Ran out of petrol today with 15 litres left in tank!?

[OliHall]

Hi,

Today I ran my 07 v8v out of petrol.

The low fuel light had come on about one mile previous. I was about 1/2 a mile away from the petrol station when the car started to feel like it was running out of petrol. I was driving up a very slight hill, and after a few hundred meters, it stopped. The fuel gauge still had 1/8 of a tank left - the needle was on the first marker up on the gauge and the trip meter said I had 45 miles left.

Luckily I was only about a mile from work and someone was able to come and bring out a 5 litre can which once we put in, the car restarted. I assumed the obvious explanation of a faulty fuel gauge which was incorrectly reading high, and that I had run the tank dry. The car ran a little lumpy, but made it to the petrol station where I filled it up.

After putting 5 litres in the car from the can, I was expecting to be able to fit another 75 litres in the car's 80 litre tank and I was surprised when the pump clicked off at 60 litres. This meant that there was actually 15 litres left in the tank when it stopped and that the fuel gauge was actually reading correctly.

Now this is probably about the lowest that I have ever run the tank and I am interested to know if anyone else has had this problem with their car running out of petrol with still nearly 20% fuel in the tank?

Thanks,
Oli.

[Murph7355]

That seems very odd.

I am pretty certain I've had to put more than 70 litres in mine before (think 75 litres might be the most) - a number of times I've run it to the point where it stops estimating how miles the tank has left and just shows dashes (no room for "stop being an idiot and fill the tank up" on the display ).

How steep was the hill?

(It's generally not a great idea to run too low...though a bit hypocritical of me as I loathe filling up when there's a load of fuel left in it!)

[brianjone5]

Is that the first time you've had 'low fuel' light on?

It could be that the fuel indicator is correct, signaling 1/5th tank left and the gauge is correct, but the point where fuel is taken from the tank into the pump is misplaced and high.

I'd carry a can of petrol and see if the issue is repeatable. if so, then decide if you want to spend money fixing it.

[sadlerj]

I think they have a 77 litre tank, I have got 76 litres in mine before now with no worries about running out. I often have got more than 70 litres in, as I like playing those 'games'. I find the guage very accurate..

Edited by sadlerj on Tuesday 4th May 13:37

[Murph7355]

Just looked in the manual...fuel tank is 80 litres with approx 78 litres usable....not sure why you'd leave 2.5% of a tank unusable, but there you go.

[997GT3]

Does petrol not expand when hot - perhaps some of this 2.5% is for that?

[JohnG1]

Murph7355 said:

Just looked in the manual...fuel tank is 80 litres with approx 78 litres usable....not sure why you'd leave 2.5% of a tank unusable, but there you go.

Expansion room for hot weather to prevent emission of VOCs into the atmosphere?

Just an idea.

[GTDB7]

Does the fuels system not require that 2.5% to prime the system?

On mine a DB7 GT, it states in the manual that 7 litres is unusable as it is required to prime the system.

[rick-derby-]

unusual fault, would suspect fuel pumps sat incorrectly or the filter pickups not connected, as for leaving 2.5% in the tank, consideration has to taken for the pickup and the lower surface area, and also taking into account fuel movement between acceleration deceleration uphill downhill etc, a swirl pot helps minimise the effects of inertia but can't combat it completely,

[OliHall]

Grrrr. It's just conked out again. This time with 1/4 tank left.
Currently waiting for aston martin assistance at the side of the M1!
Going to get it recovered to newport pagnell.
Oh well, I hope this is covered under the newly purchased extended warranty!!

Oli.

[bacardii]

perhaps they leave some in the bottom so it does not suck debris through the system?

[Murph7355]

rick-derby- said:

...would suspect fuel pumps sat incorrectly or the filter pickups not connected, ...

Oli...sounding likely...??

[brianjone5]

Oli! you missed my 'carry a can of petrol and see if the issue is repeatable' post earlier.....

I hope you don't have too long a wait.

Brian

[OliHall]

Lol - Brian,

I was about to put your advice into action as my plan was to put a couple of cans in the boot when I got to work, but I was foiled when the car decided to stop this time with about twice the level of fuel it had when it ran out last time!

I am starting to suspect that it may not be fuel level related, and possibly an intermittent fault with something else in the fuel system. This is because after being sat by the road for 30min, it started up again and I was able to drive it on to the recovery truck. Also, when we unloaded it, it seemed to be running fine.

Oli.

[997GT3]

Faulty DME relay??

[OliHall]

What's the DME relay?

[997GT3]

OliHall said:

What's the DME relay?

"The Digital Motor Electronics (DME) relay unit is used on many Porsche and some BMW models. This is actually a double-relay-in-one component. The main relay is used to fire the DME control unit (computer), while the secondary relay gives power to the fuel pump and heater element inside the oxygen sensor. Failure in the injection system is usually related to the DME relay, but some technicians seem to have found a solution for it."

May or may not be relevant to AM's?

[spatz]

could be a problem with your tank integrated swirl pot, all tanks have it to allow consuming almost all of the tank without buidling a sump into the tank. The way it works is like the returned fuel is directed back in the swirl pot so the pick up line has always enough fuel (until even the swirl pot is empty)
if your return line is not feeding the swirl pot but the tank itslef it can happen that you can only use 75 or 70% of your tank.
most likely you cannot fix it but buying a new tank, so get used to the fact that 1/8 means empty

UWe