Tuning for lean cruise
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  1. #1
    The "Friends" of Officer Frank Poncherello POWER-TRIPP's Avatar
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    Tuning for lean cruise

    Before we get started, do yourself a favor and get a good shop to tune your bike to best performance at all engine speeds and loads. While this is not mandatory, it does give performance and drivability improvements and makes riding more enjoyable.

    [I take no responsibility for those that screw up their bikes by tuning too lean at the wrong time and load. If you go too lean where the bike is under load, you will feel the hesitation and misfires, and can damage the engine.]



    Running at part throttle, the engine is under low loads and is not filling near its potential. The cylinder pressures are much lower than at wide-open throttle (WOT), as well. As a result, the engine is much less sensitive to detonation. It is this exact reason that some of the newer automotive engines use variable compression ratios that run considerably more compression at part throttle than at WOT.

    Many engines are tuned from the factory to run lean at idle and light loads (cruise) in the region of AFR 14.57:1. This is for one reason, emissions. To keep the stock catalytic converter (cat) as efficient as possible, the exhaust gases need to be 400°F-600°F for light off, and a bit higher for best efficiency. Also at ~14.57:1 AFR the engine is at or near stoichiometric mixture and produces reduced hydrocarbons (HC) and nitrogen oxides (NOx) that are easy for the cat to burn off.

    The problem is that this is nowhere near the potential for best economy. Most engines can easily run as lean as AFR 16:1-18:1, and some even leaner, at low load and cruise, before lean misfires occur with any great number. Engines with high output CDI ignitions can easily be run at low load as lean as 22:1, and I have seen many run leaner than 26:1. THIS means that at low load we can tune the EFI to run much leaner and gain very good fuel economy while cruising, and still have great WOT performance. And this in no way harms the engine.


    So how do we go about tuning for lean cruise conditions?
    The ECU will try to keep the engine at stoichiometric fuel mixes at low throttle/load and engine speeds. In Tuneboy, you can alter the AFR tables so that the cells in the regions at cruise are much leaner, but the narrow band Lambda sensor (some mistakenly call this an O2 sensor) will not work at the lean mixtures we need. SO we really need to just turn this off. This can be done with TuneEdit on some ECUs for some models, but for PCIII users and bikes where TuneEdit cannot shut down the Lambda sensor you need to use a Lambda sensor bypass module. A few internet searches will locate one with the correct plug, or a generic one that you can wire in place - look at the units for the Power Commanders.

    On bikes with wideband sensors, simply clipping the power wire to the sensor's heater unit will disable it without causing a check engine light (CEL). You can later add a plug to this wire when you sell the bike. [Got a Ducati 1098, and can't tune under 40% throttle? This trick will get you fixed... you can just send me a check or PayPal for this one... no donations refused.]

    Now we can get to work.

    [The basic overview is that we are going to tune the idle and a couple of specific parts of the map at low loads until we get lean misfire. Then we will richen it back up a small amount. My bet is that many will go leaner, but will chicken out before they find just how lean they can actually run.]

    The next time you are out on the bike, pay attention to the speeds you run while cruising. My bet is that you run at one speed around town while in traffic, and another when on the highways or interstate. Lets say that these speeds are 40 mph and 70 mph. These are now going to be your target speeds where you know you will get good mileage.

    Now we need a way to see the exact rpm and load that the engine is under when cruising at these speeds. If you have Tuneboy or a PCIII, you can open the tuning software in a laptop and see the exact load cells affected in the fuel and timing tables while cruising. This works great on the dyno, but riding down the interstate at 70 mph with a laptop in front of you is neither safe nor smart. A much better idea is to use an OBDII scanner connected to the bike to read. You can buy a cheap one that will display the required information for around USD $100, or rent/borrow one from a local automotive supplier that rents tools (Some NAPA, Autozone, etc. stores). I place a couple of strips of Velcro on the back of the scanner, and use an elastic band that the scanner Velcros onto on my left leg (or that of a customer). You might even come up with a better idea.

    If you spend a good amount of time riding with a passenger, or loaded with bags and gear, the engine will be under more load, and different areas of the fuel tables will be used. It is a good idea to either tune these areas for lean cruising, or at least make sure they are different from the ones when riding solo or without gear.

    Look at the scanner while riding on both flat and hilly roads at your cruise speeds. Get the exact rpm, throttle position(s), MAP sensor load(s). Make sure the throttle position percentage(s) is/are the corrected ones the ECU uses, not just the uncorrected TP%.

    Now we can tune on a good loading dyno, or on the road.
    In the tuning software, locate the tables for ignition advance and the correct cells for load/TP and engine speed (rpm). Retard (reduce) the ignition advance 5-7 degrees. This will give us some room for safety.

    Look at the fuel tables and locate the cells for rpm/load/TP and reduce the numbers by 5%. Then test this area on the dyno or on the road. You are trying to notice any misfires caused by being to lean.
    With a multi-gas analyzer or a scope, these can be detected easily, but can be hard to detect on the road. If you have noticed misfires at idle, you get the idea what to look for.
    If misfires are detected, richen the cells by 2-3%.

    If no misfires were detected, you can lean the cells again, but this time we are going to go by 3%, and then test again for misfires. If no misfires are detected, again we can lean out the cells by 3%. Do this until misfires are detected, and then richen by 3%. This is it.

    You may need to adjust the timing for best results. Testing should show if more advance is an improvement. But do not exceed the advance of the original tune - likely this will be too much.


    Now, to smooth out the throttle transitions, we need to enrich/increase the acceleration compensation until the engine pulls smoothly to higher engine speeds and load/throttle. Hesitations in acceleration are caused by being too lean, and are easy to notice.

    The ECU will tend to adjust the running of the bike in the regions in and around the lean cruise region based on its interpolation software. Some ECUs have much stronger interpolation ability than others, so differences will crop up. You will have to tune and test a bit for best results. But for best results when riding, do not run at lean cruise and suddenly go to WOT. Slightly increase engine speed and load a small amount, and then you can grab a handful of throttle.

    It can take a good bit of work to get everything correct, and you may find it good to save the tuning files as you make adjustments in a special folder. Just save each time you make a change.


    Now you have taken advantage of the benefits of tuning EFI/engine management systems that many overlook. Power AND economy.

    As a side note - realize that you still will spend a good amount of riding outside of the regions where you have tuned for improved fuel economy. So the way you ride, will alter the fuel economy results.



    I hope this helps.
    "To succeed in this game, you have to dabble in the boundary of disaster." -Sterling Moss

    "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!', but 'That's funny…'" Isaac Asimov

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  2. #2
    The "Friends" of Officer Frank Poncherello Jaket's Avatar
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    Re: Tuning for lean cruise

    I think speedy gets hesitation quite fast when leaned out. when I was using Harri's eco map, I had to richen couple of cruise areas up, because it felt little hesitant to me.

    even before misfiring the good mixture will burn more efficiently. lean mixture is harder to get ignited, so you may end up with bigger throttle input to get the same power to reach that 60mph.

    lean mixture would also need higher ignition advance, because it doesn't start burning so easily or as fast?

    I had one BMW car and I made the mixture richer by adjusting the AIR meter. it made it more powerfull, and also got better fuel efficiency.
    http://corecatcher.wordpress.com/ <-- all my Triumph maintenance articles are here.

    2005 1050. black fat bars, hugger, frame protectors, headlight fairing. Motech Alu-rack. Smoothed TB's. MIVV GP carbon, headers smoothed/ported, precat removed, Modified Arrow tune. Sargent seat. GSG-moto generator- & front axl sliders. Frame sliders. GSX-R brakes with 1000RR master cylinder. Iridum 8's plugs and running mobil 4t racing 15w-50 oil & Motul RBF600 brake fluid. Mosfet regulator.

  3. #3
    The "Friends" of Officer Frank Poncherello POWER-TRIPP's Avatar
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    Re: Tuning for lean cruise

    If throttle enrichment is increased, it will account for tip in from a lean condition.

    On your BMW, unless you adjusted the AFR tables at cruise loads, enriching the MAF sensor input does nothing, because the ECU is correcting from Lambda input.
    "To succeed in this game, you have to dabble in the boundary of disaster." -Sterling Moss

    "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!', but 'That's funny…'" Isaac Asimov

    www.POWER-TRIPP.com

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  5. #4
    Menace To Society HarriS's Avatar
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    Re: Tuning for lean cruise

    Quote Originally Posted by Jaket
    I think speedy gets hesitation quite fast when leaned out. when I was using Harri's eco map, I had to richen couple of cruise areas up, because it felt little hesitant to me.
    I also noticed the 1050 does not like very lean mixture for some reason. Injector sizing (too large), injector design (atomization problems with short pulse width), too large intake ports (look huge to me) or something like head design. It simply does not burn lean mixture effectively for some reason. Adding ignition advance compensates to certain point. I think 1050 will not reach 50mpg on cruise with stock parts. 42-45mpg is pretty much all you get at best case. Adding "huge" amounts of ignition advance at low load/throttle input decreased the throttle input from 7-8% to 5-6% at 60mph. This did the single biggest improvement in fuel efficiency on my experiments and significantly improved throttle response. I could not reduce fuel very much before the hesitation began. It runs very rich on light load stock.

    I only tuned the sub 15% trottle input area for economy. Above that it is tuned for max power. 1050 goes faster than is allowed in finland with 15% throttle so that is the reason. If I accelerate or want ot go fast I always use more than 15% throttle. I observed this with the Scangauge.

    Bikes like Hayabusa and gsxr 1000 are very fuel efficient and extremely powerful even at stock tune. on the other hand some like MV agustas drink huge amounts of gas and do not make more power. making an gasoline engine with good part load efficiency is a great achievement and true proof of the design. Anybody can make the peak power if necessary just by copying somebody else if not able to design by own. fine tuning is what makes the difference.

    I tuned the eco map on the edge of hesitation on my bike. Your setup seemed to go over the edge.

  6. #5
    Menace To Society HarriS's Avatar
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    Re: Tuning for lean cruise

    I did a bit of fine tuning and now it seems a bit better. I got true 5.0L/100km (47MPG) at indicated 100km/h by leaning the L tables a little bit below 700mbar manifold pressure. No hesitation and no popping on deceleration so far. Still some work to do but close to the 50MPG seems possible.

    At that speed the throttle position is 5%, manifold pressure 650mbar, O2 voltage still a bit high at about 890-900mV.

  7. #6
    The "Friends" of Officer Frank Poncherello Martin_R's Avatar
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    Re: Tuning for lean cruise

    Are you using the O2 voltage as your tuning reference? I tried the TuneBoy logger again yesterday and it does not seem to give much meaningful data:
    http://i226.photobucket.com/albums/d...uneboy_log.gif

    Looks like the voltage is hovering around 0.875-0.915 pretty much all the time I am on the throttle. Big or small throttle openings. And voltage drops through the floor on all closed throttle deceleration. Other than that, not much happening.

    Only semi-useful piece of info I noticed from the log was that on acceleration from low revs the O2 indicates a lean spike around 23% throttle and ~3000rpm. I guess this is where the ECU is switching from MAP tables to throttle position based.

    Also noticed that once bike is warmed up and idling the O2 voltage violently jumps between lean & rich. I guess the ECU is constantly adjusting back & forth to get a stochiometric average.

  8. #7
    Chicken Strips bierdo's Avatar
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    Re: Tuning for lean cruise

    Yep noticed the violent jumping around when idling too. Not too sure if this is a good thing seems to make the idle jump around a bit as well, lean, rich, lean, rich...
    Think I'll load my current tune back in this evening and turn off the bloody thing? Can't see how it's helping things.

    Also noticed with the F_L switch if you hit F6 when you open up your map (or mine any way) the first two cells go from (from memory gen1 Kehin) from around 980rpm to 3790rpm and are in the 20's going from 980 to zero at about 6000rpm. The modified maps we have, have more cells and rpm range than between these two "stock" settings.

    bikes:

    2007 1050 S3
    2006 KTM 625 SMC

  9. #8
    Menace To Society HarriS's Avatar
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    Re: Tuning for lean cruise

    Quote Originally Posted by bierdo
    Yep noticed the violent jumping around when idling too. Not too sure if this is a good thing seems to make the idle jump around a bit as well, lean, rich, lean, rich...
    That is how the closed loop works. The voltage jumps up and down while the ecu keeps the mixture ~stoich. It is ok and just how it is supposed to be.

  10. #9
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    Re: Tuning for lean cruise

    Quote Originally Posted by Martin_R
    Are you using the O2 voltage as your tuning reference?
    I have the Scangauge II OBD scanner / trip computer semi-permanently mounted on the dashboard. When tuning the steady cruise I use values like throttle position, manifold absolute pressure (MAP), TPS value and corrected momentary fuel consumption on the display in real time. The narrow band O2 sensor voltage naturally is no fancy wideband but gives you an idea if it is lean or rich. On the dyno I use wideband with logging.

    Stock and aftermarket maps for 1050 S3 run pig rich on low load. That may be the reason people are fouling the plugs all the time. By looking at the Sprint and Tiger maps you get an idea how touring maps are like. I like to tune the sub 120km/h area (ie sub 15% throttle) area for best possible fuel economy. I have noticed that when I just slightly "power up" I use at least 25% throttle so 15% and under is just for puttering along the road.

  11. #10
    Menace To Society HarriS's Avatar
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    Re: Tuning for lean cruise

    Cleaned couple of hiccups (lean spots) of the tune and now it looks quite good. I just did a 300km (one tankfull) tour with my wife on her bike and the true and corrected values (with scangauge, not the bike's trip computer) at steady speed on level ground are:

    at 80km/h: 4,5-4,6L/100km (~52MPG)
    at 90km/h: 4,7-4,8L/100km (~50MPG)
    at 100km/h:5-5,1L/100km (~47MPG)
    at 110km/h:5,3L/100km (~44MPG)

    Average for the whole trip was 4,9L/100km (48MPG) with true average speed of 90km/h including 100km of twisties with quite of bit more speed and 200km of dull roads.

 

 
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