986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Wideband O2 sensor and piggyback controller

The Radium King · 03-14-2018, 09:22 AM

there's a variety of triggers for the move from open to closed loop - temp, throttle position, rpm. once the ecu decides to move to open loop based on these triggers, then it basically goes by maf reading. realise that the apexi is just a sophisticated, programmable potentiometer. and yes, the process is more complicated than i've stated - the ecu is looking at different maps depending on iat and other variables, but fundamentally, you are just intercepting the maf signal and modifying it. there is a good video on youtube of a guy doing the potentiometer thing on a 996.

the apexi i think also has the ability to intercept/modify other data such as temps so as to impact change-over points, etc., but that is above my pay grade.

in closed loop, the ecu is monitoring products of combustion, so if the apexi intercepts the maf signal and modifies it (with the intent of sending an incorrect airflow reading and impacting fueling) the ecu will see things are out of whack via the o2 sensors and trim to correct. why would you want to modify closed loop regardless - it is already as good as it gets.

presumably if you tweak the maf reading too much (with the apexi or a potentiometer) the closed-loop fuel trims could so high that a cel gets triggered. but note that the cel goes off at about a 30% error (.7 to 1.32, if that is what those readings mean) so if you've modified fueling that much you would be pushing your open loop fueling from 12.5:1 to well past 14:7:1 and be running way too lean anyways.

and i think that is the biggest gut check - how lean do you want to make your open loop operation? you are going to have a baseline of 12.5 or so to 1; do you want to change it to 13:1? 13.5:1? how risky do you feel? presume there is some safety margin in the porsche settings, but how much? how will the leaner afr affect timing? that's why i went with the 996 tune - if you can find a shop with the tool that knows what they are doing then it is a 5 minute job. if they don't then you have to pay to train them and are looking at, in newarts case, 3 hours labour.

03-14-2018, 09:22 AM	#4
The Radium King Registered User Join Date: Apr 2010 Location: Canada Posts: 3,121	there's a variety of triggers for the move from open to closed loop - temp, throttle position, rpm. once the ecu decides to move to open loop based on these triggers, then it basically goes by maf reading. realise that the apexi is just a sophisticated, programmable potentiometer. and yes, the process is more complicated than i've stated - the ecu is looking at different maps depending on iat and other variables, but fundamentally, you are just intercepting the maf signal and modifying it. there is a good video on youtube of a guy doing the potentiometer thing on a 996. the apexi i think also has the ability to intercept/modify other data such as temps so as to impact change-over points, etc., but that is above my pay grade. in closed loop, the ecu is monitoring products of combustion, so if the apexi intercepts the maf signal and modifies it (with the intent of sending an incorrect airflow reading and impacting fueling) the ecu will see things are out of whack via the o2 sensors and trim to correct. why would you want to modify closed loop regardless - it is already as good as it gets. presumably if you tweak the maf reading too much (with the apexi or a potentiometer) the closed-loop fuel trims could so high that a cel gets triggered. but note that the cel goes off at about a 30% error (.7 to 1.32, if that is what those readings mean) so if you've modified fueling that much you would be pushing your open loop fueling from 12.5:1 to well past 14:7:1 and be running way too lean anyways. and i think that is the biggest gut check - how lean do you want to make your open loop operation? you are going to have a baseline of 12.5 or so to 1; do you want to change it to 13:1? 13.5:1? how risky do you feel? presume there is some safety margin in the porsche settings, but how much? how will the leaner afr affect timing? that's why i went with the 996 tune - if you can find a shop with the tool that knows what they are doing then it is a 5 minute job. if they don't then you have to pay to train them and are looking at, in newarts case, 3 hours labour.