Hi All,
Have recently noticed that my fuel warning light activates earlier than it used to,
does anyone have any experience with this problem and if so what do I do to rectify it.
Light comes on midway between 1/4 and 1/2 way point.
Realize this is not of earth shattering consequence but it still annoys the crap out of me.
Model is a 1985 911 3.2
R. Dave

 

Your car's fuel gauge sending unit in the tank is probably failing. Always trust the light, never trust the needle! If you drive/consume using your trip meter you'll know "how much" gas you have left, but if you disregard the mileage driven then you have to trust the gauge. Remove the trunk carpet at the brake booster corner, pull it down until you can see the top of the gas tank. In the upper corner you will see a round metal part held on with 5 small nuts. It will have a wire connector in its middle, pull straight up on the black connector and move the harness to the side. Remove the 5 nuts/washers and pull the disc straight up - slowly! It will have a tube connected to it, and the wires are inside the tube. As you remove the sender gas will drain out of the tube into the tank. When you have the sender out check its bottom. Nut missing? If not, turn the sender upside down and then upright again. Float inside the tube slide smoothly?

Based on experience you should probably just order a new sender, but that might not be the issue. Chance of a bad sender is about 95%.

 

Hi Peter,
Thanks for the advice.
Have pulled the sender and it appears to be working OK by the multimeter.
Will probably just have to wait and see if it gets worse and requires replacement.
I will work to the advice of the warning light and not the gauge, don't want to be stranded. I'm notorios enough when it comes to filling up, it drives my wife insane.
R. Dave

 

Nice points, Pete.

Watch that trip odo per usage to differentiate the 2 separate things Pete points out. Haven't checked the Bentley nor worked in this area but will review any resistance readings that the float should provide.....definately want to know about the "5%" category, as to insrumentation functionality.

I'm usually of the school to get old sheeit OUT of there.

Best,

Doyle

 

Ok, thought some may be interested in the rig I set up for getting a real time look at what the fuel gauge was doing out of the vehicle.
I first checked the parameters as per the the manual [see chart attached] and that appeared to be fairly close to spec, a little short on ohms at both ends but near enough. I still wanted to see what was happening though so I decided to set up a test rig and observe first hand what was going on.
The first thing to do was replicate a fuel tank and it occurred to me that the simplest way of doing so was a length of 50mm PVC pipe cut to a slightly longer length than that of the sender and fit an end cap to it. Voila. A petrol tank. I then tapped in a barb at the bottom and fitted a length of fuel line so I could control the amount of fuel in the chamber and watch, when wired up, how the gauge responded to flow. It would also show when the low fuel light would activate and at what level on the meter.
Turned out to be a worthwhile exercise as it did demostrate that the components are working correctly. If it still reads wrong in the vehicle I can only assume that there is something else going on. It did conclusively prove to me that the light is the main thing that is to be believed as it cannot be wrong.] Having pulled the sender apart and checked out the way it activates it can never be wrong.
I realize that some might figure this may be a bit **** but those sort problems are always in front of you when you drive the car and to me at least, are a constant source of annoyance. Can never rest until I get get to bottom of the problem. It may never marry up properly whilst in position but doesn't really matter the main thing is that I now fully understand how it works and what is going on with it.
Dave

 

Well the results are in.
All is working spot on.
Checked the continuity at the sender 67.2ohms and 67.3 ohms at the dash terminals, so no resistance errors there.
The next thing thing to do was put the gauge back in the dash and see what it reads.
The meter indicated exactly as it should. The only thing that I can assume is that there was a build up on either the the resistance wires in the sender or the terminals. They were all cleaned so that could have been the answer to the faulty readings.
What ever the reason all is well with the world again.
Hope it was all of some interest and help.
Dave