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Thread: LSA goes lean when coasting, DFCO off

  1. #1

    LSA goes lean when coasting, DFCO off

    Trying to do MAF cal after doing a bunch of things. I let the car get to operating temp, start the log, and everything looks good. Idle cells within 2-3% of what I'm after. Driving around everything looks good, WOT looks good, but on coasting/decel, it goes super lean, at least 19:1 which is as high as the wideband goes. This is seriously skewing the idle cells in the maf error log and I'm unable to get them set where I want them lol


    Any ideas? Just realized I have the tune and last log on the laptop, so I'll post those in a second.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  2. #2
    The tune file and last log.
    Attached Files Attached Files
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  3. #3
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    Just put a simple filter in the scanner...ignore all data below 30kpa or something.

  4. #4
    Quote Originally Posted by smokeshow View Post
    Just put a simple filter in the scanner...ignore all data below 30kpa or something.
    Short term that would be fine but it keeps me from logging idle flow. I think I figured it out though. Since it was only going lean when coasting if I didn't clutch in, and went back to normal with clutch in/engine at idle speed, I set out with some brake cleaner and found #1 injector oring leaking. At idle it barely stumbles, but I imagine at 3-4k rpm under vacuum it leaks bad. This would mean I also have a boost leak, so maybe I'll pick up a tiny bit of power as well lol
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  5. #5
    I got that oring replaced, but it didn't fix it besides a slightly better idle. Doing some more logging, I've found that it does it no matter what, as long as it's in gear and coasting. Cruise on or off, any gear, any speed, any rpm. I even lugged it down to 500rpm and it still does it. I turned the DFCO back to stock settings, flashed it, then disabled DFCO and flashed it again, and it actually started working again for about 3 miles, then went back to the lean coasting. I have no idea what to check next. It is pulling fuel down to the minimum IDC that I set with the new injectors, which is .300, but it idles at 1-1.1. So I at least know this is 100% tune related now.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  6. #6
    So I've found a very old thread that mentioned transient fueling can cause what I'm seeing. Time to research some more.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  7. #7
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    Shouldn't be transient fueling. The puddle dries up, regardless whether or not DFCO is enabled.

    Speaking of DFCO...as a bit of history, it didn't originate because the manufacturers wanted to save fuel. What they wanted to prevent was extreme low load partial misfires due to combustion instability. You can imagine the flame doesn't move too well when the cylinder is drawing from a manifold at 20kpa. DFCO just removes the combustion entirely so you don't get a misfire, you get no fire. And thus less emissions. But in your case, because it is still partially misfiring with DFCO disabled, tons of unburned oxygen makes it out of the exhaust. So it looks lean. Question is...is it causing any problems other than messing up your histogram?

  8. #8
    Quote Originally Posted by smokeshow View Post
    Shouldn't be transient fueling. The puddle dries up, regardless whether or not DFCO is enabled.

    Speaking of DFCO...as a bit of history, it didn't originate because the manufacturers wanted to save fuel. What they wanted to prevent was extreme low load partial misfires due to combustion instability. You can imagine the flame doesn't move too well when the cylinder is drawing from a manifold at 20kpa. DFCO just removes the combustion entirely so you don't get a misfire, you get no fire. And thus less emissions. But in your case, because it is still partially misfiring with DFCO disabled, tons of unburned oxygen makes it out of the exhaust. So it looks lean. Question is...is it causing any problems other than messing up your histogram?
    Yeah after looking up some more, it seems like those people with trans fuel issues were just having lean spikes on decel, not constant lean like mine.

    I kinda figured DFCO was an emissions thing, and not actually for efficiency lol.

    It makes it try to stall sometimes when coasting, and getting back in the throttle it sometimes sputters. And it's definitely going to screw with fuel trims once I turn those back on.

    I just don't understand why it's doing it now, but wasn't before the injectors and headers. I kinda want to raise the minimum injector pulse from .3 up to 1ms where it normally idles at, but I'd consider that cheating and hate to even think about it. For a short minute, I figured it was injector related, but it functions perfectly in every single other function.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  9. #9
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    Quote Originally Posted by madmikeismad View Post
    Yeah after looking up some more, it seems like those people with trans fuel issues were just having lean spikes on decel, not constant lean like mine.

    I kinda figured DFCO was an emissions thing, and not actually for efficiency lol.

    It makes it try to stall sometimes when coasting, and getting back in the throttle it sometimes sputters. And it's definitely going to screw with fuel trims once I turn those back on.

    I just don't understand why it's doing it now, but wasn't before the injectors and headers. I kinda want to raise the minimum injector pulse from .3 up to 1ms where it normally idles at, but I'd consider that cheating and hate to even think about it. For a short minute, I figured it was injector related, but it functions perfectly in every single other function.
    Probably the injectors, honestly. The LSA really is supposed to have an offset injection angle due to the injector boss orientation in the blower. Otherwise they spray at the port wall and make tip-ins lean. Fortunately you have the best injectors you could get for transient response in the LSA, aside from stock; I ran them myself on an LSA and was blown away with how good they were compared to what I expected. I still had to tweak transient fuel a bit, but because they atomize so well the wall wetting impact was far less. I did run more fuel pressure than you do though...may benefit from bringing that up a bit, especially since it isn't boost referenced.

  10. #10
    Quote Originally Posted by smokeshow View Post
    Probably the injectors, honestly. The LSA really is supposed to have an offset injection angle due to the injector boss orientation in the blower. Otherwise they spray at the port wall and make tip-ins lean. Fortunately you have the best injectors you could get for transient response in the LSA, aside from stock; I ran them myself on an LSA and was blown away with how good they were compared to what I expected. I still had to tweak transient fuel a bit, but because they atomize so well the wall wetting impact was far less. I did run more fuel pressure than you do though...may benefit from bringing that up a bit, especially since it isn't boost referenced.
    I do love these injectors. I scaled them 50% of the chart they gave me, used a 2x multiplier in the voltage modifier, and they fired immediately and ran like stock. Fricken love them. Transient fuel is still something I don't know crap about, so I really need to get on that. For fuel pressure, I'm still at 65psi, but it spikes to 85 when the aux pump kicks on until rev'd out and it settles around 68ish. I haven't figured out how to combat that yet, it's like the stock pump/module can't turn down enough to keep the pressure in check.


    Regarding my original issue, I've discovered something else just by sheer luck. So it will do the lean coasting in any gear with the clutch out. I never thought to do it in neutral with the clutch out, and turns out it doesn't do it. Even at the same rpm and same speed, it only does it if it's actually in gear. I noticed as well that the tps drops to 20% when in gear, but back up to 24% when in neutral or clutch in. I'm at a loss here. Ready to pull my last few hairs out.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  11. #11
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    Quote Originally Posted by madmikeismad View Post
    Regarding my original issue, I've discovered something else just by sheer luck. So it will do the lean coasting in any gear with the clutch out. I never thought to do it in neutral with the clutch out, and turns out it doesn't do it. Even at the same rpm and same speed, it only does it if it's actually in gear. I noticed as well that the tps drops to 20% when in gear, but back up to 24% when in neutral or clutch in. I'm at a loss here. Ready to pull my last few hairs out.
    Post up this data.

  12. #12
    Quote Originally Posted by smokeshow View Post
    Post up this data.
    Will do tomorrow. I'll get a video so you can see exactly what I'm doing and when.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  13. #13
    So I'm an idiot. I looked through some old logs from when it was intake only, and it still did this sometimes (not everytime, but it did do it), and only when I was maf only. SD only it worked fine. So I guess I'll just make the adjustments to the loaded part of the map for now, and then adjust idle in a separate session so it won't skew with coasting. I'll get the bottom of the map as close as possible and then just be stuck with running vve tables too.

    One thing this experience has taught me, is that I really need a fricken dyno.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  14. #14
    Senior Tuner DSteck's Avatar
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    Edit the FPCM, and you can control pressure better. You can’t fix the spike, but you can settle it a little faster. The beauty of live fuel pressure reporting is that you get live fuel pressure reporting.

    Editing the FPCM will allow you to run 500-550kPa pressure during WOT.

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  15. #15
    Quote Originally Posted by DSteck View Post
    Edit the FPCM, and you can control pressure better. You can’t fix the spike, but you can settle it a little faster. The beauty of live fuel pressure reporting is that you get live fuel pressure reporting.

    Editing the FPCM will allow you to run 500-550kPa pressure during WOT.
    Are you referring to my pressure spike when the aux pump kicks on? I didn't even think about just raising base pressure, but that makes a lot more sense lol

    EDIT: so I can actually go to 297psi with this car. I should be able to get this sorted out now.
    Last edited by madmikeismad; 07-02-2020 at 11:26 PM.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block

  16. #16
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by madmikeismad View Post
    Are you referring to my pressure spike when the aux pump kicks on? I didn't even think about just raising base pressure, but that makes a lot more sense lol

    EDIT: so I can actually go to 297psi with this car. I should be able to get this sorted out now.
    Definitely don't request more than 550kPa in high flow. The in tank relief will kill things at about 580 anyway, and there's no point in trying to ride that relief.

    DSX Tuning - Authorized HP Tuners Dealer
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  17. #17
    Thats exactly what I went to for high flow lol.
    '12 ZL1 - RPM 5", TSP 2" headers, Speed Engineering 3" header back, Dayco 8.66 lower/LPE 2.38 upper, ID1050x's with DSX aux kit and E, NGK TR8's, Taylor wires, 160* tstat, NW 102, self ported snout/blower, Stock unopened long block