Author Topic: Light throttle surging  (Read 204 times)

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Offline Steve in sunny Fla

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Light throttle surging
on: July 11, 2020, 04:24:01 PM
  I had a conversation with another member yesterday about light throttle surging. Let's say you're riding in your neighborhood, light throttle, 30 mph or so... you feel that constant surging from the engine. it's unsettling.

  That surging is coming from the ecu going into closed loop mode, and attempting to trim the fuel to a 14.7 average stochiometric value. We can call it AFR... air / fuel ratio.

   The problem is 2fold. First, particularly in the US where we have 10% ethanol fuel, the stoic value isn't 14.7. 14.7 is to lean. So when the ECU is trying to correct to that value, it IS correcting to a value that is on the lean side. Secondly, the way narrow band 02 sensors operate, they aren't really "holding" the AFR at a steady value. They shoot the values rich and lean, and try to reach the middle ground of .45 volts (14.7 afr or lambda for gasoline) as an AVERAGE. So probably half the time you're running in closed loop you're even leaner that 14.7, but remember it's like this /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ . To top it off, there are times that a stoic value is just to lean for the engine to be happy. For example 14.7 at idle will not produce a strong idle on this bike... it needs to be richer.

   Folks think that if you change air cleaners or exhaust, the 02 sensor will adjust for that. Not so. The sensors have a range from the base table of perhaps 5% - 8% . ... and remember this is ONLY for closed loop operation, generally based on the rpm of ignition events. When you are accelerating for example, the ecu kicks out of closed loop and your fueling reverts to the base fuel table with adjustments for ambient temp, engine temp and altitude. Again, the sensor only adjusts when you are in closed loop operation, which generally means light throttle, steady rpm cruising. And that's exactly where you feel the surging.

   I hope this has cleared up any misconceptions, and help you understand where the surging is originating from.

  Steve

Offline Maverick

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Re: Light throttle surging
Reply #1 on: July 12, 2020, 01:04:53 PM
Glad mine doesn't do that.

Offline Bigpadg

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Re: Light throttle surging
Reply #2 on: July 12, 2020, 01:16:05 PM
Very good info, Steve. Thanks for taking your time to educate and inform us in such detail - it really is helpful in determining what needs to be considered in improving our versatile mounts.
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Offline Steve in sunny Fla

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Re: Light throttle surging
Reply #3 on: July 12, 2020, 01:45:54 PM
*Originally Posted by Maverick [+]
Glad mine doesn't do that.

   Are you running pure gas, not 10% ethanol? I'm curious how much the ethanol in our US fuel could contribute to this.


Offline Maverick

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Re: Light throttle surging
Reply #4 on: July 12, 2020, 02:47:32 PM
I refuse to run ethanol unless I have no choice AND I use that tank of fuel the same day.

Online uralrob

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Re: Light throttle surging
Reply #5 on: July 13, 2020, 02:02:39 AM

 I don't get the surging and use premium fuel, 91 ron/mon here, which is reputed not to have any ethanol. It is clear rather than having the greenish tinge of some ethanol laced fuels.

 Rob.

Offline maine_man

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Re: Light throttle surging
Reply #6 on: July 26, 2020, 01:18:56 AM
Is this surging something your ecu flash solves?
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Offline Steve in sunny Fla

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Re: Light throttle surging
Reply #7 on: July 26, 2020, 04:18:11 AM
 Yes. My bike did it. Others who have gotten my flash had it also.

   When it comes to tuning though, sometimes I talk with folks who totally get it and others that don't have a clue. Some folks feel changes when there are none, some folks don't feel things that are very real and present.

 Steve