Ultragauge DFCO observations
 

I have had erratic results from tanks in which I used DFCO extensively, so I reset my displays to allow me to observe both the instant FE reading and the primary O2 sensor. The FE readings are, of course, a calculation by the UG, while the Primary O2 reading is the voltage coming from a dedicated sensor. The sensor reading would have to be a better indicator of DFCO than the UG calculation.

Results: the UG will read 999.99 mpg almost anytime you have it in gear and release the throttle but the O2 sensor often will still indicate fuel being burned. This is sometimes quite a lot of fuel, it would seem. In third gear descending a hill for 10 seconds with a thoroughly warmed engine, the UG showed 999.99 instant MPG while the O2 readings was .6 volts, slowly sliding down to 0.135 volts and then 0.015 volts. Very lean... but not "cut off" ...

Why do you feel the sensor reading is a better indicator?

Does the .015 reading indicate fuel passing through, or fuel still left in the line?

Because the ultragauge is dependent on the sensors and there is no FE sensor. So therefore the 999.99 mpg number is a UG calculated guess. The sensor is directly reading the exhaust and reporting out voltage according to what it finds. Given how many times the engine turns in a second at 1500 or 2000 rpms, I can't imagine residual fuel would last more than 1 or 2 seconds. But this can go on continually over 10 seconds, and not at 0.015, but at numbers like 0.6 and such. There's no way that at a 0.6 O2 voltage reading from the sensor the FE could actually be 999.99 mpg, is there? What do you think?

I don't know. I'm not sure how that works, but am curious.

Me too.

I always coast in gear rather than in neutral because my Camry has DFCO. My UltraGauge reads 999.9 MPG when I release the throttle.

I can say for myself that it does save gasoline, I just averaged over 37 MPG on my last trip cycle from lots of in gear coasting and other techniques in my Camry :) I hope this helps!

-SC

o2 sensor & lean burn
 

According to the manual:

The lower the O2 sensor voltage, the more lean the car is. I saw a graph at one point but can't remember where I saw it. 0.600-0.855 is normal range though.

[Edit]: I don't have experience with DFCO as I can't get my UG to detect when my insight is in DFCO, and I highly doubt the insight doesn't have it.

There's a good explanation here, the best air to fuel (atf) ratio for economy being 16:1, which they say is the target for closed loop operation.

http://www.endtuning.com/images/airfuel.jpg

There it is. That's the graph I was talking about.

So based on the above chart, would it make sense to keep track of these gauges on the UltraGauge to help increase fuel economy??


-Percent Engine Load
-Intake Manifold Absolute Pressure (MAP) PSI
-Ignition Timing Advance
-Intake Air Temperature (°F)
-Absolute Throttle Position Percentage
-Bank 1 Oxygen Sensor 2 Voltage
-Bank 1 Wide Oxygen Sensor 1 lambda Voltage
-Volumetric Efficiency
-Mass Air Flow 2, Calibrated/Calculated

The following are similar, so it's a matter of experimentation and to see which ones are most useful to you. I use % engine load or MAP for acceleration, and instantaneous mpg or (maybe) an o2 sensor for coasting. I personally didn't care for the throttle position sensor, perhaps as the pedal doesn't attenuate very well.

% engine load
MAP
absolute throttle position
o2 sensor
instantaneous mpg

Definitely calibrate the gauge to work with the various sensors in your car.

I think if you follow all those gauges while driving you're going to crash! ;)

I find that the most useful are engine load and rpm. I follow instant FE readout too, in order to reassure myself things are going well. I started this thread to report how the UG reports DFCO.

A further observation on that point is that the O2 will sometimes need more than 2500 RPMs to go into DFCO, and sometimes not. But generally, i have determined that it will go into DFCO quickly, though often not intantly, once the engine is warm. This explains why I had erratic fuel economy variations between pump and the UG once I started using DFCO in the spring. I was relying on the instant FE reading, and it's not accurate enough. I think the O2 reading is helping me to improve my use of DFCO, which is awesome

I don't understand, what 0.600 reading? I only attempt DFCO in situations where I can coast for a substantial stretch, like 10 seconds or more. I use it for free engine cooling and battery charging. Under DFCO, I'll turn the alt on and blast the cabin fan. The O2 is helping to reveal the conditions under which the ecu will set-up DFCO more easily and quickly so that all, or nearly all, of those seconds are actually true DFCO, instead of just a very lean burn. I would guess 0.600 would be about stoich, no?

I'm not convinced the o2 sensor reading of .6 volts is indicative that Dfco is not working.

Why does instantaneous mpg show that Dfco is almost immediate?

I understand your skepticism, and I believe there is a chance it turns out correct. But it seems unlikely. The UG probably shows 999 because the UG mpg reading is not based on a specific sensor, but is rather a calculation. So when I clicked the button on the UG saying my car has DFCO the unit began showing all those nines whenever I let go of the throttle for a second while in gear. They have programmed the UG to assume that there is not fuel. I don't think they took into account the variations I'm seeing. It'snot a scientific instrument. It's really just a very good consumer toy. So I guess I'm saying my hunch is that I should believe the voltage reading from my relatively new sensor rather than the UG's calculation. Don't forget that once I started using DFCO last spring, after three years of basically accurate calibration of the UG's fuel consumption calc to the gas station pump I use, I suddenly started getting FE data showing a big difference in FE. The UG was suddenly way off. Suddenly it was always telling me I had used a lot less fuel than my regular pump was saying I had. The O2 sensor data I'm seeing is the best explanation of that experience: that the UG's instant FE calc is imprecise for DFCO scenarios and exaggerates my car's effectiveness in cutting off the fuel.

I notice that in my car if I am in top gear above 45 MPH then release the accelerator, DFCO will enable and show 999.9 MPG on the UltraGauge. Once it drops into 3rd gear below 45 MPH then DFCO will disable and will read 100-150 MPG and decrease as the speed drops.

Do the RPMs drop below 1100 when dropping into 3rd gear? If not, you should still be in DFCO.

You may need to fine tune the injector cutoff setting of the Ultraguage if DFCO is not registering correctly. See page 47 of the owners manual.

My page 47 is blank. But on page 37, my copy makes a statement about how the value used to establish DFCO for a given vehicle only "represents a best estimate." They note that each car manufacturer "has their own algorithm for injector cutoff."

It also says that the cut off should only be seen during in gear deceleration, but I and some others--one in this thread--see it sometimes when shifting out of gear and letting the engine decelerate down to idle. Often I'll see 999.99 on the instant FE reading at such times.

I'll know better how my car use of the O2 reading to judge authentic DFCO after a couple tanks. I'll report that in my fuel log, and possibly here too if I remember. :thumbup:

Page 47 is in reference to injector cutoff. Page 37 refers to fuel level.
UltraGauge EM v1.2 user manual (Version 1.2, Purchased on 10/12/12 or later)
http://ultra-gauge.com/ultragauge/su...al_1_14_14.pdf

In my 2001 Toyota Camry, if I am in overdrive at any speed above 45 MPH, then DFCO will activate and show 999.9 MPG until it downshifts into 3rd gear and decreases below 1,400 RPMs. After that, it will read 75-100 MPG, depending on terrain and weather conditions.

Also, I noticed that when using cruise control when the computer forces my car to downshift to maintain the constant speed, during the downshift, my UltraGauge will read 999.9 MPG and cause my Average MPG gauge to increase.

This goes against what I've learned about cruise control. Is this normal? Is it really saving fuel???

Once the ultragauge shows DFCO as 0.000 volts on the primary O2 sensor, the reading will stay zeroed-out in second gear until the car hits idle speed and needs gasoline to keep from stalling.

Could it be a leaky fuel injector? When you hit DFCO your injectors are at zero duty cycle and you should almost immediately see your AFR's peg out full lean.