TNT 899 too low tick over when warm
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Thread: TNT 899 too low tick over when warm

  1. #1
    Junior Member Fabián's Avatar
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    TNT 899 too low tick over when warm

    Hi, I've been having an issue with my bike's idle speed since I bought it (used), now that I have the TuneECU software I'm determined to fix it
    The problem: the bike idles fine from cold to around 75c (1300 rpm steady)then, as the temperature increases the rpm drop to around 900 to 1000 rpm and it is quite erratic. Using TuneECU I found out that the stepper closes as the bike warms up which correlates with the rpm drop but why? It seems the stepper closes the air passage as the bike gets hotter BUT since the throttle bodies are all closed, too little air gets in the cylinders so the engine gets air starved.
    Lamba sensor reads .890 v. at idle.
    I tried turning the idle screw to increase it but that implied resetting the tps which caused an even more erratic idle speed.

    I'd like to understand the stepper function in all this, can I prevent it from fully closing ?
    Walbro ecu
    Thanks!

  2. #2
    Senior Member Rick67's Avatar
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    Hi Fabian.
    First of all what an interesting question..
    I'm assuming you have a clean air filter fist of all .
    And your right the stepper acts a cold start firstly then as the engine warms up it closes down so it's not running too lean.
    The ECU is supposed to then track the idle speed and adjust the stepper/timing and injectors to give a constant idle.
    Or so I've been lead to believe.

    I recently had the opposite problem after my stepper control housing fell apart , I had to buy another stepper motor from a triumph 955i. And also put the housing back together with super glue to prevent extra air being drawn in as I couldn't get the idle below 2,200rpm !.. it drove me nuts .

    So my thoughts are leading to the map you have installed on the ECU.
    it's quite possible that it's extremely Rich on tickover.
    I've noticed that you can can adjust adjust the tickover via the screw though.
    So why not just reset the TPS when the engine is hot and you've adjusted the tickover to a happy place ? .

    Hope this helps .. but I may be totally wrong .
    Rick

  3. #3
    Junior Member Fabián's Avatar
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    Hi Rick
    I always reset the tps when fully warm.
    I tried adjusting the idle fuel trim on TuneECU but it doesn't seem to have any effect on idle speed unless I change the values extremely to the left or right of the slider causing the bike to stall.
    I do think the map has something to do with the problem since I'm using the richest one available on the TuneECU page (tnt9402) I will try other maps today.
    What about the AIR screws that are located near the throttle bodies?
    Would they, being fully or partially closed, have any effect on idle speed?
    Should I try opening them a little bit more to see if it works?

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    GBo
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    They are a challenge to setup correctly
    This is what Alex at maniac told me to do

    idle should be between 2-4% tps opening for your Bike, the idle co level should be adjusted to 1,5-2,5% co at watertemp 90-98°
    usually this is around 0,930 in Tune ecu, setting for co correction is 0,945 in Tune ecu and should cause around 4%co at 3000rpm

    this is on a tre899k and it seems to work ok
    the screws are used to fine tune the throttle body balance

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    Junior Member Fabián's Avatar
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    I did what you suggested, and it worked!
    I have a normal idle at last!!
    Thanks!
    I still don't understand the function of the stepper on the 899 though. It seems to me that its only purpose is to act as a choke to help with cold starts. But nothing more than that.
    I've read that on other tnt's or tornados it does have a part to play in controlling the tickover speed at all times and it opens or closes there air passages to keep the idle stable and consistent no matter the temperature.
    What do you guys know about that?
    Is the stepper on the tnt899 only a cold start aid?

  7. #6
    Senior Member Engenia's Avatar
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    Errol Kowald
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    I have no experience with the Walbro ECU, but i suspect it is not too much different to the Sagem when it comes to idle speed control.

    With the Sagem,
    1. The throttles are adjusted as near as possible to fully closed. I test this with a strip of the finest paper I can find - the thermal print paper from an EFTPOS machine is about as thin as it comes. Using a strip ~10 mm wide, open each throttle in turn and place the strip between it and the body. With the butterfly closed, it should grip the strip. If that doesn't happen, adjust it until it does.That will close off the throttles, so at idle, the ECU must open the IACV (stepper) slightly in order to keep the engine running.
    2. With the engine off, connect vacuum gauges in the air lines from the stepper to each throttle. You'll need a T piece.
    3. Close off each bypass screw
    4. start the engine. It may not run smoothly, because it is not balanced.
    5. Check the vacuum in each air line and open the bypass screws of the highest two to equalize the vacuums across all three. One will remain closed.
    6. With the Sagem, you now adjust the CO to get the smoothest idle, or if you want, adjust the CO to the recommended value.
    7. Then you'll need to revisit the bypass screws - CO - bypass - etc until you've got it as good as it can be.
    8. Then in the Sagem you adjust the # steps to fall inside the recommended range. I think its called "offset" in TuneECU. I'm not sure if Walbro needs to do this.
    9. Check it all again - CO - balance - steps - and you're done.


    Without the butterflies fully closed the ECU will struggle to control the idle speed with the IACV.
    It also adjusts the ignition advance angle to control the idle speed, which it can do far faster than it can alter the IACV, so its a fine trimming process.

    Like I said, this is how I do it on the 900 Tornado, but it should give you an idea of how yours works.
    hooroo, Errol www.engenia.com.au [136,351 km - and counting .....]

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    GBo
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    I tried the sagem style setup and couldn’t get a reliable tickover. The walbro seems to need a very different approach. But the workshop manual is practically useless.

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    Junior Member Fabián's Avatar
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    Hey! Thanks for all your replies!
    I observed that the stepper tries to make slight adjustments to keep the bike idling when cold so if I fully (or almost) close the throttle bodies the steps required for stable idle will be higher, let's say 15 steps when cold, when I open the TBs let's say 2% the steps number will be around 8 or 9 steps when cold.
    The problem is that as the bike gets hotter the stepper gradually closes the air passages until it's at only 3 or 2 steps opened and the rpms at idle drop accordingly. So it seems the stepper can't keep the idle speed by itself on the 899 and needs the TBs to be opened to around 4% to let more air in.
    The stepper count can't be modified with TuneECU on the TNT 899 unfortunately.

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    Senior Member Rick67's Avatar
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    My understanding is that the throttle bodies are adjusted for tickover when hot then reset the TPS so at rest on a non running engine the TPS shows zero.
    That's how it is on my bike and it's worked perfectly that way for about 18000 miles of use.
    I now have a Walbro ECU from a 899 tnt I believe loaded with my map from old ECU , but now unfortunately I only have the ability to only access one map ,
    For some reason my tickover adjuster is now redundant and the stepper totally controls my idle speed . But it's steady at about 1350 rpm when hot so that's good enough for me .
    I've a feeling these bikes have a mind of their own and are totally unique from each other lol..

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