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Metalhead
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I have an AEM-AFR gage on my 2013 sled that tells the amount of air/fuel ratio (oxygen) passing through the exhaust. There is a very distinct lean spot at 5300~6300 rpms where the AFR reads 16~17.5 depending on throttle position. It is "Emissions", the engine is running lean and not enough load in your throttle position to excite the sensors to start to add more fuel.

You will find from 5000~6300 and at 7200~7550 there is a lean spot where the throttle feels "empty".

When you have an increased load on at those same engine speeds, the "empty" feeling will go away.
 

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It's almost always from either clutching (not enough load on engine) or a aftermarket silencer. To narrow it down, click down 1-2 clicker positions and see if it goes away or becomes less frequent. If this helps, add pin weight to run no more than 7900 on clicker 3-4.

Try stock silencer (if running aftermarket) and see if it goes away.
 

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Install Dynamo Joe's clutch kit and the problem disappears and your sled will perform drastically better.

Sent from my iPhone using Tapatalk
 

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Metalhead
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I can't believe how accurate, quick and responsive the AFR gage is. I should have put one on 2 years ago when my buddy FASTZAP told me to when i was diagnosing a 2012 800etec.

I can also prove how accurate it works because i put a fuel controller on with 2 x piggyback injectors on that squirt fuel separately in front of the throttle bodies.

Ive gone through each engine speed range of 1000 rpms and cleaned up my engine and can get the sucker to run at 12.4. Heck, i even had full throttle at an AFR reading of 11 and I had to manually lean the fuel down to get 12.4.

I pull my injectors off and use a borescope - my pistons are beautiful.

The AFR gage is a blessing - you will know exactly what your engine is getting for fuel/oxygen ratio.

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Do a little procedure to rule out a low fuel pressure problem.

The engine must have 43psi at 2000 rpms. When you stab the throttle if the fuel pressure drops low for a moment before it can catch up, the engine will gurgle or bog before engine speed will increase.

When lean at full throttle you will instantly lose engine speed like 1500 rpms from 8000 down to 6500, that is a big bog.

When lean at part throttle like maintaining 7700 then increase throttle and engine bogs to 7000, that is a lean bog - AFR shows it.

I've changed filters on 2 x 2012 sleds this season. One a 600 and one an 800 and both of them had black gukk in the primary filter.

Takes literally 5 minutes to change and costs about $10 bux. Its a regular filter that can be got from any automotive supplier.

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My sled does this and I'm running djs kit & djs ramps. Pin weight is set perfect on clicker 3. Happens 5-6 times a day. I started noticing it the end of last year and it has gotten more frequent this year.
I had this issue at the end of last season and checked the things that was mentioned above but it still did it. actually got worse & worse,

I run DJs clutch kit and A Cooker Thing, and at the time had a Diamond S light weight hood with my own intake design. so I put the stock can back on, nope -- then stock hood and intake back on, nope -- checked all clutching, nope, my point being is that is was none of the above things.

Took it to the dealer and they found multiple temp sensor errors, they replaced both sensors and the module & it fixed the problem. I was happy it was still under warranty
 

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Fuel filter change guys, where's it located? I have a '12 and would like to change it.

Wouldn't you know it, the shop manual I bought is missing the "FUEL" section.
 

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I had this issue at the end of last season and checked the things that was mentioned above but it still did it. actually got worse & worse,

I run DJs clutch kit and A Cooker Thing, and at the time had a Diamond S light weight hood with my own intake design. so I put the stock can back on, nope -- then stock hood and intake back on, nope -- checked all clutching, nope, my point being is that is was none of the above things.

Took it to the dealer and they found multiple temp sensor errors, they replaced both sensors and the module & it fixed the problem. I was happy it was still under warranty
Did your check engine light ever come on?
 

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I use a 1 1/4 inch diameter hole saw. It gives me just enough wiggle room to re-install the heat shield without too much trouble. The best position would be closest to the engine while still being in the center section or belly. But the advantage of having the sensor in the inside bend is having the cleanest location. Tough to find on some tuned pipes especially the 800 ETEC with such a long header and a diffuser that finds itself in a sharp bend. On the SDI 600 and 1000 alike this bend is progressive and lends it self to a number of easy location to choose from. I chose the end of the diffuser which is still in the bend and close enough to the center section for best readings without disturbing the sound waves.
 

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Unfortunately Koso only provides the location of the bung for a 4S. The correct location has been well established in the two stroke community for decades. You can call any tuned pipe manufacturer and verify this information, and it doesn't need to be limited to sleds. Two strokes scooters will do just fine.

The problem with DooTalk is only a small number of owners out of a complete forum have showed that an air/fuel gauge actually works on two strokes. Those are not odds in our favor for the best location. We have the chance to get it right before it sticks on DooTalk.

Update April 21st, 2020

Joey Strub wrote an article about a/f ratios and EGT many years ago that I have found most useful. With certain engines like the E-TEC you can expect the wot values to be even higher/leaner than what is mentioned, but these engines have a knock sensor.

Performance shops that own a dyno like Bikeman, Jaws Performance, Dave Trygstad and many others, they all know these things as they measure them on the sleds they dyno. They also measure backpressure which is critical when designing tuned pipes and mufflers. With the 850 Turbo, BRP shows the correct section of the tuned pipe to take the pipe pressure which is similar for the Wideband.

For the most part I use a Wideband and EGTs to get values from well working stock sleds that have proven to survive for thousands of miles. I use those as my benchmark. This way I don't need to worry about what is supposed to be safe and what is not, nor do I need to worry what is the actual a/f ratio in the combustion vs what is shown on the Wideband. For example a Wideband on an SDI and E-TEC at part throttle will show higher/leaner than stoic (14.7) , but I know for a fact that it is lower/richer in the combustion because if it were lean than it would not pass emissions on a 2S. There are documents available that explain this concept that I don't have handy, but that is obviously how I figured it out.

There is very little on DooTalk regarding a/f ratios, but as you see from one of the members on this thread that it isn't difficult to figure out. You just need to install one and start taking measurements. I need to send a very strong caution on the position of the gauge. When you first start reading the measurements it becomes too easy to glue your eyes on the gauge and not look ahead. Only a short glance can be afforded the same as looking at the rpm gauge. The best/safest location for a Wideband gauge is the highest point possible above the gauge panel.

The very best way to monitor the A/F measurements is to point a video camera at the gauge. I have a data recorder on my AEM Wideband, but the values are all over the place. The readings displayed on the gauge are an average and they are surprisingly easy to follow. This is one reason why a video recording can be more useful than a datalog. Another benefit is having the recording showing rpm, speed and EGT if equipped.

For the most part I just go down the trail at a steady pace and take the readings at different rpm. For example I will look at 4K, 5K, 6K, 7K and 8K rpm. Load comes into play, but generally I am mostly concerned with values that fall in the ball park. Add the EGTs and that's when things get even more interesting as the values at part throttle get remarkably hot. You can go a step further and measure the EGT of the center pipe and muffler. The shop manuals for the SDI and E-TEC supply the overheat temperature of the muffler and you can dig into the E15 research papers to confirm what temperature is considered an overheat. From memory a muffler that reaches 800C is beginning to burn the internals, so the muffler needs to remain a lot lower.

It's the same concept with plug reading. The caveat with plug readings on an E-TEC is that they are difficult to access on the side of the trail, but it can be done. There are times that I care to check the plugs, but I use a Wideband and EGTs to keep this kind of work to a minimum. Imagine going down the trail at wot for so many seconds to get a good plug reading. In under 10 seconds I am reaching some scary speeds, and all this time I have no clue of the A/F ratio until I check the plugs and that is plenty of time to blow-up the engine. When I am working on someone else's sled this is especially a dumb risk to take on an engine that will cost me $3,000 to rebuild. This is multiple times more expensive than a used engine in a car that will likely outlast the car. To me taking such risks is like playing poker will my hard earned money. I have much better chances of winning with a Wideband and EGTs even if I don't know the perfect value to shoot for.

The EGTs offer a very interesting perspective on a 2S sled. Other than the obvious overheat, the main thing that I look for is a balance between the pto and mag side. There is what I call cross flow contamination that happens in the Y-pipe. What I am concerned with is the heat from one cylinder that can effect the other. In 2019 I came across an interesting video from Mazda for their most sophisticated and highest compression 4S that explained the importance of the length of the exhaust manifold to prevent the heat from one cylinder to affect another. All they did to address this issues was to make them longer before they merged into the shared pipe. On a high powered 2S sled that runs extremely lean in the midrange like the E-TEC, it becomes increasingly important that both cylinders are running relatively even.

Without super gauges, the EGTs in the y-pipe offer a unique perspective to the combustion of each cylinder. If they are 30-50F apart, that is one thing. But if they are 100-200F apart then there is likely a problem with an injector not firing right. A Wideband will show the average between the cylinder, while the EGTs in the y-pipe will show the values of each individual cylinder.

The two most important measurements that I use are: 1. In the ball park, and 2. In the left field. A well running sled with 5,000 miles on the engine is solid benchmark. Of course if the measurements are taken on the first rides after the opening of the season, then those values could be skewed from issues developed during storage like injector fouling and old gas.

Fuel Tuning

AFR vs EGT
By Joey Strub

Air Fuel Ratio (AFR) is the ratio of Air (Oxygen) to Fuel (Gasoline). 14.7 units of Oxygen to 1 unit of Gasoline is whats called the Gasoline Stoichiometric ratio. Often AFR is displayed as a digital number, for instance 12.6 on a digit display would refer to only the units of Air. So 12.6 really means 12.6 to 1. Now that you understand what AFR is now lets go over what the different ...values of AFR really mean. At 14.7 AFR all fuel has chemically reacted with all oxygen that was available. At 14.7 there no fuel or oxygen remaining. This is an important number because if the number is higher than 14.7 (Lean) there is too much air and if it is high enough it will not fire at all because the flash from each fuel molecule will not flash far enough to contact the next fuel molecule so energy will be unable to pass from one to the next and the chain reaction can not occur, this is called a Lean Misfire.

Another concern for AFR values 14.7 and over is that there is no unburned fuel to carry heat out of the cylinder. Heat can be very dangerous for engine life. In contrary when values are lower than 14.7 (Rich) there is fuel remaining after flash has happened. This extra fuel has 2 main effects. The first is the engine will run cooler the richer it is because the unburned fuel will absorb heat inside the cylinder and carry out into the exhaust. The second is that the flash will occur at a slower rate because the extra fuel molecules mixed in with the flashable fuel molecules acts like an obstacle that that flash must travel around to get to the next flashable fuel molecule. The Lower the AFR value (Richer) the slower the flash will occur. It is possible to have too many unflashable fuel molecules to for the flash to reach the next molecule, this creates a Rich Misfire. Like anything there is optimal value for AFR depending on application. Major factors that affect optimal AFR is engine type, compression, operating temperature, Octane, Ignition Timing and fuel delivery method.

Exhaust Gas Temperature (EGT) is a measurement of the temperature of the exhaust gas as its entering the exhaust system usually 6-8 inches down stream from the piston skirt if possible. Often EGT is displayed as temperature either in Fahrenheit or Celsius. Exhaust temperature is an excellent bit of information for the serious 2 Stroke tuner since you have a digital number to reference how your engine is running. In most cases the lower the EGT value is the richer/cooler the engine is running and visa versa. So you can adjust fueling to hit your desired EGT at Wide Open Throttle (WOT). Note it is quite normal have a higher safe value for Partial Throttle (sometimes 75 to 150 degrees F) since you do not have the volume of heat needed to cause damage where as that same value may be unacceptable at WOT.

Typical Wide Open Throttle (WOT) AFR Values for optimum power-
* Some engines safe values are outside of typical limits*

2 Stroke naturally aspirated Target AFR/EGT
AFR = 12:0-12.6:1
EGT = 1100-1200F

4 Stroke naturally aspirated target AFR
AFR = 12.8-13.4:1

4 Stroke Boosted target AFR
The more Cylinder Pressure the lower the number!
The lower the Octane the Lower the number!
AFR = 10.9-12.5:1

Where to install EGT bungs 2 stroke exhaust-
EGT Probe should be 6-8 inches from the piston skirt down exhaust stream, If a Y-Pipe joins the exhaust stream in this range install the EGT Probe at the closest point where you could install a hose clamp around each side as close to where the 2 join into 1.

Where to install AFR bungs 2 stroke exhaust-
For best reading without disturbing sound waves AFR bung should be installed as close to towards the engine while still in the belly portion of the pipe, this is the section where the pipe is at its largest diameter. You want to place the bung on the upper half so the sensor will not be upside down when installed (this would cause premature sensor failure).

Where to install AFR bungs 4 stroke exhaust-
Pre-muffler so it will not get inaccurate readings from reversion air pulses, If running a straight pipe 12 inches upstream of outlet should suffice. You want to place the bung on the upper half so the sensor will not be upside down when installed (this would cause premature sensor failure).

Written by Joey Strub
Bikeman Performance Plus

I wrote this to help with a basic understanding of the hows and whys. This is only scratching the surface and I claim no responsibility for any damage that results from inexperience.
 
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