KTM 790 takes a few tries to start

Discussion in 'Parallel World (790/890)' started by doctorblanco, Sep 10, 2019.

  1. WI-790R

    WI-790R Been here awhile

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    The components from Mouser arrived first today, so I soldered up one board after supper. I appreciate even more now, the surface mount placement equipment and reflow ovens at work! I didn’t have solder paste and hot air soldering equipment, so made do with a conventional iron with small tip and solder wire. Someone 1/3rd my age might have less trouble soldering U2. I worked under a cheap usb microscope that has quite an image delay.......

    With the IAT sensor removed from the bike & wired to the dongle, and a 2.15K resistor in series with the dongle to a 5v supply (to emulate the pull resistor in the ecu) I measured 3.46v for about 10s, then it drops to 2.55v. I didn’t have a thermometer at the table where I was working but it felt about 74F I’d guess. The TSTAT on the wall some distance away, showed 72F. At any rate, those measurements agree pretty well for what I was expecting at that temp. Those numbers equate I believe, to a simulated air temp lower than actual, by an amount to request 7-8% more fuel.

    Do you think for this dongle experiment, that 7-8% is enough? Or should I go big or go home...... I could change the onboard thermistors to a higher value resistance, to say double that amount.

    17517F33-F1BD-480D-8708-4907D9240BD9.jpeg
    konam, Salzig, SoilSampleDave and 2 others like this.
  2. Gaulin

    Gaulin Orange (& Blue) Crush

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    While first reading this, admittedly my immediate thought is another voodoo magic method....

    But thinking it through, perhaps by letting the fuel pump get to pressure as normal, then cycling the kill switch, the fuel pump will be running at the same instant it's turning over. Giving that little bit of extra fuel it needs ? Just thinking out loud....

    A lot of these fixes often work at the time, but then over the course of several months/ kms the problem returns. Let us know if this still works over the long haul.
    Matthewm likes this.
  3. windblown101

    windblown101 Long timer Supporter

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    @WI-790R

    Awesome work. I would not go any further with the fuel enrichment based on what I've experienced. It really is a close thing. Go higher and you might induce starting problems with being too rich.

    Just a seat of the pants guess though. You're the mad genius at work! :)

    The only other thing I thought about just now is your timing circuit. I'm guessing it powers up and starts the countdown when the ignition is switched on? If so, how long one takes between ignition on and pressing the start button becomes a variable to how long it enriches the circuit, yes?
  4. LikeTheAspirin

    LikeTheAspirin ... please, after you.

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    These recent "this is what's working for me now" posts all sound similar to 9.5isCanadian's shut down procedure posts from weeks ago. Again, maybe the computer will learn and it won't work after a month of doing it regularly. But the bike seems to like a post shutdown fuel prime. Don't know enough about engines to know if that all gets sucked out by vacuum during the next start up and is voodoo magic or if it is more simply more gas = more better.
    lithodave likes this.
  5. WI-790R

    WI-790R Been here awhile

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    You probably got the mad part right! On the timing, yes, exactly like you described. The ecu’s 5v supply powers up as soon as the key is turned on, so if you waited 10s before pressing the start button, no extra fuel will be given. With this simple circuit, the timing is set by the value of capacitors and a resistor. The capacitors charge through R3 from the pull-up in the ecu. When the capacitor voltage reaches the reference voltage inside U2, the output (labeled RESET on the schematic symbol) changes state, allowing Q1 to be turned on, which shorts across the thermistors, dropping the fuel request back to normal levels.

    We could make the timing begin when the button is pressed if we wired in to the starter circuit. I was trying to avoid having to tap in to the bike’s harness in multiple places. Is a count of three from when the key is turned on, about what it takes for the pump to stop?
  6. TrailTrauma

    TrailTrauma Nemophilist Supporter

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    @WI-790R what if you incorporate a few thermistors into the product or one and a small pot or multiswitch which allows riders at different altitudes/countries to customize it for their needs. Or poor fuel on international trips, and so on.
  7. WI-790R

    WI-790R Been here awhile

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    Electrically that would be easy enough I think. Keeping water & mud out of a dip switch and circuit sounds challenging to me(?). I was thinking this little board could be protected with a piece of 12mm/0.5” heatshrink, the kind with adhesive inside. I was picturing the two pairs of wires, each in their own sleeving, being sealed by the heatshrink glue where I’d squeeze it with one of those sheet metal vice grips (while the glue is still hot). I have not tried that yet to see if it works.... I was headed down a path that wouldn’t require any molded parts, etc.

    I have a power commander and wideband O2 module on a Grom. I believe one of those has a dip switch covered by a rubber flap or something. I’m sure there’s a way it could be done.
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  8. Salzig

    Salzig Long timer

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    Only part number I found is this 6189-0156. I stopped searching because I only found either chinese selling sites or ebay/amazon ads for like 100 pieces. Not to mention I don't own a 790 :D

    RE waterproofing, with my Side Stand Sensor Eliminator circuit (SSSE© :lol3) I covered the board with Plastidip (a gummy insulating/waterproofing paint), wrapped it in heatshrink, pinched the ends with pliers when still hot and again Plastidipped the ends.
    IMG_20181105_165603.jpg
  9. WI-790R

    WI-790R Been here awhile

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    That looks sealed up really well.

    edit to add: Thanks for reminding me of that part number you posted. I searched on it again, this time looking at images. I just placed an order for what I believe to be the male mating connector from https://www.auto-click.co.uk.

    I’m half expecting for KTM to issue a firmware update to fix the starting thing any day now. What better way to expidite that than by making a dongle, right?
    Salzig likes this.
  10. SoilSampleDave

    SoilSampleDave Dr. Zaius was right!

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    Now we see the true depths of your mental health issues!
  11. WI-790R

    WI-790R Been here awhile

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    I know, right! The Grom experiment was to add sufficient power to make it comfortable in 60mph 2-lane traffic. It’ll do that except if trying to buck a modest headwind. Then I have to get into a partial tuck. It’s 183cc now, different bore, head, cam, throttle body, air intake, exhaust, gearing, handlebars, mirrors, oil pump, side cover, and the fore mentioned fuel management stuff. I’m sure I’m forgetting something....
  12. SoilSampleDave

    SoilSampleDave Dr. Zaius was right!

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    :loco
  13. Marcham

    Marcham Been here awhile

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    3 days, 3 perfect starts using the new shutdown procedure. This w-e I'll go back to normal just to see....
  14. Dan D.

    Dan D. Long timer

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    The witchcraft method worked for me today... Mine has been acting up again lately.

    I think the secret is to have multiple tricks, and once the bike learns one, switch to another. Lol..


    https://youtube.com/EFqOrvsg9Ms
    gar likes this.
  15. 9.5isCanadian

    9.5isCanadian "Missing a few pieces." Supporter

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    Mine has been consistently starting since I adopted my Voodoo technique.
    :pope
    Should it act up again, I'll post up and report.
    9 1/2
    Marcham likes this.
  16. Juozaz

    Juozaz Juozaz F800GS Blonde

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    Agree, its works. Thanks bro
  17. Dan D.

    Dan D. Long timer

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    That technique failed for me today. Only one stall though.

    Again, not a big deal... Just sharing my experience.
  18. hcd

    hcd Been here awhile

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  19. WI-790R

    WI-790R Been here awhile

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    Right. I just say that jokingly since I laid out a circuit board and ordered connectors, based on a hunch that more fuel will help. You know how things go sometimes. You can’t find your flashlight so buy another one. Of course when the new one arrives, then the old one turns up....

    The circuit’s working the way I envisioned. I’m just waiting for connectors to arrive. My bike isn’t a very good test victim since it rarely requires a 2nd press of the start button. I’d like to send one out to someone who’s bike always needs multiple attempts, to see if this helps or not.
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  20. 1coolbanana

    1coolbanana Long timer

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    What an awesome effort :clap
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