Lean burn with negative split timing
07-14-2011, 12:10 AM
#130
One thing that has concerned me in the past WRT these maps is the seemingly excessive degree of precision that Mazda used to calibrate them. This is obscured when represented as Lambda values, but here are the tables represented in decimal.
I don't know how to interpret it, but those are lots of different kinds of "1.0 lambda." I've wondered if they are for per rotor fuel balancing... I have lots of theories, but need more tools to figure it out.
I don't know how to interpret it, but those are lots of different kinds of "1.0 lambda." I've wondered if they are for per rotor fuel balancing... I have lots of theories, but need more tools to figure it out.
07-14-2011, 01:17 AM
#132
"That would be telling."
http://www.youtube.com/watch?v=zalndXdxriI
http://www.youtube.com/watch?v=zalndXdxriI
Last edited by oltmann; 07-14-2011 at 01:21 AM.
07-14-2011, 03:14 AM
#134
3-wheeler
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07-14-2011, 06:38 AM
#136
Originally Posted by Flashwing
Now some real world data!
I have a couple instances of running lean during cruise. Between Gallup and Flagstaff I saw 190 miles for a little over 7 1/2 gallons of gas!
Here is data showing my motor is capable of crusing with AFR's as high as 16.3:1
...
Either way being able to flash back to stock worked out fine. It was cool to see the limits of the motor in terms of lean operation and fuel mileage. Getting nearly 25 mpg out of a rotary motor is pretty impressive in my opinion.
I have a couple instances of running lean during cruise. Between Gallup and Flagstaff I saw 190 miles for a little over 7 1/2 gallons of gas!
Here is data showing my motor is capable of crusing with AFR's as high as 16.3:1
...
Either way being able to flash back to stock worked out fine. It was cool to see the limits of the motor in terms of lean operation and fuel mileage. Getting nearly 25 mpg out of a rotary motor is pretty impressive in my opinion.
07-14-2011, 10:20 AM
#139
Honestly though, I'd love to believe that there is a secret to getting miraculous FE, but most of the reasonably well implemented tests I've found on leaning out an engine not designed for lean burn have shown 0-3% improvement. As usual, there isn't much rotary-specific info, and while there seem to be some believers on RX7 club, nobody is specific about their gains, nor how they tested...
07-14-2011, 02:11 PM
#141
I know better than to fall for your stink bait challenge. If you want to conclude that, in addition to me not knowing anything about the Cobb system, that flying westbound from NYC to LA is the same thing as flying around the globe eastbound because in the end you got to the same place then fine.
I wish you the best on your travels and hope that you finally reach your destination ...
I wish you the best on your travels and hope that you finally reach your destination ...
07-14-2011, 02:51 PM
#142
I tried running .95-.92, at first I got good results, but averaged over a few weeks, same as before. However, apparently I did it wrong - using "closed loop" tables. I don't know what maps to modify. The only way I've found to get the ve table to affect CL AFRs is to over or undershoot the target by 25%. Then I'm only getting feedback control in one direction.
The only fuel map I haven't touched is the injector latency.
The only fuel map I haven't touched is the injector latency.
03-09-2012, 04:31 PM
#145
I know this is thread necropsy, but I have found why the Rx8 won't lean burn. The rear o2 sensor acts as a failsafe and if it detects a mixture lean of stoich during cruise it will drive the mixture back to stoich. I've tested this twice both by feeding the front o2 sensor a offset signal to actually drive the mixture lean, and by feeding the rear o2 sensor an offset signal to show the mixture as being lean. Both times the ECU drove the commanded mixture down until the rear o2 sensor was no longer reading lean.
Here is a data set I collected. I turned on the offset during the middle of the drive and quickly revved the engine to signal the change. I then drove until it had dropped commanded AFR to about 14.4:1 and removed the offset.
Avg commanded AFR before offset: 14.65
After offset: 14.45
Avg rear o2 voltage before offset: .61 volts
Avg rear o2 voltage after offset: .53 volts
I have also tried offsetting in the other direction. It did add to my cruise AFR slightly, but then it had no further effect effect. I imagine that is just the difference between what it expects to see after a CAT and what it actually sees after an empty pipe.
Please note that this only applies when out of idle. The ECU recognizes the idle is supposed to be lean burn and completely ignores the rear o2 sensor.
Edit: Forgot to mention the most important part. With about .2 volts added you can go as lean as you want. The ecu just doesn't want to be hitting the lean limit of the rear o2 sensor repeatedly. The only problem I'm having is a CEL for o2 sensor volts high. I'll either have to reduce my offset or put a zener diode in to limit voltage.
Here is a data set I collected. I turned on the offset during the middle of the drive and quickly revved the engine to signal the change. I then drove until it had dropped commanded AFR to about 14.4:1 and removed the offset.
Avg commanded AFR before offset: 14.65
After offset: 14.45
Avg rear o2 voltage before offset: .61 volts
Avg rear o2 voltage after offset: .53 volts
I have also tried offsetting in the other direction. It did add to my cruise AFR slightly, but then it had no further effect effect. I imagine that is just the difference between what it expects to see after a CAT and what it actually sees after an empty pipe.
Please note that this only applies when out of idle. The ECU recognizes the idle is supposed to be lean burn and completely ignores the rear o2 sensor.
Edit: Forgot to mention the most important part. With about .2 volts added you can go as lean as you want. The ecu just doesn't want to be hitting the lean limit of the rear o2 sensor repeatedly. The only problem I'm having is a CEL for o2 sensor volts high. I'll either have to reduce my offset or put a zener diode in to limit voltage.
Last edited by Harlan; 03-09-2012 at 04:35 PM.
03-09-2012, 10:30 PM
#149
Just started looking at this, but...
There is a switch that sets the rear O2 active for fuel control.
When the switch is "on" it can build a rear O2 fuel trim, and it switches to the fuel targets in the closed loop a/f targets B table.
The subroutine that sets the switch checks for a bunch of conditions... I don't understand all of them, but some of the ones I do get:
Looks for coolant temp over 70C.
Looks for difference between measured and commanded equivalence ratio must be over ~0.099.
It pulls a value from this load/rpm lookup table, and looks for a value equal to or greater than 128.
It is like the closed loop exit determination, so some are hard limits, some increment a counter against a delay threshold. Not sure which is which right now.
Anyhow, it seems to generally looking for cruising conditions and big errors in the wideband reading.
Also worth noting, these are the condition under which it will change the rear o2 fuel trim, if a trim is already set it is always applied to the closed loop target.
There is a switch that sets the rear O2 active for fuel control.
When the switch is "on" it can build a rear O2 fuel trim, and it switches to the fuel targets in the closed loop a/f targets B table.
The subroutine that sets the switch checks for a bunch of conditions... I don't understand all of them, but some of the ones I do get:
Looks for coolant temp over 70C.
Looks for difference between measured and commanded equivalence ratio must be over ~0.099.
It pulls a value from this load/rpm lookup table, and looks for a value equal to or greater than 128.
It is like the closed loop exit determination, so some are hard limits, some increment a counter against a delay threshold. Not sure which is which right now.
Anyhow, it seems to generally looking for cruising conditions and big errors in the wideband reading.
Also worth noting, these are the condition under which it will change the rear o2 fuel trim, if a trim is already set it is always applied to the closed loop target.
03-10-2012, 10:33 AM
#150
Release the twins.
