Setting the throttle points on an afc.

[BIRDCLAWTSi]

So here it is. Setting the throttle points on an afc, The low throttle is generally set at 30%, And the high 70-80%. It is to my understanding that the ecu is in closed loop operation until wot. So my question is this...Why dont we set the low throttle for 99% and the high for 100%? If the closed loop fuel control is only going to go for target fuel maps during closed loop, Then having the high throttle point come in at 70 or 80% is'nt doing anything anyway. Example: If i were to set my low throttle corrections all a little lean, The ecu would correct the settings i have made and go for target afr's anyway right? And setting the fuel trims to adjust. So technically the only time the settings i have made make any difference is at wot? Does this make sense?

I was just thinking about this. I guess i am just wondering why we dont set the throttle points to transition with closed to open loop fuel control. Sorry if this is a little hard to follow, And any insight would be appreciated. Thanks in advance.
-Dave

 

[steve]

I don't know where you get the impression that the ECU is in closed loop until WOT but it's incorrect. There are other factors besides TPS position used to decide if the ECU can be in closed loop including intake air and engine coolant temp.

Your also forgetting about the reason most people have an SAFC to start with and that is to correct for changed in injectors and MAFs. This means that the low table is mainly the baseline correction for those changes.

The target fuel maps are used during open loop, not closed loop. In closed loop the targets 14.7:1 and uses the narrowband sensor for feedback to manage it.

The SAFC interpolates the corrections from the low and high tables for TPS positions between the low and high setting. Changing the percentage changes how the interpolation effects the resulting correction for an RPM and TPS input.

How much tuning away from the stock maps do you need at low RPM in open loop?
What is the problem your trying to solve?

 

[BIRDCLAWTSi]

I don't know where you get the impression that the ECU is in closed loop until WOT but it's incorrect. There are other factors besides TPS position used to decide if the ECU can be in closed loop including intake air and engine coolant temp.

Your also forgetting about the reason most people have an SAFC to start with and that is to correct for changed in injectors and MAFs. This means that the low table is mainly the baseline correction for those changes.

The target fuel maps are used during open loop, not closed loop. In closed loop the targets 14.7:1 and uses the narrowband sensor for feedback to manage it.

The SAFC interpolates the corrections from the low and high tables for TPS positions between the low and high setting. Changing the percentage changes how the interpolation effects the resulting correction for an RPM and TPS input.

How much tuning away from the stock maps do you need at low RPM in open loop?
What is the problem your trying to solve?

Thanks for the reply, It is not a problem i am trying to correct, It was a thought i had. I do understand how it works for the most part, I was thinking along the lines of where the best transition would be. I have everything dialed in, Fuel trims dead on, afr's are very good. 14.7:1 would be the target map i was refering to in closed loop. I realize that i can throw everything way off in either direction(Rich or lean) in closed loop, But it will try to bring it back to 14.7:1 no matter what, As long as the trims are'nt to far out. I was however under the impression that the high throttle table was primarily for wot, But it will make corrections from 70% on. It was more of a thought i had from a thread i read.

 

[steve]

I was however under the impression that the high throttle table was primarily for wot, But it will make corrections from 70% on.

It is primarily for wot but the TPS points set how the SAFC interpolates between the two tables. Above the high point the SAFC just uses the high table settings and below the low point it just uses the low table. Where the ECU switches from closed to open loop however isn't as simple as just the TPS.

The high table setting are a combination of the corrections needed for changes in the fueling systems and for tuning from the factory open loop fuel maps. Since you don't usually wind up tuning much below where your turbo begins to spool the lower RPM setting on the high table usually are exactly the same as on the low table and the SAFC interpolation doesn't do anything because the setting are identical. Since you can be under boost and not be at 70% throttle the SAFC will use a correction between the two tables and move more to the high table as the throttle opens. You can play with how that works for doing part throttle tuning or just worry about WOT.

 

[BIRDCLAWTSi]

It is primarily for wot but the TPS points set how the SAFC interpolates between the two tables. Above the high point the SAFC just uses the high table settings and below the low point it just uses the low table. Where the ECU switches from closed to open loop however isn't as simple as just the TPS.

The high table setting are a combination of the corrections needed for changes in the fueling systems and for tuning from the factory open loop fuel maps. Since you don't usually wind up tuning much below where your turbo begins to spool the lower RPM setting on the high table usually are exactly the same as on the low table and the SAFC interpolation doesn't do anything because the setting are identical. Since you can be under boost and not be at 70% throttle the SAFC will use a correction between the two tables and move more to the high table as the throttle opens. You can play with how that works for doing part throttle tuning or just worry about WOT.

You hit it on the head with part throttle tuning, That is what i was thinking about, I would think most people don't drive at WOT all the time, But to get the most out of daily driving, Part throttle is key. I did see in the faq's there is a formula to figure the in between interpolation of high and low and tune within the two, The thing i was thinking about is that if your mid range is let's say a little on the rich side, Before you go to the high/wot, And the high/wot is on the lean side, Will there be a jump in the afr's, And maybe not such a smooth transition? I am at the point in tuneing where i am just begining to really understand the effects of the afc on timing and airflow. It is really quite limiting but i am not a rich man.