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Hey all!

There are some wonderful threads about lean burn conversions, but they all seem to assume the reader have some basic knowledge - I'm hoping to fill those gaps.

  • Which cars came equipped with lean burn ECUs? Was this JDM only, or were MT cars around the world equipped with one?
  • Do lean burn ECUs alternate rich and lean in order to avoid fouling/damaging the catalytic converters?
  • How does the driver of a lean-burn equipped Insight know when they're in lean burn mode?
Thank you!
 

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You can buy a ob2 [email protected] c and it will light up green. The 92 civic vx has lean burn technology .its been around for some time. Long before the insight . You have to be light on the pedal on mostly flat surfaces and the car will feel like its floating.
 

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All of the Gen 1 MT cars can enter lean burn. The Japanese CVTs could also enter lean burn. The American CVTs do not enter lean burn and the consensus is that Honda went for an SULEV emissions rating and a lower compression engine.

There is no indication of when you enter lean burn. The OBD2C&C that @Honda hybrid442 refers to has a green LED which lights up when the car is in lean burn. When I want to know for sure if I've entered lean burn, I use a moderately expensive scan tool by Autel that displays the air fuel ratio from the upstream oxygen sensor. If you drive the car long enough (better if you're using one of these tools) you can learn the technique for coaxing the car into lean burn.

How easily the car drops out of lean burn is another question. My experience has been that if you have an aged oxygen sensor, you'll have trouble keeping it in lean burn if you have to put any kind of load on the engine. If you use the wrong sensor or a cheap sensor, that also can prevent you from using lean burn.
 

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Sorry about that. It appears that that is another thing that the "SITE" has eliminated along with the picture of the G1..
 

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  • Do lean burn ECUs alternate rich and lean in order to avoid fouling/damaging the catalytic converters?
Besides going into and out of lean burn due to needs for more or less power during a typical drive, lean burn will also cycle ON and OFF at steady cruising, such as highway at constant load, called an "NOx purge cycle." My understanding is that the mixture needs to go rich for a short period to prevent build-up of oxides of nitrogen, not sure if that's to prevent catalytic converter degradation/damage, reduce emissions, or both. Probably both.

  • How does the driver of a lean-burn equipped Insight know when they're in lean burn mode?
Besides having an OBDIIC&C, one can generally tell when it's going into or coming out of lean burn by a few things. For example, on the highway, if you're cruising steady, every minute or so there will be a slight surge in power. If you leave the throttle absolutely still you'll gain speed. Moments later, if you haven't given it more gas, you'll feel a slight stumble (from warble to almost imperceptible 'hiccup') and a reduction in power - when lean burn is coming back. If you watch the instantaneous fuel gauge during this 'purge cycle' you'll see bars pulling back during the purge and then increasing when lean burn comes back online.

A similar principle applies to any type of driving, such as in-city, so long as you have a long enough stretch of time to be holding the throttle steady and at low to moderate amounts. Typically one can coax the car into lean burn by accelerating up to speed and pulling back on the throttle just slightly more than you would were you to try to maintain that speed. Basically, overshoot your target speed by a couple MPH and pull off the throttle a bit, and during that pull-off the engine usually goes into lean burn. If you don't come back on throttle too heavy it will stay in lean burn, instantaneous MPG bars will usually be over 50 at minimum, usually more like 60-100, depending on how light you are on the throttle...

Perhaps more or most basically, jumps and drops on the instantaneous fuel MPG gauge, of about 25 MPG or more, correspond to going into and out of lean burn, so long as you're not doing radical things with the throttle.
 

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Typically one can coax the car into lean burn by accelerating up to speed and pulling back on the throttle just slightly more than you would were you to try to maintain that speed. Basically, overshoot your target speed by a couple MPH and pull off the throttle a bit, and during that pull-off the engine usually goes into lean burn. If you don't come back on throttle too heavy it will stay in lean burn, instantaneous MPG bars will usually be over 50 at minimum, usually more like 60-100, depending on how light you are on the throttle...
This is a great description of the technique.

It is very important to not make any sudden movements on the throttle. I believe the ECM looks at the rate of change of the throttle position sensor and if it changes too quickly it drops it out of lean burn expecting you to demand acceleration. Similarly the throttle movements should be very gradual for several seconds before you enter lean burn.

Also, you won't be able to enter lean burn until:
  • you're above 25 MPH (I don't recall exactly the number)
  • above 1500 and below 2500 RPM or so (sweet spot around 2000 RPM)
  • a few other parameters I can't remember (engine temperature?)
While it may be harder to enter lean burn as you approach 1500 RPM it appears to stay in lean burn below this number.

It's been found that it's possible to remain in lean burn while shifting if you don't change the throttle position during the shift (and the resulting RPM is still within the lean burn range). This signifies the importance the ECM places on the throttle position sensor data to determine whether or not the driver is about to demand power from the car. But this obviously can lead to messed up shifts and insults to the transmission.
 

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...I believe the ECM looks at the rate of change of the throttle position sensor and if it changes too quickly it drops it out of lean burn expecting you to demand acceleration.
I don't really get that 'feel' - it feels more like absolute thresholds and/or something based on 'load' and all that. Seems like I can move the throttle fast as much as I want - just as long as those movements don't push the engine load too high - or whatever parameters too high.

Also, I wrote this: "...overshoot your target speed by a couple MPH and pull off the throttle a bit," but actually, I think I let off the throttle entirely, but only for about a second or two. IF you know exactly where the throttle needs to be when coming back on it, I'm pretty sure you can get there as fast as you want without missing lean burn. If, on the other hand, you don't know, then you have to ease into it so you don't overshoot that 'load' juncture, or whatever juncture/threshold...
 

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I don't really get that 'feel' - it feels more like absolute thresholds and/or something based on 'load' and all that. Seems like I can move the throttle fast as much as I want - just as long as those movements don't push the engine load too high - or whatever parameters too high.

Also, I wrote this: "...overshoot your target speed by a couple MPH and pull off the throttle a bit," but actually, I think I let off the throttle entirely, but only for about a second or two. IF you know exactly where the throttle needs to be when coming back on it, I'm pretty sure you can get there as fast as you want without missing lean burn. If, on the other hand, you don't know, then you have to ease into it so you don't overshoot that 'load' juncture, or whatever juncture/threshold...
Actually thank you for correcting me. It's quite possible that once you are in lean burn, the ECU is looking for load being exceeded, and doesn't care much about throttle position. I'll have to give that a try. I guess we're not going to know until we can find one of the engineers to tell us!

On entering lean burn, or even staying in it, I kind of have a feeling that I have to let off the throttle mostly, but not completely. On my car at least, letting off the throttle completely can shut down the injectors. I don't have data to confirm this. Again, wish we really knew more about what the engineers were thinking.
 

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Letting off the the throttle does close down the injectors.
OBDIIC&C Injector pulse width, AFR, Load, TPS etc is all interesting to watch.
 

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  • How does the driver of a lean-burn equipped Insight know when they're in lean burn mode?
You'll have to get a cheap OBDII Bluetooth adapter like this. ($5.79 shipped)
Download the free app torque onto your phone, setup to monitor the o2 sensors.

When the car entered lean burn, the 1x2 o2 goes to 0v.
85716
 

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I suggest everyone buy a ELM OBDII Bluetooth adapter to monitor the status of their Insight if they want to know. It's cheap and easy.

I found with my car, it easiest to enter lean burn around 15% TPS.

Once you're in lean burn, as long as you move the TPS slowly, you can get it up to around 28% TPS without dropping out of lean burn.

85717
 

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  • above 1500 and below 2500 RPM or so (sweet spot around 2000 RPM)
It can go into lean burn outside that range. A key thing is that it will be MUCH more willing to enter and stay in lean burn in 5th gear where the throttle position/load would otherwise kick it out if it were in 4th gear for example.

You may also find you not only can stay in lean burn easier in 3rd or 4th at higher speeds due to the parameters of lower engine load and a lower throttle position/vacuum (whichever it uses), but the gearing may simply be more efficient there than the shift indicator tells you.
 

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Please include your Location in your Profile.
Thank you.
 

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Also, I wrote this: "...overshoot your target speed by a couple MPH and pull off the throttle a bit," but actually, I think I let off the throttle entirely, but only for about a second or two. IF you know exactly where the throttle needs to be when coming back on it, I'm pretty sure you can get there as fast as you want without missing lean burn. If, on the other hand, you don't know, then you have to ease into it so you don't overshoot that 'load' juncture, or whatever juncture/threshold...
Instead of letting the throttle "off a bit", here's how I do it. I let off enough so the FCD bar graph is just above 100 mpg, I then hold that throttle setting for ~1/2 to 1 second and then give the throttle enough gas so the FCD drops to some reading between 75 to 90 mpg and hold the new setting. After a bit the FCD will suddenly go to a very high mpg reading and stay there. If you have an OBDIIc&c will read something like 22.1 AFR before the FCD increases its reading.

If the car won't go into lean burn, repeat the whole sequence. Sometimes the car wants to do a purge first and my OBDIIc&c will show 13.7 AFR. You'll just have to let it finish the purge before you try lean burn again.

My engine will not go into lean burn unless the OBDIIc&c coolant temperature is 154° F or higher.
 
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