petrol gauge

[Alex]

Mine reads low all the time. When the light comes on I've still 4 gallon in the tank. One thing I've never solved on my car.

On a C4 it calculates the last amount of fuel due to the saddles , which is setup by doing a calibrate routine .. basically you tell the car how much fuel is in the tank when the gauge is at a set point.

Has to be done with a tester though.

Yes I'm fully aware how Porsche do the tank calibration routine, but I'm not convinced that's the problem. If I fill from empty, the gauge should ping into action when it has 19 litres in (on the C4). Mine doesn't come alive until I put about 28 litres in - which is the offset that my gauge is out (around 9 litres).

 

[deMort]

Mine reads low all the time. When the light comes on I've still 4 gallon in the tank. One thing I've never solved on my car.

On a C4 it calculates the last amount of fuel due to the saddles , which is setup by doing a calibrate routine .. basically you tell the car how much fuel is in the tank when the gauge is at a set point.

Has to be done with a tester though.

Yes I'm fully aware how Porsche do the tank calibration routine, but I'm not convinced that's the problem. If I fill from empty, the gauge should ping into action when it has 19 litres in (on the C4). Mine doesn't come alive until I put about 28 litres in - which is the offset that my gauge is out (around 9 litres).

Ive not had to do it for a long time but i think it was 25 litres you put in to calibrate it , it did change and Porsche modified it a while later so it could be 28 litres.

But i used to cheat , i prefered to set my own lvl as its not exactly an accurate system , there is a tolerance in the sender resistance that it will still calibrate , you can set it to the higher lvl or the lower lvl depending on just how close to 0 miles left and it will run out , i prefered over setting as many customers would run it very low.

I used to remove the sender and calibrate it by hand depending on the ohms reading on the tester.

Have you actually run the car past 0 miles and seen how far it goes before it runs out of fuel ?

Just an FYI , i rember a similar issue and i replaced the gauge .. the sender and the wireing and still had the same fault .. hence i came up with the above solution.

 

[Alex]

Yeah, i can get about 50 miles after it hits zero. When light comes on I have around 4 gallon in the tank.

 

[Alex]

Ps. Thanks for the info.

 

[deMort]

Yeah, i can get about 50 miles after it hits zero. When light comes on I have around 4 gallon in the tank.

Thats quite a big under read so definatly not correct but unless its really bothereing you .. and a fuel gauge is just an idicator of how far you have left then is it worth trying to fix .. I have tryed as i mentioned and all it did was end up costing the company a fair bit of money .. couldn,t charge for not fixing the fault .. and they are a dam pain of a system .. there must have been a better available system out there when they deisgned it.

Imagine putting in say 25 litres of fuel to calibrate when you have just drained it out and it says under filled .. so you add more .. under filled .. add more .. over filled and you have to drain it out and start again .. thats one of those jobs that i never forget doing .. hate them !

I was trying to fix a problem were the customer always put £20 of fuel in it , one day the gauge didnt register .. hence theres a fault .. turned out to be the cost of fuel had risen just enough that the car wasnt getting enough to register on the gauge .. had to tell them the the fault was to put £25 of fuel in it .. not change what i did to fix it .. opps.

Btw if you car ever had MUM on the reg then its one i set up to under read lol .. i doubt it but you never know.

 

[steve1]

Removed tank sender

 

[steve1]

Sorry for double post had trouble with pictures
Pictures are the old and new, the old has been bent double didn't know why until I tried to get the new one in.
The post is spring loaded and when it reaches the bottom of the tank it compresses. But the bottom of the tank is not flat and the post slides down one of the edges at the bottom of the tank which stops the sender going in square so will not fit properly. Who ever done this before has got pissed off and bend the post to get it to fit.
So question is how do you fit the sender without the post sliding down the uneven base of the tank, I'm not going to bend it lol

Hope this makes sense

Steve

 

[Alex]

was it in the right way round.....or 180 degrees out?

 

[steve1]

Right way round the point where it sits is quite narrow only about an inch across

 

[deMort]

It sounds like you have a collapsed petrol tank im afraid.

They fit fine with a small amount of compression normally but i have seen tanks collapse when theres a fault with the tank venting system .. it creates a vacum which collapses the tank.

Bottom of the tank should be flat and more than 1 inch.

 

[steve1]

Think you might be right then bottom of tank not flat
Have noticed that when I fill up there is a big inrush of air when I fill up looks like it will have to go to a garage lol *****
It must have been like it for some time last guy bodged it
Should the tank be perfectly flat

 

[deMort]

The last one i saw we couldn't even get the sender / pump out it was that bad

Base should be flat but to be honest i just fit pumps and senders without any problem so the shape of the tank is not something ive really noticed .. but lets face it , the tank has either been hit hard from underneath or has a venting problem for the sender to not fit .

My main concern is you get the venting side checked .. other wise you may end up fitting a tank only to have it happen again.

 

[steve1]

Problem solved collapsed petrol tank, when i removed the sender the post had been bent at 90deg, unable to fit new sender because the base of the tank had collapsed inwards.
So this was a problem that had been bodged in the past.
All fixed now but it took my new exhaust box money, will have to wait till christmas. (anybody want to invest in my christmas list)

 

[Junky]

When light comes on I have around 4 gallon in the tank.

I have the same,is this normal?
Ocassionaly when I fill up the gauge only reads 8/10 full until I switch off and turn the ignition on again.. Also the other day the red light came on,but when I filled up it only required 34 litres to top up which is just over 1/2 a tank? (The manual says I have a 65 litre tank..996 Turbo)
:?:

 

[steve1]

It sounds like the variable resistor on the sender is intermittent, or a poor conection at he top of the sender