Loading effects on AFRs

GNDriven

Active Member
I have been thinking about some data logs I took of some runs on a back street near my house. The first log is were I did a nice linear roll into the throttle ion second gear. The tires hooked decently and I ran it up to about 6500rpm before shifting into third and letting out.
In viewing the FAST data log I noticed the AFRs diverging from the injector duty cycle like < (as suspected). The injector duty cycle went to %86 and the AFRs went to 10.81, which is good. The second run I tried to start in 1st and of course the tires spun and kept spinning pretty much until I shifted into third. This time the AFRs diverge from the injector duty cycle like <; however, the AFRs never went below 11.5. I could see the injector duty cycle was lower than the first pass throughout as well. I am trying to wrap my understanding around how does the computer detect load and adjust for it? How does load affect the AFRs? Thanks
 

turbobitt

Well-Known Member
I have been thinking about some data logs I took of some runs on a back street near my house. The first log is were I did a nice linear roll into the throttle ion second gear. The tires hooked decently and I ran it up to about 6500rpm before shifting into third and letting out.
In viewing the FAST data log I noticed the AFRs diverging from the injector duty cycle like < (as suspected). The injector duty cycle went to %86 and the AFRs went to 10.81, which is good. The second run I tried to start in 1st and of course the tires spun and kept spinning pretty much until I shifted into third. This time the AFRs diverge from the injector duty cycle like <; however, the AFRs never went below 11.5. I could see the injector duty cycle was lower than the first pass throughout as well. I am trying to wrap my understanding around how does the computer detect load and adjust for it? How does load affect the AFRs? Thanks

It detects load by the map sensor. It will run in a different area of the 3D map at different loads. Its really that simple.
AG.
 
Last edited:

delcowizzid

newzealand turbo 3.8
and if you dont have any settings for each gear fueling do all your WOT fuel tuning in the highest gear possible same with spark if you dont have in gear spark adjustments
 

GNDriven

Active Member
It detects load by the map sensor. It will run in a different area of the 3D map at different loads. Its really that simple.
AG.

ok but the psi reading of the MAP sensor was the same for both runs. Which direction should the intake pressure move in regards to load?
 

turbobitt

Well-Known Member
If the map and rpm are the same on each, the load is the same. the difference you may be seeing is the transient response of the system. In other words if it moves slowly through the RPM range in one run and than quickly on another, it is possible that the delay in the O2 sensor reading, logging rate, and AE fuel burn-off can come into play.
AG.
 

bison

Moderator
Staff member
It's also possible the scaling can cause the computer to battle the ve table based on the load. For example the rpm and map spacing on x and y are too far apart so the load can change more while the bubble is only moving in one or two cells. The AE will also be contributing and the rate at which the rpm changes will be different even though the map and rpm appears about the same


BPE2013@hotmail.com
 

GNDriven

Active Member
If the map and rpm are the same on each, the load is the same. the difference you may be seeing is the transient response of the system. In other words if it moves slowly through the RPM range in one run and than quickly on another, it is possible that the delay in the O2 sensor reading, logging rate, and AE fuel burn-off can come into play.
AG.
I have closed loop disabled. So no corrections are being made. I would think the duty cycle is leading the WB at the response time of the WB. AE could be affecting things when the tires were spinning, but I would think it would only increase the duty cycle in the second pass, where the tires were spinning. Doesn't AE add offset to the injectors only if the rate of change of the TPS is high?

I am thinking about the combustion process and how load affects it. For example, does load change the thermal efficiency of the combustion? Does load affect the chemical conversion of oxygen to carbon dioxide and other chemical compounds?

I should prob back up and ask if anyone knows if engine load and AFRs are inversely proportional?
 

delcowizzid

newzealand turbo 3.8
i tune mostly map or as you guys call the SD based tunes with ecu's with no fueling changes per gear.boost a/f ratios in each gear is different even though boost remains constant more air flows under more load but the wastegate allways caps boost at a constant set psi so boost is the same load is different.
 
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