OK we all know that stoichiometric A/F for gasoline engines is 14.7.

I know that boosted engines need to be run richer, between 12 and 11 A/F ratio. Much of the dyno tuning seems to be in that range. However, the dyno tuning occurs at WOT when the ECU is in open loop. So all of my knowledge is about WOT.

However, I'm rarely at WOT in my daily driving of my MINI. I have a Throttle Position Meter and some trips in my MCS I don't go over 40% throttle. I also invested in a Wideband O2 sensor and need help in understanding if my car is tuned right for part throttle situations.

What's the A/F we should be running when at:

Part throttle with vacuum?
Part throttle with no boost nor vacuum (atmospheric)?
Part throttle with low boost (<10psi)?
Part throttle with hi boost (>10psi)?

 

I found this:

http://www.edelbrock.com/automotive/eps_sect1.html

This should relate to a fuel injected system as it does with a carborated system, right?

 

When Josh at Unichip did my custom...on the road tune..... he spent most of the time at partial throttle because it is much harder to get right......WOT took about 10 minutes........talk to Josh

 

My understanding of ECU flashes is that they only modify the stock programming for WOT conditions (open loop, I think), whereas a piggyback system (Like Spider's Unichip) can presumably be set up to alter conditions across the board. Spider, am I understanding this correctly?

Dominic, I think you're on to something here. Since the general rep of the MINI is to run rich under WOT conditions, I've wondered if the programming for closed loop conditions is also defaulted to run rich, and if it would be possible to improve the programming in that area. Sounds like you have the tool with your wideband to assess the program. I hope you find what you're looking for... this could be great for the MINI community.

 

Actually I don't have a tool to access the program.

I do have an APEXi II Select A/F controller which can fool the ECU to run leaner or richer at certain RPMs by intercepting and reprocessing ECU inputs forcing the ECU to run leaner or richer than it normally would for the same conditions it sees . As far as I have read, it has two A/F adjustment maps, one for WOT, and another for part throttle. I suspect that they have a setting for idle as well, but I haven't gotten that far into the instructions.

Before I make any changes I want to thuroughly understand what's going on. Hence this thread.