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Thread: VVE Calibration timing issue

  1. #1

    VVE Calibration timing issue

    I am currently tuning a customers 2014 Silverado 5.3l, ported heads, mild cam, and headers. I am new to tuning gen V, I have tuned multiple gen 3 and 4 without issue, but I am running into an issue where when I disable the maf to tune speed density fueling, its trying to throw around -20 to -30 deg of timing at idle, causing map to be around 80-90kpa and glowing the headers.

    I have already calibrated maf without issue, idle timing in maf only mode doesnt ever go negative and idles right on target.

    Off idle seems to be okay aside from fueling not dialed in yet. At this point i had not seem the slightest bit of knock retard. I figured I would try taking some fuel out and the truck then idled okay, timing moving right around 0 deg. As soon as I put it in drive though, it started pulling timing again and threw up to 11 deg of knock retard, this still being at idle just in gear.

    Loaded the maf only tune back in and the truck acted completely normal. Both of these tunes are identical aside from one having speed density disabled and one having maf disabled. Also fuel trims are only around -10% on vve, which should in no way cause this.

    I do still have some work to do on the torque calibration and I understand that if its calculating more than expected it will pull timing, but it goes the complete opposite way between vve and maf with all other settings including torque the exact same.

    Is the process of disabling maf different between gen 4 and 5 or am i just missing something?

    Ive attached 3 logs, one from the first vve cal attempt without any fueling changes, one vve cal after i took fuel out and getting idle KR, and one on idling in maf only mode and putting it in gear. Also attaching the tune with maf disabled.
    Thanks
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  2. #2
    Tuner
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    I think you should look into tweaking your virual torque tables under the edit tab since the bigger cam makes less torque at idle those numbers need to be lowered in the idle regions. You may want to research exactly how to do that first, i'm kind of reciting what I seen other people have success with on here.
    14 GMC sierra 5.3

  3. #3
    Advanced Tuner lt1z350's Avatar
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    I spent all day well last two days fighting this myself so that I felt comfortable enough to not kill the header gaskets again and get enough timing into it in SD. What seemed to work best is go into virtual torque under map group and decrease the torque at your kpa and idle rpm. I looked at your tune and its a lot higher then mine is I have a decent size cam 227/244 on a 118 with 0 over lap and still had to do a ton of work to make it idle with even -5 to 10 degrees as its up and down but good enough to at least do some vve logging and make that better. the problem is as you can see on your logs when it retards the timing it drives the cylinder airmass up and the kpa goes up so it then skews all kinds of other tables. Yours seems to idle well in maf mode but getting the vve correct will help it drive better and make the transmission shift much better I will say that from experence and having to fix virtual torque on a lot of tunes for people that the car ran good but trans was very lazy and even slipped on some of these higher hp cars with big cams and a good set of heads. here is a screen shot of my table. I have my tune posted on the otjher thread talking about idle timing too thats near the top if wanted to look at it. i was as low as -20 and now am just above positive which is good enough to go drive and tune now. I hope my logs look as good as yours when I add the maf back in as yours idles well with the maf.
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  4. #4
    Senior Tuner eficalibrator's Avatar
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    GENV torque based systems don't have an idle spark table like GENIII/IV. They calculate the timing based on the torque model AND MBT reference. Both of those will need some adjustment on your new head/cam combo. We cover this in our training on the streaming site if you want the full explanation.