Fuel gauge

I broke down yesterday on the M25, the fuel gauge said I had 5.5 gallons left and 112 miles before the next fuel stop. It lied massively! Does anyone know if this a common fault?

Yes it is. I think its a sticky sender. Mine only used to reset its self back to the correct value when i pulled up at a petrol station and added more fuel.

That sounds exactly what it could be, when I refuelled it gave the correct reading. Why couldn't Renault put a standard dial in instead?
I was returning from a day at the Goodwood festival of Speed and had several supercars behind me, a rather envious Esprit driver kept undertaking me giving the thumbs up at my car before I pulled into the hard shoulder (maybe it should have been thumbs down?!)

Strangely enough, I have been suspicious of my fuel gauge since the last fill up. I only noticed the day after that it was showing 8.5G. I had let it run below the 1.5G indication and then put £20 of fuel in so it couldn't possibly have had 8.5G. I'll try and fill it up again and see if the reading drops relative to how much I put in.

Is there any way that you can tell exactly how much petrol is in the tank, other than draining it all out?

Also, I presume that the fuel consumption figure will be correct as is derived from fuel flow rather than the drop in the tank so perhaps I could reset the computer and check if the fuel consumed (i.e mile travelled/average consumption) matches the drop in the gauge reading.

After your A3 story, I'm now hoping that I can get to the garage before I run out!

As far as I can deduce after 10 years of observation, the fuel gauge on the trip computer normally (?) works as follows:

1. The tank fuel level sender is only read when the ignition is turned on, or the battery disconnected etc.
2. While the car is in use, the fuel gauge reading only reduces by the amount of fuel going through the fuel flow sensor - i.e. the tank sender appears not to be consulted at all during normal running.

Now the killer - if the fuel flow sensor is dicky (e.g. drying joint on speedo etc circuit board) - the true fuel flow will not be recorded, and the fuel gauge will read high.

3. If you add fuel, >taking the tank level above the current fuel gauge reading<, the trip computer will be register the increase when you next turn the ignition on.

(now another killer).

4. If on starting the fuel level in the tank is lower then the trip expects, it >doesn't< appear to register the drop in level - it assumes it must be an error and ignores it - after all, if the fuel hasn't gone to the engine via the flow sensor, where has it gone?

The system has a sort of logic (fuel can only go in to the tank, and out to the engine!) - but it doesn't fail safe if any of the senders are faulty.

Putting the trip computer into diagnostic mode (disconnect battery, wait 30 secs or so, reconnect, press computer mode/function key and hold 10 secs - do not press trip computer reset) gives direct tank sensor readings all the time - though this will fluctuate if you are on a slope or there is heavy eletrcial load (e.g. lights) - used like this the tank sensor has no averaging capability and the reading depends on battery voltage, as this wasn't how it was intended to work.

Mark.

I am finding that my trip computer is using much more fuel than it really is.

I though I was suffering a mega rich running problem, getting 20 instead of 30 mpg, but yesterday, sudddenly I had 6.1 gallons in place of the 2.9 I had the previous weekend when last used.

I tried putting it into diagnostic mode, the reading seems to be cycling around, up and down by a gallon. I have yet to drive it in this diagnostic mode, but will it stay in diagnostic mode after the ingnition has been off and on again?

Hi Simon,

Firstly thanks for the radio tip disconnecting for a while then reconnecting did the trick.

Now the fuel, when I bought my car a year ago it came with Marks letter above printed out and has been set in the emergency setting ever since. This actually works very well if you can live without all the trip information, (I can knowing the mpg could be depressing) but it does meam having to press the reset button on the left side of the dash at every start up.
I believe in this setting just the the sender information is used for the gauge and the flow meter is redundent.
The only oddity I have noted is that when the lights are on the gauge shows exactly one gallon less than when off Otherwise it works very acurately, so far

Steve.

If it helps, I will have a new gauge in stock soon which is a digital type in either blue or red with silver or black bezel..

Now the fuel gauge one is £49.99, can work and calibrate with any type of sender, and reads simply from 0% to 100% fuel level, so you simply fill the tank, press calibrate, and then empty the tank (or as low as you want to let it go) and calibrate that as 0%

The unusal thing about the fuel level sender is that when the tank is full, the resistance is at its greatest, unlike any other fuel guage that I have played with.

In most cars the fuel guage is basically a volt meter that reads full scale when the tank is full because there is no resistance in the circuit, and so reads lower when more resistance is introduced as the fuel level drops.

Of course the Alpine had to be different.

So full = max resistance, and empty = min resistance.....

Are you sure its just not because your upside down over there?

I think GTAs have all the same problems in Aus as in GB. Like your cars, most of the problems are electrical, but I have had prior experience with a Renault 25 that broke me in.

I admit though that if a GTA was sold here new, it would never see the rust or the corrosion of bolts and fittings that you do though.