Fuel Trims VS AFR

[ed_GST]

Just wondering ... since when i had my other car i tuned looking for the 11.0 to 11.5 AFR

But here on DSM's is all about Fuel Trims

How is the AFR related to the 0% on my fuel trims?

Are'nt stock AFR @ WOT very rich ???

If i try to get a leaner AFR will the ECU try to correct it back ???



BTW i did searched ... nothing showed up

 

[Gstclipse69]

You do tune for 11-11.5 at wot.

When you are tuning via fuel trims you are at light/moderate acceleration. The ecu is in closed loop and relys on fuel trims for the correct maps.

When your fuel trims are close to 100% your afr should be about 14-15 cruising. This is stoich.

When you go wot the ecu is in open loop, going by values you set in the high throttle table. (of a safc) A stock car will have a very rich wot afr of 9.5:1. I suppose this is for safety reasons.

 

[ed_GST]

thanks for the info

so basicly the fuel trims are tuned only for closed loop
for remapping with bigger injectors after that just tune WOT

 

[jshuman]

I will try to clear that up for you. The two things you are referring to, afr and fuel trims, are both used in the tuning process. To start at the beginning, lets define both of those terms.

1. AFR. This is the air-fuel ratio. It is a measure of the amout of oxygen in relation to fuel. This value will vary in different modes of opperation. In closed loop operation (cruise and idle operation), the AFR will hover around 14.7:1, which is the stoichiometric ratio for oxygen and fuel. In open loop operation (wide open throttle) the AFR will decrease from the stoichiometric ratio to one as rich as 10:1 depending on the setup.

2. Fuel trims. In short, a fuel trim is fuel that is either being added or taken away. You will usually see this represented in the form of a percentage. In closed loop operation, the goal of the ecu is to keep the AFR at stoich. The fuel delivered to the combustion chamber is determined by the amount of air seen my the mas or maf. However, the ecu used data from the 02 sensor to determine the AFR. If the ecu determines that it needs more or less fuel to achieve this desired AFR, it corrects via fuel trims.

Usually when it comes to tuning, you will see fuel trim calibration mentioned before AFR. You calibrate idle and cruise conditions using fuel trims. Then you adjust AFR to tune wide open throttle conditions.

I hope that helps you out,
Justin

 

[jshuman]

Ha you beat me to it. No one had replied when I started typing.... I am slow .

 

[ed_GST]

Usually when it comes to tuning, you will see fuel trim calibration mentioned before AFR. You calibrate idle and cruise conditions using fuel trims. Then you adjust AFR to tune wide open throttle conditions.

I hope that helps you out,
Justin

thats was enough hehe

thanks

hope that helps everyone else