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Discussion Starter #1
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?
 

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2001 5S "Turbo"
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lean burn

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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Re: lean burn

Willie Williford said:
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.

Also see:


Forced Lean Burn
http://www.insightcentral.net/forum/vie ... php?t=4601

Suddenly warmer weather = Holy LB, Batman!
http://www.insightcentral.net/forum/vie ... php?t=4537

Lean Burn clarify
http://www.insightcentral.net/forum/vie ... php?t=2945

Unlimited Lean Burn?
http://www.insightcentral.net/forum/vie ... php?t=3115

Is the holy grail of 'lean burn' an illusion?
http://www.insightcentral.net/forum/viewtopic.php?t=186

HTH! :)
 

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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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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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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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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 :!: :shock: :p

HTH! :)
 

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Discussion Starter #9
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.
 

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NoPetrol said:
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.

HTH! :)
 

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It took me several months to reliably develop the technique to up my mileage. I'm not sure exactly what changed as I would hit it sometimes and not others, but it could be that I developed an unconscious feel for it. Being in WPB, would make that especially difficult if you are travelling on the freeway with all that traffic. It's pretty hilly on my commute and I can regularly get mid 80's and even low 90's on occasion if the conditions are just right (summer time only though). In the winter it's considerably less.
If you are running the A/C, that would have a major effect on lean burn.
It's almost like a Michelob commercial..."some days are better than others".
Wind has quite an effect also, and it's usually windy down there isn't it?
Good luck,
robert
 

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Hmm, my situation is similar to the OP's here. THe highest MPG my car seems to muster out is 75MPG @ 50 MPH (i drive slow). However, there is a leak between the 2 cats on my car. That probably makes a big difference considering hte Air/FUel ratio sensor is pretty close to the leak. After fixing that this weekend then we'll see if lean-burn mode will be activated!
 

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I'd like to input my leanburn mpg, if I am really getting into it

02 Insight, 5 spd, 170k miles. No wind, 80*F weather, Flat Road, non-oem tires at 45psi. (Full Battery charge), A/C off. (ideal Conditions), driving alone (my weight 140lb), Half Gas tank

Can maintain:
90mpg at 45mph
85mpg at 50mph
80mpg at 55mph
75mpg at 58mph
65mpg at 65mph
 

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If you want to know ABSOLUTELY when you are in lean burn, buy a scanguage, and program the Xgauge for it. It will tell you if you are in lean burn, as well as lots of other useful info. I highly recommend this device, and personally rely on it at all times. It even gives you "check engine" codes, and even lets you reset (turn off) them.

Beyond that, I have learned (using my scangauge) that you have to coax it into leanburn. Get up to cruising speed (best if it is warm out, car is warmed up, light or no wind, flatish road, A/C off, heat off or in econ, etc.) Back off the throttle about a third. If you have a scanguage, you can watch your throttle input sensor (TPS). When you get to a TPS down to 17 or better 16, you should "pop" into leanburn. At this point your speed is slightly decreased, your mpg just jumped 25, and you will need to very lightly throttle up to maintain speed. You should be able to maintain for a couple minutes, until the exhaust system will need to purge for a few seconds during which your power will increase and your mpg will drop to normal (down 25). Then you should jump back into leanburn after the purge. If you don't after a few seconds (due to cool weather, cool engine, slight hill, wind, too high speed,... etc.) you may need to back off the throttle again to coax it into leanburn again.

As I said, I am sure this is MUCH easier to do with the TPS and Leanburn guages displayed with a Scangauge, since you can see exactly where you are at, and what is going on at all times. However, you can certainly do this without relying on you experience and "feeling", just a bit more difficult.

Like others have said, the OEM tires at 40plus psi will help.

Hope this helps, if I'm not clear enough let me know.
 

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What an absolutely great thread for folks like me who have only put a couple hundred miles on their new 1st gen and are wondering what the heck that little car is doing.
"Nox Purge"... that explains it! Ha Ha I thought I had a problem but not at all.
(I know this is a 4 yr old thread ... doesn't matter I'm elated after reading it).
In fact I determined today that I could potentially get 80mpg at 58mph on a flat road, no wind, 75deg. The car has impressed me today! My little CRX HF is gonna start collecting dust lol.
 
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