Tried out some 100 octane gas...

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Tried out some 100 octane gas...

This is a discussion on Tried out some 100 octane gas... within the Veloster Performance forums, part of the Veloster Turbo Garage category; Background: I have a 2017 DCT with 10k miles. Only mods are the bigger tb and a custom OEM replacement intake pipe with the stock ...

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    Tried out some 100 octane gas...

    Background: I have a 2017 DCT with 10k miles. Only mods are the bigger tb and a custom OEM replacement intake pipe with the stock airbox. My theory is that the car exhibits a few overlapping driveabilty issues and has since new. On the ECU side throttle response is non linear much of the time. There are times where the car will take off like a bat out of hell with just and inch of throttle. Ask for more throttle and it begins to feel like itís pulling timing in a jerky fashion almost as much as you are opening the throttle, so you donít increase your rate of acceleration anywhere near corresponding to the amount of pedal input.

    Iím on vacation and I thought it would be a good time to see if Nevada or Utah offer higher octane than Californiaís 91. Turns out that neither of them have 93, but a place in Nevada had 100. At $8/gal I figured what the fuck why not. I added about half a tank of 100 to about 1/8th tank remaining of 91 and set off to feel the difference. At this point I had an indicated range of 230 miles at whatever octane this mix equated to. Itís been interesting. Resetting the ECU wasnít an option I wanted to entertain, so I let the ECU adjust as I crossed the desert. First thing I noticed is the DCT began slipping. I thought this was good - the car was probably making more power and the TCU was going to also have to adjust. Initially the jerkiness remained, but it was severely muted. It would only pull timing for a split second. As the miles piled on all of the garbage ECU behavior went away completely. GONE. The TCU adjusted for the different power delivery and stopped the new slipping, although itís still the same TCU so it still slips when itís cold, for example. But the DCT was more consistent IMO because the ECU wasnít constantly fucking with engine output any more. But I couldnít trip up the ECU no matter what I tried. Half throttle, WOT at low rpms, gradually increasing from light to WOT, the car responds perfectly with zero hesitation. The trans would kick down a gear, then another, then another as I applied the throttle just as one would expect any auto trans car to.

    I have since had to refill with 91. Mileage seemed to drop a little while on the ~100 mixture, but that may have been me experimenting with WOT. On 91 the car seems a little better at very light throttle, and some, but not all of the hesitation has returned.

    Draw your own conclusions. My conclusion is that the OEM ECU tune is garbage. Not sure exactly how, or why, but it is. This is otherwise a car I really like and thatís a pity.

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    It's made for mpg, not power, or being linear to pedal, and 87 octane. Glad you realize stock tune is crap. Hope you realize the fuel is crap in cali as well.....
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    It’s made for higher than 91 octane, and that’s crystal clear. The ECU wouldn’t behave any differently on that higher octane mix otherwise unless there is some specific issue with my car that isn’t apparent.

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    Quote Originally Posted by Joe Schmoe View Post
    It’s made for higher than 91 octane, and that’s crystal clear. The ECU wouldn’t behave any differently on that higher octane mix otherwise unless there is some specific issue with my car that isn’t apparent.
    It's made for 87 octane and mpg. It just runs better on better fuel. But it's still crap.
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    Throttle cut implies itís not even made for normal driving with 91 octane either. Whatever their marketing or cost driven excuse is for their Ecu strategy the car does not deliver on a what I would refer as an acceptable driving experience with anything less than probably 93 octane. Again, unless I have a hyperactive knock sensor or something to that effect.

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    I don't post here any more because I can't stand most of the regulars here, but I am going to post a follow up in this particular thread for new people (since people tend to be referred here) who might encounter similar trouble. To recap my initial post: car exhibited very jerky and inconsistent hesitation. It also exhibited very sloppy upshifts. The car finally went into permanent limp mode a while back. Dealer diagnosed blown/seized turbo and replaced it under warranty. Initially upon getting the car back it behaved somewhat better. Some hesitation still present, but I noticed that each drive cycle the car behaved better than the last. I suspect the ECU was not reset after the tech finished. Although it felt pretty good I decided to reset the ECU. Now, after a few more drive cycles the car drives exactly like it should. Acceleration vs. pedal is nearly linear, with much better throttle response and much improved midrange. There is little hesitation left, and the clutches slip only a fraction of the amount they used to. My current theory is that while the turbo was going bad for whatever reason, the ECU was failing to compensate effectively. I also think the TCU was on the receiving end of the struggle from the ECU, and then executed sloppy shifts. The remaining slop in the upshifts tends to happen on even numbered gears, perhaps even-gear clutch actuator is weak/slow. I can't think of a reason why the car felt so much better on 100 octane if the turbo was going bad.

    Now, I don't really care for the input of the members here so I'm gonna bail on this board again right after this. But for any other DCT Turbo owners who seek answers here and have similar issues, you might look to either the turbo or it's associated hardware. Wastegate issue? I truly don't know.

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    The cars make more power and does so more efficiently on higher octane fuel. The TCU operates partially off how efficiently the car is making power which further supports how shitty the stock tune is for fuels the car may run on the daily. But also a large number of things could cause the same or similar issues that would be difficult to chase down.
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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