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Old 03-19-2014, 09:06 PM   #1 (permalink)
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Civic HX Lean Burn Monitoring via ScanGauge (Video + Info)

The goal of this thread is to provide information to Civic HX owners about monitoring lean-burn via the ScanGauge. While the SG won't calculate an accurate MPG number like the MPGuino for our HX's, it does provide critical info that the MPGuinio does not provide, which is the main reason I chose to use one instead of buying an MPGuino.

How to Program Lean Burn Gauge to ScanGauge II

Brucepick details how to program the XGauge in this post.

What Do the Readings Indicate?

From my observations:

0 on the gauge = no fuel (it happens when in DFCO)
2-35 = lean burn. It isn't on/off. The computer adjusts the ratio based on load. Lighter load = leaner mixture.
60-80 = Normal mixture 14.7:1. 76 is usually where it stays at when not in lean burn.
80-100 = Heavy acceleration
125 = startup mixture (~12:1 maybe even richer)

It's also interesting that when my engine is idling, the LB gauge reads 1-3. So we can assume at idle the car will enter lean burn.

I believe that the number the SG displays is a voltage reading. 0 = 0V, 125 = 1.25V. This article about the LAF sensor and this article about sensor troubleshooting tell me that the voltage between max lean and max rich should be at least 1 volt on a good sensor, so 1.25 volts seems reasonable. Note that actually measuring voltages on the pins of the sensor will not get these readings because the readings are based on reference voltages, not ground. Also, the sensor is not comparing the oxygen content to outside air. It compares it to the diffusion chamber oxygen, which the ECU controls. The articles also state that the HX and VX could run up to a 23:1 a/f ratio in lean burn mode. So we can assume that near 0 is the highest ratio (23:1).

Conditions for Lean Burn on the HX

Many people have tried to explain the conditions required to activate lean burn on the HX and VX. From what I can tell the HX and VX are very similar, if not the same. I have been in lean burn in all gears except 1st, and at speeds around 70 mph and as low as 25 mph.

The biggest factor is engine load. Lean burn only activates under light load. For me anything above 60-70% can kick it out of lean burn.

The other big factor seems to be intake temperature. Coolant temperature is not a big concern. I have entered lean burn before the car was fully warm, when the coolant was 125 degrees. As long as it is in closed loop operation, it will go into lean burn under the right conditions. But intake temp is another story. The colder it is, the harder it is for me to activate lean burn and stay in it. On warm days I can drive all 50 miles to work and never leave lean burn. On cold winter days sometimes it doesn't want to enter lean burn.

RPMs have been discussed in previous posts, but I do not think it's a big factor. I have a VX transmission which puts me below 2000 RPM at 50 mph, almost 1500 RPM. I can still enter lean burn. Of course any high RPMS like 3000 would not engage lean burn due to a switchover to 16 valve mode.

Some people have reported not being able to enter lean burn after exiting for 2 mins, or a certain amount of miles. I have no problems with that. I can go to high load and kick out of lean burn, and as soon as my load returns it goes back into lean burn.

Video Demonstration

I shot this video on cold night home from work. It demonstrates the different readings for different load conditions. Remember, low load = lean burn. The captions in the video explain what is going on.

http://youtu.be/r9GDerlnzOQ


Something to Add?

I am far from an expert on this subject so if you have anything to add post it below! I am interested to see if anyone else has this setup and if it behaves differently.

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Old 03-19-2014, 11:42 PM   #2 (permalink)
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My UltraGauge does the same thing.
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Old 03-20-2014, 02:53 AM   #3 (permalink)
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Quote:
Originally Posted by iveyjh View Post
My UltraGauge does the same thing.
Is it the same readout of 0-125? The SG also has codes to enter that are listed as A/F Ratio Sensor 1 Bank 1, but when I enter those in no data shows up. Honda must not display that data, which is a shame because the actual A/F ratio readout would be more helpful than just the voltage.

Do you have similar experiences with lean burn conditions? I was a little worried at first because I have a cheap(er) O2 sensor. It game me codes and trouble until I figured out my non-OEM exhaust manifold was the problem. Switched back to an OEM setup and LB started working again, codes gone. The only thing now is that my EGR valve is broken. I actually have the connector disconnected from the EGR valve, so another interesting FYI, the LB works without EGR.
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Old 05-02-2014, 12:17 AM   #4 (permalink)
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this is strange, i tried this on my mom's Acura TL and at ~50mph under light loads the LBN drops to mid 10s. Go above 50mph and the LBN jumps back to 70-80s. So honda v6 is a lean burn too?
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Old 05-02-2014, 04:59 PM   #5 (permalink)
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Many current Honda engines use lean burn, especially outside the US. Lean burn is not limited to the 5th and 6th gen Civics. For the 7th generation Civic both the HX and EX engines are lean burn, despite the EX being the more powerful trim. The EX engine is the same in almost every way to the HX engine, with minor ECU and gearing differences that account for the difference in horsepower and fuel economy. Both engines use a VTEC-E system just like on the HX and VX of earlier generations. During low load, low RPM driving one intake valve is closed and air/fuel mixtures are leaned out. When VTEC activates it switches to a normal cam profile using all 16 valves for more power. The EX has a more aggressive cam profile than the HX, allowing greater horsepower.

Beyond the 7th generation Honda developed i-VTEC which combines all the features of all the previous VTEC versions, including VTEC-E. In i-VTEC engines the ECU can control valve timing and lift, allowing some i-VTEC engines to run in 12 valve mode and achieve lean air/fuel ratios. It's important to note that i-VTEC dramatically reduces pumping losses experienced at low load, low RPM operation. This alone increases fuel economy compared to a normal engine.

I'm not sure if the TL or other i-VTEC motors have a lean burn mode, but I know the technology exists in some i-VTEC motors like the 1.3 i-VTEC. VTEC-E has not gone away, it's just implemented in a different way.
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Old 05-04-2014, 12:27 AM   #6 (permalink)
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Quote:
Originally Posted by cbaber View Post
Many current Honda engines use lean burn, especially outside the US. Lean burn is not limited to the 5th and 6th gen Civics. For the 7th generation Civic both the HX and EX engines are lean burn, despite the EX being the more powerful trim. The EX engine is the same in almost every way to the HX engine, with minor ECU and gearing differences that account for the difference in horsepower and fuel economy. Both engines use a VTEC-E system just like on the HX and VX of earlier generations. During low load, low RPM driving one intake valve is closed and air/fuel mixtures are leaned out. When VTEC activates it switches to a normal cam profile using all 16 valves for more power. The EX has a more aggressive cam profile than the HX, allowing greater horsepower.

Beyond the 7th generation Honda developed i-VTEC which combines all the features of all the previous VTEC versions, including VTEC-E. In i-VTEC engines the ECU can control valve timing and lift, allowing some i-VTEC engines to run in 12 valve mode and achieve lean air/fuel ratios. It's important to note that i-VTEC dramatically reduces pumping losses experienced at low load, low RPM operation. This alone increases fuel economy compared to a normal engine.

I'm not sure if the TL or other i-VTEC motors have a lean burn mode, but I know the technology exists in some i-VTEC motors like the 1.3 i-VTEC. VTEC-E has not gone away, it's just implemented in a different way.

The particular TL i'm talking about is a 2003 model. It's just a VTEC system, you can actually hear the crossover at 4500rpm. below 4500rpm it seems to always be operating low lift cams. Again experimenting with the LBN gauge, i have only seemed to be able to get really low values like 15s at 50mph cruising only.
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Old 05-04-2014, 09:25 AM   #7 (permalink)
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Quote:
Originally Posted by cbaber View Post
Is it the same readout of 0-125? The SG also has codes to enter that are listed as A/F Ratio Sensor 1 Bank 1, but when I enter those in no data shows up. Honda must not display that data, which is a shame because the actual A/F ratio readout would be more helpful than just the voltage.

Do you have similar experiences with lean burn conditions? I was a little worried at first because I have a cheap(er) O2 sensor. It game me codes and trouble until I figured out my non-OEM exhaust manifold was the problem. Switched back to an OEM setup and LB started working again, codes gone. The only thing now is that my EGR valve is broken. I actually have the connector disconnected from the EGR valve, so another interesting FYI, the LB works without EGR.
On the UltraGauge it will read from 0.00 to 1.25 so just multiply 100X and you get the ScanGauge readings
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Old 06-27-2014, 01:29 PM   #8 (permalink)
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My issue is that I'll hit 3 lbn 50s lod but it still shows low 30s or high 20s. What mpg should it be showing? 1997 hx
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Old 06-27-2014, 05:31 PM   #9 (permalink)
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I got a p0420 on my way to work. I think that May be my issue with the poor mpg.
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Old 06-27-2014, 09:20 PM   #10 (permalink)
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I got a p0420 on my way to work. I think that May be my issue with the poor mpg.
Maybe. If the honeycomb melted and is clogging the pathway, it sure could impact your mileage. If all it is, is a substrate material which has been "used up", it should have only a minimal impact on MPG. Downstream O2 sensors barely factor into your fuel trims. If you only got p0420 today, I doubt the computer is correcting anything enough to affect MPG.

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