paradocs98

A heads-up for those of you who track your 991s--be mindful of the fuel level. I normally don't stay on the track when the fuel level drops below 1/4 of a tank, but on occasion I'll run a couple of more laps before coming in. Running a bit below 1/4 of a tank was never an issue with my 2011 M3. But today with the 911 at NJMP Lightning I pushed it a bit, and got down to about 1/8 of a tank. The response was not good--in the Lightbulb, a big, sweeping bowl-shaped turn, the ECU must have detected the onset of fuel starvation and decided to cut power, putting the car in "limp" mode. So, imagine being in a large, sweeping turn, balancing the car on the edge of traction between understeer and oversteer at about 80mph, and suddenly having the ECU effectively hit the brakes by cutting power. Not fun. Luckily I sensed it and caught it before the back end could come around.

Lesson learned--when the tank gets to 1/4 full, come back in.

(Note: this was a new, different scenario compared to my previously- experienced PDCC faults on track. The PDCC faults occurred in constant, hi-G loading corners that seemed to overwhelm the PDCC sensors, regardless of fuel level. "PDCC fault--possible to drive on carefully" came on the display with those instances, and the ECU booted the car out of Sport Plus into Normal/"Comfort" mode, reducing throttle and suspension responsiveness, but NOT cutting power. This situation with low fuel today was distinct. Power was definitely cut, and something like "Engine fault--possible to drive on at reduced speed" was displayed.)

StudGarden

Nice. When in doubt, shut the engine off an unload the suspension. For safety, of course. What's next, when it detects too much braking just disables the brakes? Why not go all the way and put ejection seats that automatically launch at any and every potential issue.

chuck911

Cars have always gotten fuel starvation in situations like this.

fbroen

"Luckily I sensed it and caught it before the back end could come around."

Did you catch the car or did the car catch you?

Hammer911

hey Chuck - how do the "real" race car handle this issue?

chuck911

You're confusing me with the scare quotes. Not quite sure if by "real" you mean really real as in really racing, or if the scare quotes are ironic as in LeMans, where they pretend to be racing when really its more like one of those college teams trying to see which car can go the furthest on a drop of gas.

That at least would be a discussion worth having. This one, I just don't get at all. I mean, for like about a decade I was doing autocross, which if you're serious you just don't ever show up with more than about half a pint more gas than you need to do your runs. So of course every once in a while you get fuel starvation. And by starvation I mean no gas at all. Not some soft easing off, just no gas, none, nada.

Now that I think about it, autocross is real racing. Really real, no scare quotes. We handle it by driving.

John's 991

Thanks for the heads up I guess I have been lucky, as I have frequently run the tank down to an indicated 1/4 tank when on the track. The early fuel warning is a bit annoying but can be lived with. Perhaps I have not been in a long enough sweeper....

Larry Cable

Yup, its called 'ice mode' ... seriously.

paradocs98

Exactly.
Absolutely--but instead of the expected sputtering from the engine, the 991's ECU gives you sudden donkey-digging-in-its-heels mode, which is unwelcome mid-corner at high speed.
Since I had disabled stability control, luckily I was the one doing the catching.
Glad to be of service.