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.