Reviewing through the VVE+MAF writeup, it uses the cyl airmass calc you are talking about right?

The truck did feel really strong with those. Me not tuning VVE correctly kept giving me mixed results to where I started changing other tables and digging a hole. Thanks for helping to pull me back out of it.

[GHuggins]

Shoot me an email listed in my sig. If your running 93 or even if your not I can send you the optimalish spark tables too. I like using the airmass calc even though I chart a couple of them and average the maths together just because the others have to be done 100% in steady state. The airmass calc uses other variables to smooth things out a bit better - just in my opinion and from what I've seen.

[Dominatorstang]

GHuggins, are you saying 15-20 when idling in neutral/park or in gear?

adjust those vt tables to where your still running positive timing for your cam but showing around 15 to 20 positive torque

Also I have begun tuning the rest of my virtual torque tables using delivered engine torque from my logs. Do you still recommend this method as you did a few years back on Gen4?

[GHuggins]

The load tables for torque in the idle section are going to go hand and hand with the tm. Yes try to keep tm close to slightly over actual calculated engine torque if you can - this is mostly for trans life.

[Dominatorstang]

Okay, got it. Thank you!