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4-Stroke EFI Basics for Snowmobiles: Part 3

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4-Stroke EFI Sensors

By: Kent Lester

Here’s a list of the most important sensors used in common fuel injection systems and what they do. We’ve noted specifics about snowmobile applications:

* Throttle Position Sensor

The TPS monitors the throttle valve or “butterfly” position within the throttle body. This position actually determines how much air is being introduced into the cylinders. The ECU takes this info, considers the RPM level of the engine, processes the data and regulates the fuel flow accordingly.

It makes sense this data is in constant flux as your thumb moves the throttle randomly during acceleration and deceleration.

* Engine Speed Sensor

The ESS calculates the true speed or RPM the engine is operating at. It works in tandem with the Throttle position Sensor but the TPS reports up-to-date as your thumb presses down on the throttle while the Engine Speed Sensor is already reading the data present in the engine.

The calculation of where the engine RPM is at versus what the Throttle Position Sensor is demanding is the difference. Adjustments are made instantaneously.

* Coolant Temperature Sensor

This one is especially important during start-up and idle when precise fuel flow is critical to fire the cylinders and keep a cold engine running smoothly.

It reports the current operating temperature of the engine and makes adjustments to the fuel flow through the injectors so the engine doesn’t behave “cold blooded” or reject throttle inputs on cold days.

* Manifold Absolute Pressure Sensor

The MAP sensor measures the air pressure or vacuum in the intake manifold as the engine is running.

Manifold vacuum is a good indicator of what level the engine is producing power. Low vacuum means there’s lots of air flow, high pressure means less flow – kind of like the amount of water you can squirt through a garden hose versus a fire hose.

This is an after- the- fact measure of power and verifies with the CPU whether its inputs have been accurate. The CPU then makes further adjustments according to is data map.

* Mass Air Flow Sensor

The MAS sensor calculates how much air is entering the engine. It’s a very precise temperature reader and its guts are designed to measure temperature changes on the intake side many times per second as the engine is running. More air flow has a cooling effect and less air means a higher temperature is present.

When the ECU receives this info it responds by either lengthening or shortening the time the injector stays open. Although common in automobiles, in powersports applications like snowmobiles a Manifold Absolute Pressure sensor is used instead of a Mass Air Flow sensor.

* Oxygen Sensor

This one is located within the exhaust pipe or the exhaust manifold and monitors the amount of oxygen present in the exhaust after combustion is completed.

This helps the ECU determine how rich or lean the fuel mixture is after it’s been burned. If a lot of oxygen is present it can mean the engine is too lean; not much oxygen and it’s rich and probably not meeting emissions standards.

Oxygen sensors are critical tools in the regulation of exhaust emissions. Although EFI managed 4-strokes burn very, very clean, even without an exhaust oxygen sensor, most current 4-stroke snowmobiles use the more costly closed loop system (oxygen sensors in use) because 02 sensors are deemed to be necessary at this point in emissions regulation history.

The term “open loop” merely means the EFI system does not use an oxygen sensor.

Keep checking back for more on this 4-part series about the basics if Snowmobile EFI technology.

Fuel Mileage Controversey

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Question:

I e-mailed your staff last year concerning the claimed 20 mpg of the “06” Yamaha 4 cylinder sleds. Nobody I ride with has ever gotten that kind of mileage and the dealers even say 15 mpg is what to expect.

I know there is a process to reprogram the electronics on the sled through the instrument cluster and have been told by a Yamaha technician how to do it. Unfortunately I did not write down all the info but have gotten some info over the Totally Yamaha web site. This changes the co calibration point of the sled and effects the low and mid range of the fuel delivery system.

I was wondering if you have any info regarding this and if you could pass it along to me. I know you are supposed to use exhaust gas analyzers to be the most accurate but was told you can try various settings as long as you keep the base data to enable you to go back to original if need be.

Any help to get the mileage up would be appreciated,

Thanks.

Gary Schoppenhorst

Response:

I find it interesting that with the number of Apex and Attak 1000’s sold last year you are actually the only person I’ve received a comment on regarding poor mileage. I’ve had many questions about suspension and front end stuff but not mileage.

I’m not questioning your numbers – I’m sure you’re getting what you say you are. However, we did not experience this with our PR unit Apex last year. In fact, we put huge miles on the sled and found it to be consistent – providing the snow was packed – in its mileage numbers.

I know there are chat rooms with people claiming poor mileage but I have to wonder just how wide spread this problem was. For sure fiddling with your ECU is not a good idea; particularly if you’re chasing a leaner burn in the interest of mileage.

If you can achieve 15 mpg then I wonder how hard it would be to get 20 – depending on your riding conditions – by altering your throttle habits?

Let me make this point. Did we ever get low mileage out of our Apex 1000? Yes. However it was always when we were on the loud handle – running big lakes at or near the C-note for long pulls. Under those circumstances we would never expect good mileage.

The same goes for the other sleds which we have seen 20 plus mpg from. The 600 SDI and 1000 SDI Ski-Doo’s go way down in MPG on full throttle pulls. So does the Vector. MPG is a difficult thing to quantify.

You don’t have to ride like an old lady to get good mileage #’s but you do have to tame it down a bit.

Motorhead Mark

Do Fan Cooled Motors Lose Power After Warm-Up?

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Question:

I have a 550 Fan cooled Polaris; I read in another magazine that fan cooled motors lose some of their power after they warm up.

I know liquid motors run cooler and make more power. Is this a big problem for the fan cooled motors? Should I be concerned about it? What can I do to help the motor?

Thank you for your time.

Mike Rohwedder

Response:

Fan cooled engines do not lose power when they get up to operating temperature – they’re designed to make their claimed HP at temperatures experienced under normal operating conditions.

Any 2 or 4 stroke engine, liquid or fan cooled will suffer from decreased power when temperatures go outside of the engine’s design limits. Example: If you operate a liquid cooled sled and do not have adequate snow on the coolers in the tunnel it will ultimately overheat, loose power and seize.

If you operate a fan cooled with the hood vents blocked or under huge loads on a 50 degree F day, it will over-heat, loose power and seize.

In actual fact, fan cooled engines are less likely to have severe overheating problems as they do not rely on snow to cool them.

Fan coolers use air (always present – albeit it can become too warm) and fuel – (always present and always relatively cool). Fuel is a very important and reliable part of the cooling system for a fan cooled engine.

This is why a fan cooled engine is generally not as efficient as a liquid cooled motor – the fuel is performing two jobs – cooling and energy for combustion.

The reason you have heard this story relates to this reality. When you increase specific output in a given displacement engine it will produce more heat. Example – a fan cooled 550cc mill will deliver about 60 ponies.

If you port and time the same 550cc displacement mill to produce 100 HP – easily attainable – the engine must be liquid cooled to live. Get it?

Your 60 HP motor cannot be hurt or improved with extra cooling – provided you are operating it within its design parameters.

Enjoy it and don’t worry about cooling.

Motorhead Mark

Tourism Eastern Townships Welcomes Snowmobilers

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Press Release –

Come and celebrate with us the cradle of snowmobiling in the Eastern Townships!

Tourism Eastern Townships, in collaboration with Tourism Québec, would like to draw your attention to the snowmobile attractions in the Valcourt area.

2007 will be an important year for Valcourt, where the snowmobile was invented and developed by Joseph Armand Bombardier.

A century after the famous inventor’s birth, the Bombardier Snowmobile Museum will be entirely renewed.

The Grand Prix ski-doo de Valcourt, from February 16-18, celebrates its 25th edition with exciting competitions.

The Bombardier plant has a new production line using the latest technology. New 2008 models will also be on display.

Also note the 2,000 kms of snowmobile trails to be explored in the Eastern Townships!

For more information call 1-800-355-5755 and visit EasternTownships.org

4-Stroke EFI Basics for Snowmobiles: Part 2

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EFI Thinks for Itself

By: Kent Lester

By introducing electronics and computer controls, automotive engineers have been able to eliminate the problems carburetors have been wrestling with for years.

For instance, with EFI, no choke system is necessary and the fuel and air flow balance is always consistent despite weather conditions or the temperature of the engine. Fuel flow is near perfect on every stroke of the engine and fuel is not wasted as it “puddles” in a manifold waiting for a valve to open so it can enter a combustion chamber.

The result is an engine that starts easier, idles with precision and accelerates at any RPM level without hesitation. Is the exhaust cleaner? In most cases it is.

How does it work? Back to the aerosol sprayer mentioned in Part 1. If your finger could press and release the nozzle hundreds of times per second and time the pulses so they fall exactly at a pre-determined point, you’d be doing what EFI does.

In order for this precision pulsing to take place, an EFI system has to be able to “read” several conditions. This is accomplished by using a team of electronic sensors located on or within the engine and exhaust system.

The data accumulated from these sensors is channeled to a “brain” or Engine Control Unit (ECU) where the information is processed and the decision as to how long the injector should stay open is made and how much fuel should be squirted in relation to the air flow available.

The ECU also controls engine timing so the injectors are squirting at the engine’s optimum time window to maximize fuel efficiency and power depending on its load.

The Engine Control Unit (ECU) controlling a snowmobile’s EFI system is really a computer that processes the feedback it receives from a fleet of electronic sensors and then chooses the duration and frequency of the pulses the fuel injectors should be spraying gas.

This tiny “black box” is well hidden within the snowmobile’s wiring network and protected from the elements.

Like any computer it contains programs or “maps” that process data and apply it as required. These data maps are created by the manufacturer and are programmed into its complex database.

They detail every possible scenario of outdoor and internal engine temperature, fuel flow, air flow, existing power, load demand and every other conceivable possibility at every RPM. These calculations and adjustments are processed thousands of times per second.

Keep checking back for more on this 4-part series about the basics if Snowmobile EFI technology.

4-Stroke EFI Feedback

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Written by: Jonathan Belanger

I just read Part 1 of the Electronic Fuel Management article with great interest. I found the article well written. There was, however, some omitted information.

First off, the MAP sensor is used in conjunction with an air temperature sensor to determine the density of the air charge within the manifold. It is this information that adjusts the fuel delivery for things like altitude and temperature.

Additionally, there is another style of EFI system that was not presented. This type of system uses a titanium wire in an air flow housing placed before the throttle body. This replaces the combination of MAP and Air Temp sensors.

The wire is electrically heated and when air passes through the sensor, the volume and temperature of the air charge is determine.

This system is better at adjusting for altitude and temperature and meters the air flow much better than the MAP/Air Temp sensor combination.

In the mid-80s Ford introduced the V8 Mustang with the MAP/Air Temp Sensor combination and switched to the Air Flow Sensor a year or two later.

Follow Up:

Jonathan:

Fascinating information, thanks so much for sending it. The article we posted is a fairly elementary one targeted at introducing snowmobilers to the various electronic controls being used specifically on sleds today.

There are three more follow-up segments to this article that will be coming out on the web in the next few days and then another whole series on 2-stroke electronics that will be posted after the December issue of Supertrax is out. Some of the missing info you mentioned may be mentioned in the other segments.

I’d never heard of the titanium wire system you wrote about and would love to learn more about it. Please send me a link if you have any more info.

Kent Lester

’07 Phazer: 2-Stroke Weight, 4-Stroke Great!

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’07 Phazer: 2-Stroke Weight, 4-Stroke Great!

When you first sit on a Phazer you’ll notice feedback strangely similar to a YZF motocrosser. The narrow and tall seat delivers a dominating feel looking over the trail and puts the rider in the perfect position for a stand up ride similar to the YZF.

The deep tunnel and low hung running boards let you pinch the mid-section of the seat with your knees and pull the Phazer around in deep powder when playing off the trail.

The front section of the Phazer has more Vector and Apex influence with the use of injection molded body panels popping outward, mirroring the shape of the engine and driveline components they cover. This makes the Phazer look more concept than production and really catches your attention.

The boiler underneath this little steam cannon is a 2-cylinder 500cc liquid cooled, fuel injected 4-stroker. The mill is based on the single cylinder YZF250 motor and they strapped two of those 250s together to make a stump pulling torque monster of an engine fueled by a 43mm Keihin dual throat EFI throttle body.

This sophisticated engine uses an Apex-like remote primary drive to drop crank revs from near-12,000 RPM to 8,000 RPM at full whack, thus ensuring belt reliability.

The power characteristics of the Genesis 80hp mill are similar to other Yamaha 4-strokes: they make potent power down low. The torque generated by this 499cc reactor is incredible and propels the Phazer up to cruising speed quickly.

The Phazer creates what could be called the best, stock factory exhaust note, period. This little gruntmeister barks horsepower commands to the 14-wide by 121 inch track and lets you know it’s bred from the same line of engines strapped into the YZF MXers.

Squeeze the go stick and an angry 4-stroke thump reverberates out the rear exiting exhaust and plays a tune sweet enough to win American Idol.

The all new Phazer-specific Pro-Active rear suspension delivers a plush ride in the harshest conditions. Using a Polaris-like double coupled drop link and an Arctic Cat-ish Torque Sensing Link on the rear arm plus what appears very similar to Ski-Doo’s SC-4 accelerated front arm shock set-up, Yamaha has melded the best ideas in the biz here placing a full 16.1 inches (at the rear axle) of whoop-whipping travel at your beckoned call.

The dual A-arm front suspension is equally as competent, using a small spaghetti-like sway bar similar to that on an MXZ 440 Ski-Doo snocrosser. The bar attaches to the lower A-arm via forged dog bones and effectively counters front end roll under hard cornering conditions.

Holding the A-arms to the skis are a sweet set of extruded aluminum spindles, hollowed out to the max, looking more like an aftermarket part than a production piece.

When it comes to choosing between the GT or FX package the most significant difference is in the suspension department. The rear end of the GT comes with two Kayaba IFP gas shocks.

The front arm shock has a threaded preload adjuster allowing for an even wider range of adjustability versus a snail cam collar found on many competitive sleds.

Out back, square torsion springs can be adjusted to one of three preload settings. The front end of the GT uses two aluminum KYB shocks with threaded bodies. The adjustability of a threaded body provides for preload is a huge benefit over snail cam collar adjusters found on most low cost snowmobiles these days.

We predict the biggest problem Yamaha will face is consumer perception of this new generation snowmobile. To combat this, Yamaha has geared up promotions that include a set of Phazers on a trailer with matching jackets and helmets for a ridiculously low monthly payment. Smart.

Slammed FreeStyle

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Question:

The cool looking freestyle chassis drag sled in your latest issue really caught my eye.

Where can I find the details on the sled? It looks pretty cool slammed to the ground.

Todd Olson

Response:

The Freestyle shown in the November issue is a mod sled raced by Craig Marchbank. Craig says the lightweight of the chassis appealed to him and it just seemed like a natural to make it into a drag sled. I’m sorry, I don’t know what he used for power in this cool looking rig.

CJ Ramstad

4-Stroke EFI Basics for Snowmobiles: Part 1

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Carbs: Better or Worse?

By: Kent Lester

To understand the efficiencies of 4-stroke EFI you first need to understand the inefficiencies of carburetors.

Think of an aerosol spray can. Whether you’re spraying paint or hair spray, press the nozzle down and you’ll get a consistent, unending (until the can is empty) spritz of liquid.Carburetors work something like that.

When the engine is running, because of the vacuum or sucking effect of air flowing into the carburetor, gasoline is being sprayed as long as your thumb is holding the throttle open.

Every stroke or revolution of the engine whether intake, compression, firing or exhaust, the carburetor is delivering fuel. Although the cylinder’s intake valves regulate whether or not the gas is actually getting into the combustion chamber there’s always a range between the ideal amount of fuel and too much fuel being available.

The presence of too much fuel not only causes those annoying burbles and hesitations when you tip-in the throttle but can cause an idling engine to stall or can make start-up difficult and flooding too easy.

Air flow is another issue. Oxygen is your engine’s second fuel and if the balance between air and gasoline is off, the engine can find itself in a “too rich” environment where performance is affected or a “too lean” situation where excess heat is generated and the engine’s physical health is in jeopardy.

To get a cold engine started, carburetors depend on a “choke” or an “enrichener” to adjust the balance between fuel and air flow. Gradually, more air is introduced as the engine warms up.

Various manual, mechanical and electric choke devices have been added to carbs over the years with varying results. Certainly, with snowmobiles, the manually operated choke is most common.

Keep checking back for more on this 4-part series about the basics if Snowmobile EFI technology.

Sneak Peek Rumors: Package Speaks Volumes

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Despite the fact all the snowmobile manufacturers are tense about releasing info surrounding early release limited build models, we received a 50 pound invitation to Ski-Doo’s annual “Sneak Peek” 2008 model preview in January.

The 50 pound package included two 25 pound bar-bell weights and a small white envelope.

The always intuitive minds here immediately got the point.

The ad showing a Ski-Doo pilot adding bar bell weights to his REV parked next to a Yamaha 4-stroke is in the most recent issue of Supertrax.

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    SNOWTRAX has established itself as the most watched snowmobile TV series in North America.
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