Hi,

My fuel indicator is consistently off.

The average fuel required to fill the tank when the fuel indicator shows empty, (red light on and "0 Miles left in tank") is 12/13 Gallons. IF the tank holds 17 gallons, this seems way off even considering a conservative reserve level.

Is this an experience any else has?
Is there a way to calibrate the fuel level indicator to be more precise?

Any thoughts would be appreciated!

Thanks all!


FBS

 

mine is a bit different. fills fine but when full only reads 3/4 full

 

I think that's pretty normal. I've never filled much more than 13 gal. even after the light has been on and the miles remaining on the computer is pretty low. In fact, I think it's the norm on many other models of cars too. For example, in my Honda, it has a 20 gal. tank but I've never filled more than 16 gallons even after the light has been on and the needle has been pegged at the bottom for quite some time. The only accurate fuel level indicator I've seen is in our Volvo where you can really predict how many gallons it will fill by the number of notches above the needle on the gauge.

A more complicating factor for our 996TTs might be that the fuel level isn't really "measured" below a certain point in the tank. From what I understand, the fuel level is computed when you get below a certain level. That's why it won't even register if you just add a few gallons of gas when you're below a certain point (try it sometime -- the needle doesn't move and you'll think the gauge is broken).

At least the inaccuracy is on the conservative side. You should never run out of gas if you fill it up based on the gauge. Furthermore, it's probably not so great to be using up that last bit of fuel anyway, given the possibility of crud and sediment in your tank.

 

As mentioned above, the fuel tank has a hump in it and the sensor is in the upper hump thereby not actually recording the fuel level. Here are instructions for calibrating:

1. Disconnect the battery and cover terminal or battery.
2. Remove cap over the fuel level sensor system.
3. Remove fuel level sensor. ’ Rep. Gr. 20 66 19; Removing and installing fuel pump.
4. Using a fuel extractor, completely drain the fuel tank through the fuel level sensor opening. Fuel extractor:
Refer to the Workshop Equipment Manual, Chapter 3 "Workshop Equipment".
5. −Make sure that the two recesses on the left and right−hand sides of the tank are emptied
completely.−
6. Reinstall the fuel level sensor and, with "ignition off", fill the tank with −28 litres− of fuel.
7. Perform tank calibration with the Porsche System Tester 2:
· Select vehicle type (911 Carrera)
· Select control modules
· Select instrument cluster
· Select menu item "Tank calibration"
· Confirm calibration
8. The fuel level sensor system has now been calibrated.

 

yeah you have to put a lot fo fuel in it for the fuel level sensor to be triggered. After a certain point, fuel level is calculated, not measured.

 

can step 7 be done with the durametric?
would this solve the 3/4 full on the gauge when the tank is 4/4 full or does the fuel level need to be replaced?

 

Not sure on Durametric. I would call them. This procedure should be done whenever the sensor is replaced. No idea if this is your issue?

 

the miles to empty calculation is dead on. its the actual gauge on the dash that never reads above 3/4 full. since it was never a issue with running out of fuel i havent worried about it but its a little naggy thing i would like to correct

 

Are you sure it's full? Does it fill about 13 gal when the gauge is near empty? Does the 3/4 reading stay that way for a while when driving? Just double checking that you're filling it all the way due to that other problem of the pump shutting off early from the back pressure.

 

yes it is completely full. stays at 3/4 for a very long time then moves down

 

Durametric won't do the trick. I have read others have fixed the issue you speak of with the calibration procedure I posted.

 

^ guess i need to find the "porsche system testor tester 2" in my area.

 

Thank you ALL for the awesome information! I'm still not sure IF I should do anything about this annoyance, but do have a plan now IF I decide to try to make it more accurate.

Again, Thanks!


FBS

 

[QUOTE=Aerodude;3755783]A more complicating factor for our 996TTs might be that the fuel level isn't really "measured" below a certain point in the tank. From what I understand, the fuel level is computed when you get below a certain level. That's why it won't even register if you just add a few gallons of gas when you're below a certain point (try it sometime -- the needle doesn't move and you'll think the gauge is broken).[QUOTE]

Absolutely true and confirmed today! I put a few gallons of 100 octane to log some runs in a relatively empty gas tank and miles left ran down to zero and my gas light remained on! Guess I will have to do some calculations of my own to ensure I don't run out!