I would think the opposite, which the OP noted. Yes, thinner air requires less fuel to achieve the same AFR. However, less air and less fuel means less energy. It takes the same amount of energy to move the bike at lower elevation as it does at higher elevation. Since you're producing less energy at higher elevation, you'd have to open the throttle more to increase energy output to match the lower elevation. That would result in less mileage.

 

It's like this. I will base it on carb units with the assumption that narrow band 02 sensors are pretty useless at making the corrections. First of all the 1000 foot difference in altitude will make some difference, but damn hard to see it. I base this on flight experience. It usually starts to show around 3000' and up. As you go up the air thins but throttle position is increased to make the same power. The result is a richer mixture. This is because the engine creates vacume to suck air within it's intake time frame. It can't get the normal volume of air because it's thin, but the vacume will still draw the fuel in, or as in injected the throttle position will dictate it. With the thinner air the cooling effect is less. The rich mixture may not cool enough to make up for the thinner air. It may actually run hotter. If the humdity is high the whole thing gets worse as humidity in the air takes up room in the volume and you have less of the good stuff to burn fuel. High humidy also sucks for cooling, big time. Same thing with hot air and cold. Hot= thin , Cold = thick. That's why your engines will go like hell on those crisp dry nights and why it's doggy on the hot humid ones.
Ron

 

My experience has always been that my fuel efficiency improves, sometimes dramatically, with elevation. On the plains of Kansas my Ultra would run around 40mpg at an average cruise speed of 65mph. If I ran 55mph, the fuel efficiency would increase to maybe 45mpg. All of that on the plains of Kansas which run about 700-1000 ft above sea level. In the Rocky Mountains, running over 5000 feet most of the time, and averaging 55 mph, the fuel efficiency would run in the 55-60mpg...significantly improved. The other item of note it is would automatically idle at very low RPM in the mountains too. Then back on the plains the idle was back up to 1000 and the fuel efficiency back down to 45.

 

Well, I'll plead guilty, I guess. I do try to be knowledgeable about things I talk about before I talk about them. And I do try to come across that way. Not necessarily superior, though. You are correct that that perception is an unintended result. I'll see what I can do about it.

Mostly I just try to be helpful whenever I can.

This is a general request: if you think I'm being unfriendly in any way, please give me the benefit of the doubt. If that doesn't satisfy you, ask me to clarify. I'll promptly remove all doubt one way or the other, okay?

Thanks for the heads-up.

 

For that example it's because the PC-III is adding 20% fuel there.

But you see, it does follow the ECUs changes. Since we know already that the added fuel value in that cell is a result of a 120% multiplication, the injector would remain open 8 × 1.20 = 9.6 milliseconds. Exactly following the ECU's changes. Well, not exactly, rather proportionately. The change should be correct.

I can't speak for the DFO, it may simply add time instead of percentage of time.

 

Not many people really know it all like I do. I'm a legend in my own mind!

 

Obviously a greater volume of air will need to be pumped through the engine to achieve the same amount of power, but the ECU takes that into consideration and still only adds enough fuel to get the job done. For that aspect I think it would be mostly a wash.

Maybe the reason fuel economy gets better in practice at higher elevations is that the air is easier to split, to make a hole in for the bike to pass through?

 

Ok, I'll buy that but what I base my idea on is that the HD ecm incorporates all sensors while the PCIII only uses throttle position and rpm to add or remove fuel and cannot adjust for altitude. I would love to hear what Doc has to say on this, I know he can give a much better explanation than I can, when he explained it to me it made perfect sense.

 

Great. You got it. Now this post is heading in the right direction.....

 

........... Jeezus... I leave for a couple of days and it's almost to fisticuffs......

All I am gonna say is that all parties play nice.....

And I believe that the question was posted to ".... the experts..."

That is kinda narrow scope, and can only think of a few of them... Doc1 has already chimed in...

If any more heated exchanges happen, I'll lock the thread.....

If it goes out to other threads, I'll ask the Admins for banishment of the offensive parties...

Capisce?