jhalliman

Hey all,

I'm running the Fabspeed GT420 kit on my 981 GT4. I had a few codes throw which they fixed for me quickly and I appreciate that support. I'm getting a persistent P0660 code, so I figured I'd datalog the car. I'm finding that the AFR is running fine during pulls themselves, but I'm getting some crazy values when I left off throttle. I don't know if these are actual concerns in the way that the data is being logged or whatnot, but they seem nuts to me in that I'm getting AFR readings as low as 10.88 but supposedly as high as 44.54. Feel free to see the datalog here: https://docs.google.com/spreadsheets...it?usp=sharing

You'll notice that the AFR goes wacky only on gear changes, and only if you're in gear and coasting off throttle, not under load. I am not a tuner nor do I profess to know the first thing about tuning, so I'm just curious what everyone's opinion is on this.

jhalliman

Reading now that the ECU may just shut injectors off to fuel conserve, which would make a ton of sense why there is no fuel in the ratio, but I figure I'll leave this here in case I'm wrong.

user1029

Don’t trust AFR readings with throttle body closed on decel/braking

while idling in neutral the AFR should not be wacky

jhalliman

That’s good. Car appears to be fine in neutral idling. Just reads what is probably max AFR with the throttle body closed due to the computer trying to calculate infinity haha. Appreciate the info. If nothing else, this tune runs a bit on the rich side under load and safe on idle, so the rest of the data says it’s very safe.

A432

Yup the SDI DME shuts fuel off on coasting in gear, that's what you're seeing.....if you barely tip in to the throttle downhill next to the divider/wall you can hear the exhaust "pop" as fuel comes back in

AO

Agree that this is a result of fuel being cut off on lift. What I don't agree with is the values. Atmosphere O2 levels are ~20%, so on lift you should see something in the lowish 20's not 30's and 40's. But under acceleration the values look to be spot on. On my supoercharged 928 I shoot for 12.5 under WOT at 5k+ RPM.

A432

Lambda is air/fuel ratio not oxygen percentage of air ie. 14.7 parts of air to 1 part fuel which is stoichiometric as an example. The computer stops measuring at the 44.54 point as the ratio being infinity ie. all air

DR.S

Why are Lambda AFR values not "high" all the time in deceleration phase?
Due to fuel cut off they should??

A432

I believe it's due to the program to make the burbles sound.

DR.S

I wonder if the low lambdas are due to running into engine protection because the tune is not "100% right"...