KTM 990 Idle Speed Control Stepper Motor Operation

Discussion in 'KTM 950/990' started by BillyD, Jul 6, 2010.

  1. Salzig

    Salzig Long timer

    Joined:
    Oct 17, 2008
    Oddometer:
    1,238
    Location:
    Cremona, Italy
    "Zero position" is a simplified concept.
    Nothing forbids to have a set position different than "zero" (0 Volts in this case).
    chevtech likes this.
  2. rider911

    rider911 Shortcut Navigator

    Joined:
    Sep 18, 2009
    Oddometer:
    1,254
    Location:
    Australia
    Geez Steven go easy, the Wizard is still having trouble grasping the connection between the TPS and the throttle shaft.

    The ECU needs to see the stepper "read" zero before it allows a start

    Also if you dont understand what Steven just said, the TPS voltage has nothing to do with the stepper motor
  3. speedy 1

    speedy 1 Wizard

    Joined:
    Jan 26, 2013
    Oddometer:
    566
    Location:
    Dark Coast Southern Oregon
    Actually, I grasp the concept completely clearly.
    Perhaps better then most.
    The math in the ECU works from a floating decimal. Not a zero point.
    The floating decimal is derived from Throttle Position Sensor which happens to be an outdated technology that is easily contaminated with fuel fumes.
    When the TPS malfunctions it confuses the ECU which then sends wrong information to the stepper motor.
    The stepper gets lost and then pushes too hard on one end of the movement sending an error code to the dash and ECU.

    Plenty of history in this forum where dealer mechanics replace the entire throttle body because they can't figure this out.
    Or replace stepper motors because they don't know how to diagnose them.

    Bottom line ...
    If the bike runs erratic it's probably the TPS
    The TPS does not look to be a highly precision manufactured part, thus, new ones will probably have a percentage of failure.
    If it is only a 2% fail rate this means 2 out of 100 may not be good.
    So if the first TPS didn't completely fix the problem ... try another.
    Might be the reason Scuderia West keeps a half dozen in stock.
    Benduro and chevtech like this.
  4. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    The one serious question I have, is what role does the stepper play in the butterfly cycle at start-up? In other words, that throttle snap people are doing once they remove the stepper, is normally done by the stepper, and now you are doing it by hand! If you DON'T do it because it starts anyway, decent chance you are fucking up the base idle learn! That's assuming that snapping the throttle even duplicates what the ECU is looking for!

    Are we able to duplicate what it should see by just cycling the throttle? The ECU is likely re-checking TPS readings in that cycle and has anybody really figured what it is checking for? How do we know it isn't looking for the stepper to set the base idle above the throttle stop?!?

    Given that nobody has one of the fuel system engineers in their back pocket I have to assume no.

    Removing the stepper worries me for this reason.


    Todd
  5. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    Having said that, I'm likely going to remove it anyway, when that puppy kicks up when you were expecting engine deceleration coming hot into a turn, it's scary. These big displacement motors have SO MUCH deceleration if you are spinning over 7,500 RPM you really don't have to use the rear brake hardly at all! But when it's not there shitballs brother! it has almost caused me to lay the bike down twice, and I have only had maybe, 4-6 incidences of failure (that I noticed) in 10K miles.

    Scares the shit right out of me!

    :muutt


    :razor :topes


    Todd
    Benduro likes this.
  6. Parx400

    Parx400 Long timer

    Joined:
    Jun 17, 2010
    Oddometer:
    6,746
    Location:
    Sacramento CA
    I have a question. When the rpms are up does the stepper bottom back out? I have an issue when if rotate my throttle all the back back the bike will slow down mostly fine. If I do it really slow and hold it about 1% RPM it acts like one Cylinder has been cut. I was wondering if it’s possinle the butter fly is closing too far and when it gets to 0% throttle the stepper is opening it up a bit but At 1% it’s too far closed.
  7. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    Background on the bike setup?!? Tuned?!? O2 sensors still in play?


    Todd
  8. Parx400

    Parx400 Long timer

    Joined:
    Jun 17, 2010
    Oddometer:
    6,746
    Location:
    Sacramento CA
    No 02. I had a tune made and it could not be fixed. Bike is running burally rich on the front cylinder at 1% throttle. New tps, injectors cleaned and tested by a real shop. I have tried everything trying to fix this.

    You can see this when balancing the TBs. everything is balanced at idle. Soon as you touch the gas a hair it’s like it’s running on 1 cylinder till 2000 Rpm then snaps back and takes off.
  9. Parx400

    Parx400 Long timer

    Joined:
    Jun 17, 2010
    Oddometer:
    6,746
    Location:
    Sacramento CA
    Another question. Does the stepper set the position based on actual RPM or a position it thinks it should be based on temp?
  10. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    I don't think your problem is related to the stepper. I was going to recommend isolating the failed cylinder and systematically swapping components (injectors, coils, plugs) to see if you could isolate it to one of those components but a new throttle body (from your other thread) will eliminate much.

    I'd love to know the quantifiable answer to your dilemma though!

    ;)
  11. Parx400

    Parx400 Long timer

    Joined:
    Jun 17, 2010
    Oddometer:
    6,746
    Location:
    Sacramento CA

    I swapped coils, plugs and then had the injectors cleaned and tested by RC engineering. One of them was dripping so I was hoping that was the problem. It was not. New TPS right at .6

    The only thing I have not done yet is a leak down test.

    My uneducated throw shit against the wall theory is the front cylinder is hardly running until the throttle gets to 2%. You can see it go out of balance on the Tunemax, using a flow meter in the V stacks on on the map ports in tune ecu once you touch the gas. I also think but have no way of proving that my TB balance is way off. My theory is the front cylinder is starved for air and is pulling on the sensor and the balance port harder giving me a false reading. Anyways, I will report back when I have a chance to try the new set of TB's.
    Crazygreek and chevtech like this.
  12. chrisBTSC

    chrisBTSC Been here awhile

    Joined:
    Nov 8, 2006
    Oddometer:
    542
    Location:
    Folsom, CA
    Put in brand new plugs, start bike and let it run. Do not give it any throttle. Turn off the bike, pull the plugs. What do they look like? Are they the same color?
  13. StevenD

    StevenD Hmmmm, dirt!

    Joined:
    Aug 3, 2005
    Oddometer:
    1,505
    Location:
    Holland, Amserdammed
    Much easier to check egt..

    Verstuurd vanaf mijn SM-G935F met Tapatalk
    chevtech likes this.
  14. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    Cheap/compact infrared temp probe was on my travel list a year ago. Couldn't find one with a high enough temp range that was compact enough to carry. Might need to look again...they are so handy!

    :nod
  15. keener

    keener Speed changes you.

    Joined:
    Feb 24, 2010
    Oddometer:
    2,218
    Location:
    Toronto, Canada
    Have you check the play in the linkage ? It wears.
  16. rossguzzi

    rossguzzi 990 Adv.

    Joined:
    Oct 21, 2012
    Oddometer:
    2,633
    Location:
    Bottom left hand side of OZ
    Resurrecting a thread .

    I have a question for the brain here. My 07 990 in cold (first start) does not idle high. It just catches and idles at normal speed. Is this the ISC not working ?
    Rotty, 2nd flies removed, sas done, dongles fitted, Akras, custom map, new TPS set warm 0.6
    Bike runs good. Warm idle and start up just fine.
    Cheers
    chevtech likes this.
  17. chevtech

    chevtech Long timer

    Joined:
    Jun 14, 2016
    Oddometer:
    1,176
    Location:
    Hood River OR
    Did it ever work after said mods? The simple albeit undefinitive answer is most likely. If the TPS sensors and temp sensors (coolant and air) are reading correctly and the idle isn't kicking up than you likely have a bad ISC motor. However, you have lots of mods, and that introduces tons of variables that make it hard to anticipate their cumulative repercussions. In your case where it would appear to be dead completely this would be the time to use a factory scan tool, to command the stepper motor throughout it's range of motion. Seeing as how that isn't an option and you likely don't have access to a labscope that would let you see idle stepper inputs, you are reduced to your best guess.

    Sorry I can't be more help.


    :dunno
  18. kvango

    kvango Been here awhile

    Joined:
    Jun 28, 2014
    Oddometer:
    562
    Location:
    USA
    Wow, I have followed your issue - I see you are selling the throttle bodies you bought - no difference? What happens with engine vacuum as you crack open the throttle (1 vs 2)? Maybe equalize vacuum at 1-2% throttle? Have you tried TuneECU and opening up the L table for the offending cylinder? I noticed my maps are very different (1vs2)- if one cylinder was noticeably 'lagging' at off-idle - you can lean it out (if you are sure it is rich) at the offending RPM on the L (low) map.

    Well, if it has good idle when cold, then warms up - no problem! The idle/temp map is pretty gentle - I would assume it is working fine and closing the throttle a bit as it warms.

    IMG_1546.jpg

    Hey Todd -
    I noticed 'high RPM' throttle curves lean out pretty fast at closed throttle/high RPM's. . .If you have spare time on your hands, you could fatten up the higher RPM curves - but probably a better question for TuneECU thread rather than me guessing . . . .:dunno


    IMG_1544.jpg
  19. Themastermike

    Themastermike Think you caught me in a coma Supporter

    Joined:
    Jan 20, 2011
    Oddometer:
    2,901
    Location:
    So Ill
    Keep beating it but, synch the bodies?

    You old gauge method

    Sent from my XT1585 using Tapatalk
  20. rossguzzi

    rossguzzi 990 Adv.

    Joined:
    Oct 21, 2012
    Oddometer:
    2,633
    Location:
    Bottom left hand side of OZ
    Well, I backed off the return cable just a bit and it seems better. Perhaps it was a bit tight. Thanks !
    Themastermike likes this.