Here is the story: I've been commuting on my 03 919 for the past 5 months or so. Constantly, I get 50 (give or take one tenth) in MPG. I only ride it between work and home. However, when I filled up the tank yesterday, I noticed the MPG dropped to 46.5. I am really puzzled. The only things that have changed during the past week were: colder temperature (low 40's) in the morning and I bumped up the tire pressure to 36 psi. Everything else was pretty much unchanged. Could this be something like dirty air filter?
I've heard it has something to do with the gas formulation during the Winter (or colder) months. I drove over to New Orleans a few years ago during Christmas time, and I averaged 13-15mpg in my Tacoma. Even though my Taco is lifted, I was surprised. I was then told that the gas formulation in the Winter is different, resulting in poorer mileage. Maybe higher levels of Ethanol?
thye do change formulation of the fuels we get for the winter, but, normally the more dense air compensates for that - Did you switch gas stations ? Ive noticed i constantly get better milage with Exxon vs. BP for some strange reason - Ive been able to duplicate it over several tanks in both my bikes and truck.
Its always work checking your air filter, its amazing how crappy those things get ! Ive also niticed that In my truck, my milage drops as it gets closer to oil change time - stange , but, about 3500 miles I loose 1 or 2 mpg , this has been constant since 4.5k miles and my truck now has 65k on it.
Air density. When the air is colder, the molecules are closer together. You are then sucking in more air at colder temps. The vehicles computer compensates with more fuel. Making gas mileage a little poopier. Ever notice how your bike makes more power when it's cold out? Yep.
I forgot to mention also that the air/fuel mix runs richer until it's up to optimum. It takes a while for the engine to really hit this temp when it's pretty cold out. Speaking of optimum temps... try turning a wheel by hand when it's cold compared to when it's, say, 80 degrees out. It's harder.
Seeing about a 10% drop in MPG is about average. You're right in that realm.
I noticed my temp gauge is running cooler and I know the puter thinks it needs to squirt a lil richer mixture. I finally saw my lil fuel warning light blink at me yesterday. 178 miles and put 3.75 gallons back in. 50 mpg any way you look at it.
Ever notice how your bike makes more power when it's cold out? Yep.
This is definitely true with gas turbines (jet engines). I work for a company in San Diego that manufactures turbines rated for 2,000 to 20,000 hp. We adjust our hp rating depending on site conditions, usually an ISO standard 59, 80 or 120 degrees F. Horsepower can vary anywhere from 100 to 1,000 hp depending on the conditions.
Think of how stupid the average person is, and realize half of them are stupider than that. - George Carlin
Stupid question but how does the ECU know to squirt more fuel? I thought the ECU only knows about RPM and throttle position. Are you guys saying there is a temperature sensor or an 02 sensor telling the ECU about air density?
No. What they are saying is, an already over rich setting is getting matched by the cooler air density.
The PCIII gets programed to correct the fuel ratio(13.1) to make the most power out of the motor.
Some maps are still a little on the rich side so the cool air is slightly still noticeable.
Those that run on the lean side don't notice much of a difference.
So...to optimize the bikes performance, is to run a winter map, & a summer map. The 919 wouldn't be able to tell the difference in weather or altitude otherwise.
It is fairly common for carbureted bikes to get slightly better mileage in cold weather, at least above 0 degrees C due to the fact that the denser air picks up more fuel when running past the orifices, but the combustion is somewhat more efficient the colder the air charge is and it takes smaller throttle openings to get the same performance. Below 0, the fuel has difficulty atomizing properly, and efficiency drops. Open loop injection systems are not as self correcting as carbs, depending on the map and the amount of reaction to a colder reading from the intake air temperature sensor (which the 919 has mounted in the airbox) which tends to richen things up.
Remember also that cold, denser air is just that -- denser, and therefore creates more resistance as you move through it. I know for a fact that my mileage drops 2 to 3 MPG when I'm wearing my bulkier winter gear as opposed to my much tighter summer leather jacket and gloves, at least above 70 MPH.
If this computer doesn't register and use temp and altitude, then it's a very primitive lil bugger. On an auto(OBD2) when you tune for performance the 1st thing you do is lower the thermostat, so the injectors pump more gas, thinking the motor is cold. The OBD2 actually tunes the car as you drive,hot,cold,rain,mountians, or N.O.La below sea level. I guess the computer we get is: 1-2-3- squirt, 1-2-3- squirt. I want my $$ back!
The original poster said he got worse gas mileage with cold weather. Then some wise listers said the computer squirts more fuel in cold weather and I was asking how does it know to squirt more fuel?
I completely understand better gas mileage and more power in the winter due to denser air, I just did not get how some folks were saying the FI delivers more fuel in the cold. Because as far as I know, the ECU on our bikes is a pretty primitive little bugger.
By the way, OBD-II is just the protocol these guys use to send fault messages and data. On Board Diagnostics I think is the acronym. I wish our ECU supported that protocol, it would be fun to be able to connect to that data stream.
There IS an intake air temp sensor(IAT) & MAP sensor. The CPU knows the air is cold(more dense) & knows the pressure of that cold air. It figures the "total amount" of air & gives more gas to keep the ratios right. MPG goes down a bit.
Also prolonged warm up times & slightly cooler engine temps in the cold drives down MPG. More power is a bonus. The air filter would matter more though. Are you checking that airbox water drain regularly?? Wet air filters or wet portions of them are essentially clogged. BTW, rear tire should be more like 40psi.
My AIT sensor mod from forums about exhaust stink/smell would be very helpful here I think. It will cause a leaner run & in theory more MPG. I've only ran it for one tankful but, the early results are good. I went 178.x miles & it took 3.8xx gallons. With all the decimals points plugged it came out to 47mpg. With maybe about 30 miles being city miles. The smell was reduced significantly also.