Is there a way that I can tell when my car is in lean burn? How do I encourage it to enter into this mode? I'm only able to get about 75 miles per gallon going at a constant speed of 55 miles per hour, does this mean lean burn is not coming on?
Normally "lean burn" takes place between 2,000 and 2,500 rpm. in 3rd, 4th,5th gear.
There are other factors involved also. Mainly the "load" on the engine.
Watch your FCD bar. At the speed you are running and the above indicated rpm, and if the "bar" suddenly goes to around 100 mpg without you moving the accelerator pedal you are in "lean burn". Lean Burn happens for seconds at a time, not in multi minutes.
Hope this helps.
Willie
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01 5 speed. "Little Red Rocket"
The first "TURBOCHARGED" Hybrid, (01/2003)
296,000 mi. @ 58.0 LMPG
2007 Honda Fit, Red Sport AT
1998 Ford F-150, NASCAR "Limited Edition"
(3K made, possibly the prototype one)
Lean Burn happens for seconds at a time, not in multi minutes.
Actually "lean-burn" can be sustained almost indefinitely depending on the conditions you described Willie. (mainly engine load) The lean burn "window" will narrow and close with increasing speed. 72 MPHish is the top and VERY hard to maintain. [edit] 72 MPH being the VTEC transition RPM in 5th gear that will make lean burn impossible (the intake valve opening pattern changes)[end edit] 45-55 MPH is much easier. And there is that "pesky" NOx purge that will temporarily enrich the mixture and also cause lean burn to drop out.
When you go into lean burn, you will see the mpg bar going way up and you will start slowing down (all of this at the same throttle position). You will have to increase throttle to stay at the same speed. This lowers the mpg but it's still 25+ mpg higher than you were before lean burn. When the car purges, you will see the mpg bar go down and a burst of acceleration (again, with no change in throttle).
Another good way to tell is that in normal driving, assist will usually begin just under 50 mpg in 5th. In lean burn, assist begins at 70-75 mpg.
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-2000 NF Red
-64.6 LMPG
-JVC El Kameleon HU, JVC 12 disc changer, Infinity Kappa 3-ways up front and Alpine 2-ways in the rear
There are no gauranteed numbers, but if someone averages in the 80 to 90 MPG rsnge for a round trip, you can assume they spent most of it in lean burn mode. Small details like having extra air in the tires make a big difference.
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Kip Munro
The laws of physics don't need changing, but rather our attitude and values. 72.8 LMPG
Lean burn offers 100+ mpg regardless of traveling 55 or 65 mph but the engine can only stay in this mode while the power demand is low. Push the gas to hard and the bar graph will fall as the engine returns to normal operation to meet the increased power demand. The slower speed however allows you to maintain leanburn for a longer period of time because of the lower overall power demand on the engine. As a result the lower speed will produce a higher overall average mpg value.
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Rick 00 #4738 (5sp) Lmpg 90.7 @ 150K miles
02 #1784 (CVT) Lmpg 52.6 @ 35K miles
As Kip stated MPG is not guaranteed. However since you've set a limit on one major factor (speed) then all you have left to deal with is temperature, traffic, and terrain.
And Rick Reece has summarized the concept quite succinctly.
Mild weather (no wind) and temps in the low 70's (min), no traffic either pushing you faster or requiring stop and go, and minimal elevation change can easily yield trip average MPG's in the upper 80's to low 90's under these conditions. Remember that this _also_ requires the OEM tires be installed and inflated to at least the maximum safe rating, 44psi. And _nothing_ else be "wrong" with the car that can effect its MPG potential, e.g. wheel alignment etc.
You'll _also_ have to learn the lean-burn driving technique. Watch the MPG gauge and learn the proper gas pedal response to keep the MPG's in the lean burn range. This generally requires "rollercoastering" the hills (letting speed vary 5-10 MPH) to maintain MPG. And you'll have to learn the NOx purge "recovery" technique too. If your not watching for it you can easily drop out of the lean-burn window too long and your MPG will suffer.
But don't forget to look-up from time to time and make sure your still driving between the ditches
You people are saying I should be getting 100 mpg at a constant 55 mph? It seems, then, that I have never been in lean burn. At a constant speed of 65 mph I can barely keep 75mpg. I've tried just accelerating to the speed I want to stay at and staying there, and accelerating beyond that speed and slowly dropping back. It doesn't seem to be working.
I'm driving in South Florida (90 degrees plus) with no air conditioning with tires inflated slightly beyond the recommended level. I don't get why I'm still barely getting a higher miles per gallon than I got in my old CVT.
You people are saying I should be getting 100 mpg at a constant 55 mph?
I didn't say that at all, but it does require _technique_.
Begin by finding that 75 MPG point then slightly back-off further on the gas pedal without loosing speed. It takes a VERY little touch to maintain maximum lean-burn MPG and speed too. Heavier pedal pressure merely reduces MPG. With this technique you _will_ see the MPG gauge peak above 100 MPG _at times_. The system "computers" also have "learned" parameters and it will take a few 10's of miles for it to become "happiest" (maximum MPG) with your new driving style
You don't note whether or not you've still got the OEM tires and what pressures your running.
Beyond that the problem finding gets a bit tougher. Salt corrosion of the brake slip pins causing brake drag etc.
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Lean Burn
(mainly engine load) The lean burn "window" will narrow and close with increasing speed. 72 MPHish is the top and VERY hard to maintain. [edit] 72 MPH being the VTEC transition RPM in 5th gear that will make lean burn impossible (the intake valve opening pattern changes)[end edit] 45-55 MPH is much easier. And there is that "pesky" 
etc.
