Details:
2009 Mini Cooper S
Second owner
14k miles(bought at 6k miles)

Mods:
Defenders of speed CAI
Custom stock sized straight pipe from before the second cat back.

Basically a local shop was having a dyno day today so I decided to take the car down to see what it was making before I bought a acessport. Car made 179/205 but with AFRs of 14.3 until 5k rpm then they go down to about 12.5.
Obviously this is extremely lean for the car being under load and is not safe. I have a Scan Gauge II and it is saying the car is staying in closed loop till about 5k rpm and then switches over to open loop. Anyone happen to have a idea as to what is going on? Will buying a accessport alleviate the issue?

Graphs:

 

They hooked it up wrong. Happened the first time I dyno'd mine too.

 

hooked it up wrong how? The only thing they attached to the car is a wire to get a tach signal and the sniffer out back by the exhaust.

 

AP will alleviate it but, so will a tune.

 

12.5 is going rich, not lean

wipipedia:
A stoichiometric mixture is the working point that modern engine management systems employing fuel injection attempt to achieve in light load cruise situations. For gasoline fuel, the stoichiometric air–fuel mixture is approximately 14.7; i.e. for every one gram of fuel, 14.7 grams of air are required (the fuel oxydation reaction is: 25/2 O2 + C8H18 -> 8 CO2 + 9 H2O). Any mixture less than 14.7 to 1 is considered to be a rich mixture; any more than 14.7 to 1 is a lean mixture

scott

 

im talking about 14.3 afr being lean but yes 12.5 would be infact richer.

Maybe its just me but 14.x air fuels should be way too lean even for a direct injected motor but 12.xs should be fine.

 

the afr needs to be near stoich most of the time or the cat will die

modern engines are designed to run leaner, mostly due to the precise monitoring and fuel delivery systems

older designs, ie carbs had to run rich due to variations in mixture delivered to different cylinders due to many factors

i would not be worried at all by the observed afrs in your engine

when i managed a land-speed record team in the 90's, running turbos at 70+ pounds of boost, we looked for 14.1 afr

btw we set 2 world records

scott

 

alright thanks for the help

 

14.7 is a target AFR for when the car is at idle, or when at light throttle or cruising, but for sure not what you want when at full throttle. Running 14.7 at full throttle will cause a lot of knock, and really high EGTs.

When at full throttle, a safe AFR is 11.5. Jeff made a blog post helping to explain this a little while back.