As I mentioned on another thread, I had to get my brand new C4S towed because the fuel gauge indicated 1/4 tank full with 66 mi range when it was actually completely empty. I took it in to a dealer initially who felt it was a faulty fuel sending unit, and suggested replacing it which was back ordered to Germany. I then took it to my local dealer today (this happened while I was traveling), and they "calibrated" my car's fuel sending unit, and told me everything is functioning properly now. They asked me to monitor the fuel gauge & miles range estimate closely to see if there is any issue. They did tell me that the C4S and turbo fuel tanks are unique in design & makes it difficult to measure fuel amount accurately when it runs low. However, to me it seems unacceptable if it gives a quarter tank remaining with 66 mi range remaining when there is actually no gas left. I'm alo confused whether "calibration" can actually fix this problem, or was just a diagnostic test.

I plan on letting the gas run low below 1/4 tank and see how the gauge & range correlate. Would be nice to get input from other C4S owners. Thanks!

 

Yup, I just joined your club
same issue here on '13 c4s, got towed back to dealer only to diagnose the car was out of gas...
They are now doing the 'recalibration' thing, although a quick google will reveal this being a well known issue for many many years now mainly due to the saddle-shape of the 4S tank architecture...

 

Sorry to hear your baby had to get towed! I know how that feels!

Calibration seemed to have helped with my car. I ran it as low as 30 mi range remaining, and was fairly accurate. I think the estimate range @ the level becomes "calculated estimate" rather than actual measurement when about 1/4 tank is remaining. This means as long as your driving condition is fairly constant, this estimate will also be fairly accurate. But when the driving condition changes significantly such as long highway driving, this estimate can get way off. At least for me that seems to be what happened. I drove down to LA from SF and the fuel gauge basically got stuck at 1/4 tank with 66 mi range. I'm wondering if the estimate was based on 25 mpg of highway driving when I was actually back doing city driving. That's my theory, but the bottomline is I now fill up that tank when the light comes on!

 

Schunmd: I haven't gotten into this problem yet and hope that I won't. I took it to Monterey /Carmel the 2nd day I got it and then drive over 200 miles last weekend as well. I have to say that I continue to fill up the tank when it's 1/4th or more left due to the issue you reported. Thanks for that.

I have my 60 day wellness checkup on 3/26...I will ask them to check it out and "calibrate" mine too. Lets see...seems to be very odd issue! Don't like it

 

I'm going to pick up my C4S in about 1 month and this problem is worrying me! It would annoy me a lot if I have to keep filling up when there's still 1/4 left. It's like the fuel tank suddenly became 1/4 smaller in terms of worry-free driving.

 

Wow -- those of us with earlier models (at least 996s if not earlier) have had this issue. Fuel is only measured from full down to a certain point, then it's calculated. I don't know if the 991 does the same thing, but if I add a few gallons into the tank when the fuel is low, the gauge won't even register anything unless you fill it up to a certain point.

You would think that the technology Porsche uses to determine fuel level would have advanced enough in the last 14+ years that they would have figured a better way by now. Oh well -- that's one of the reasons I try not to run my tank so low.

 

You would also think with the many thousands of testing Porsche does in these cars that this issue would have surfaced somewhere along the way.

 

Sorry for your issue. Hope it's reliably correctable. Aren't you glad it was your new car instead of your new airplane.

ChuckJ

 

I was told turbo fuel tank design also has this issue?

 

Hehe. This is why we poke measuring sticks into our wing tanks during preflight. The airplane only needs to be certified to have them read correctly when completely empty.

 

Yup -- this issue has been around for at least a decade.

 

This is not good news. Need to take this into consideration at the track.

 

Good point! You don't want extra weight in your tank, but don't want to run out either!

 

Always want to keep the fuel pump under fluid to keep it cool. With all the movement during tracking Im sure the computer is going to have a hard time giving you a accurate fuel measurement out on track if its getting under 1/4 tank. Worries me a bit, but I guess we will just have to deal with it.

 

Ironically, I haven't had much of an issue at the track. I usually try to have a full tank when I start out in the morning. In some ways, driving on the track is pretty consistent in terms of mpg (<10 ), so the calculation for the computer is straight forward. I think the gauge is pretty accurate throughout and I add fuel at around 1/4 tank. Also, although there might be some unhappy fellow drivers, it's actually less hassle for you to run out of fuel at the track than on the highway -- not that I'd ever recommend it.