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    incorrect fuel gauge reading

    Hi all!

    Yesterday I had a breakdown with my 991 4S  Smiley

    I was on the way home .... but suddenly the motor stood still with "reduced engine output" sign ... the fuel gauge showed me remaining 57 km.

    Instead of calling porsche emergency number I decided to call my wife to bring some fuel.

    And what a wonder the car worked again .... I fueled about 8 liters and the fuel gauge climbed from 57 km up to 62 km only ... 

    I called Porsche this morning and they told me that Porsche knows about that problem but my vehicle identification number is not listed .... they asked me to bring the car for a recommended software update Smiley

     

    Anybody here with the same problem Smiley

     

    Best

    Gregor

     

     


    --

    -----------------------------------

    991 C4S * BMW X6 4.0d


    Re: incorrect fuel gauge reading

    Message: It's good to have a wife.....in emergencies angry

    This software update phenomenon is afflicting all cars of all makes. i wonder why these things are not shown and sorted during pre-production testing and they even appear after cars are in production for some length of time. 

    I remember, I was left stranded on a roundabout after my car lost drive, that was solved with a simple PDK update. That was a year after the system was introduced.

    Last month I bought a VW Polo which got me into emergency mode for no reason on my way to a weekend trip. Again it was  solved by a simple update, which shouldn't be required considering that the model was introduced in 2010.


    --

    "Form follows function"


    Re: incorrect fuel gauge reading

     I’m not happy with the fuel gauge reading, too.

    The PCM always shows a fuel usage about 10% too low. Every time I visit the fuel station I refill more fuel than I calculate by the shown fuel usage. So either the remaining kilometers are wrong (if the remaining kilometers are calculated by the fuel usage numbers) or the fuel usage number are intentional wrong.

    Both alternatives are not good.


    Re: incorrect fuel gauge reading

    Hi all!

     

    Yesterday I visited my Porsche dealer to get my software update concerning the fuel gauge reading.

     

    The congenial dealer told me that the bottom form of the tank on all four-wheel-models is a "W" ..... the gearbox divides the bottom of the tank in two troughs.

    The fuel signaler sits in one of them  ... and shows correctly the remaining distance .... but if the petrol sloshes completely to the opposite side where the petrol is leaving the tank to the motor .. the car stands stills suddenly.

    One can see this system while filling up a nearly empty tank ... if you only tank 10-15 litres the fuel gauge reading isn´t climbing because all the petrol first come to the side where the signaler ins´t placed. Starting with about 20 litres the petrol sloshes to the other side as well.

     

    Nice explanation ..... but it´s a construction fault ... isn´t it? mail

     

    The software update seems only manipulating the fuel gauge reading to show earlier a shortage of petrol.

     

    Best

    Gregor


    --

    -----------------------------------

    991 C4S * BMW X6 4.0d


    Re: incorrect fuel gauge reading

    Sidney:

    The congenial dealer told me that the bottom form of the tank on all four-wheel-models is a "W" ..... the gearbox divides the bottom of the tank in two troughs.

    The fuel signaler sits in one of them  ... and shows correctly the remaining distance .... but if the petrol sloshes completely to the opposite side where the petrol is leaving the tank to the motor .. the car stands stills suddenly.

    One can see this system while filling up a nearly empty tank ... if you only tank 10-15 litres the fuel gauge reading isn´t climbing because all the petrol first come to the side where the signaler ins´t placed. Starting with about 20 litres the petrol sloshes to the other side as well.

    Nice explanation ..... but it´s a construction fault ... isn´t it? mail

    The software update seems only manipulating the fuel gauge reading to show earlier a shortage of petrol. 

    The split tank design has been used on all 4WD 911s since the 996, including all Turbos, and is not generally a problem unless a driver puts less than 20 litres into an almost empty tank. Which is not something most drivers would usually do. 

    Not so much a construction fault as an engineering compromise to achieve the best possible result with the space available.


    --

    fritz


    Re: incorrect fuel gauge reading

    Hi Fritz!

    But if the car stands still suddenly even if the fuel gauge reading is displaying 57 km still to go ..... 

    .. is this also a compromise only?

     

    Best

    Gregor


    --

    -----------------------------------

    991 C4S * BMW X6 4.0d


    Re: incorrect fuel gauge reading

    And Sidney is not the only one with this little problem. The german forum has several 991 4s owners who are stopped by that.


    Re: incorrect fuel gauge reading

    Sidney:

    Hi Fritz!

    But if the car stands still suddenly even if the fuel gauge reading is displaying 57 km still to go ..... 

    .. is this also a compromise only?

    Best

    Gregor

    No, obviously not. Smiley   But your situation doesn't correspond to the problems experienced by 996/997 owners, who just discovered that if they only put a smaller amount of fuel into an empty tank, it would not show up on the gauge. Your dealer's explanation of the problem does not quite correspond to the nature of that experienced on earlier models. 

    Your problem would suggest that either the configuration of the tank or fuel level sensor system has been changed between the 997 and the 991 or the 991's fuel level sensor software needs to be improved. Let's hope that it is only the latter, as it would mean that it would just involve a software download.


    --

    fritz


    Re: incorrect fuel gauge reading

    So... is the fuel gauge signal in one half of the tank and the fuel outlet located in the other half? That would be the only logical explanation for that. 


    Re: incorrect fuel gauge reading

    Ferdie:

    So... is the fuel gauge signal in one half of the tank and the fuel outlet located in the other half? That would be the only logical explanation for that. 

    That would be the obvious explanation, but not the only logical one. Smiley

    Where the 996 and 997 were concerned, the gauge effectively worked down to the level where the tank divided into two "legs" which straddle the drive shaft. Below that level, the fuel level is "gauged" by extrapolating the previous fuel consumption rate based on the accumulated fuel injector opening times. Just educated guesswork, if you want to be cynical about it, but it works very well until someone partly refills the tank to a level which does not bring the fuel level back to a point which can be read again by the "real" level sensor. 

    Judging by Sidney's description of the problem he suffered from, the 991's fuel gauge may however have some different issues to those seen in the past on previous models.  Smiley


    --

    fritz


    Re: incorrect fuel gauge reading

    I have a really terrible habit of testing many vehicles fuel capacity limits!

    First was a 1978 Honda Civic 5 speed with about 36 city and 48 highway mpg! I ended up one day with my friend Dave and my little brother pushing my 1800lb car to the nearest gas station. It was only a block or two and reasonably level and they were young and quite able at that time!

    Over the years I owe thanks to Leawood911 and a few others for showing up on short notice with a gas can!!!

    My worst experience (logistically) was a Jeep rated at having a 20 gallon fuel tank. It actually turned out to be 18 gallon usable capacity and maybe 20 gallon actual capacity.  As a cop once told me while giving me a lift to a gas station, even if you have calculated remaining mileage once the low fuel level warning light comes on, why not fuel up when you reach the final quarter tank of remaining fuel?????

    Unless like back when I drove a pickup truck with a few extra gallons of fuel in the tool box (which helped more people than just myself) don't ever even get close to extremely low fuel level!!!!!!   


    Re: incorrect fuel gauge reading

    Hi!

     

    o.k. - I understand ... the last 15-20 liters is only guessing ... No senor available at the bottom of the tank ... the sensor ends a few centimeters above the bottom.

     

    That means if you had driven slowly to that 15-20 rest area .... and from that point you push the car very hard ... the fuel gauge reading is calculating wrong .... 

     

    Yesterday I received the software update ... it is available for 991 ... maybe this miscalculating is eliminated now.

     

    Cheers

    Gregor


    --

    -----------------------------------

    991 C4S * BMW X6 4.0d


     
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