V50 fuel calculator

I own a 2004 V50. The fuel computer must be inacurate. For example it will say 150 miles to run until empty tank when there is hardly any fuel left (low fuel light on) Even if i travelled at 20mph, I'm sure I wouldn't get 150 miles!
Is this a familiar story to anyone else?

[7050man]

Yes it is. You have to remember that the distance to empty figure will vary depending on how the car is being driven, so you may well get that kind of figure when the low fuel light is on.
One minute it may say 140 miles then if you get stuck in traffic or heavy with the right foot, figure may drop suddenly.
What engine have you got?

hi. it is the 2.0 litre diesel model

[7050man]

Me too. Got the E4 spec engine. It will go for miles with supposedly only a little amount of fuel in tank. What I have found is that even when guage is in red, you still cannot fill up the tank with as much fuel as you'd expect to get in.
This must mean that either the gauge reads on the low side (your not as empty as you think) or that there is some kind of air lock perhaps not allowing a full tank to be loaded loaded (unlikely).
My experience is that the guage reads on the low (very low) side as I regularly get between 450 and 500 miles out of a tank and still don't ever put more than about £43 in. Also I think that the fuel parameters in the computer err on the safety side.
Hope this helps.

[paul g]

Agreed,

At the moment I am showing 46.1 MPG with 90 miles left to go, but the needle is in the red. Quite often in my V40, if I drove steadily at say 60mph, the computer would start off saying I had 180 miles to go and then having completed a journey of 55 miles would then say I had 170 miles to go.

An old engineering friend said that owing to the fact that the car is not measuring 'linear' than it will not accurately reflect the 'real' amount of fuel. I suspect that whatever car you drive with or without consumption figs, one would never be able to put in the 'tank capacity' in terms of fuel

[4 forty]

http://forums.swedespeed.com/zerothread?id=34887

take a look at the above forum, which relates to the fuel gauge being out.

paul

[7050man]

Thanks for last post. A another piece in the puzzle perhaps.

Mention has been made of sensing system not being linear. What I suspect is not linear is the tank sender unit potentiometer(pot) as opposed to the gauge itself. Potentiometers are either linear or logarithmic (we've already established that from other posts).

What does this mean as far as we are concerned? Well, when the tank is full, a small movement of the float for a given amount of fuel used will not change the output voltage to the gauge by that much. However when the tank is almost empty, the same float travel will give a vastly different change in output voltage to the gauge because of the logarithmic rate of change of resistance of the potentiometer .

In real terms what we see when the tank is full, is full scale deflection of the gauge. The gauge does not appear to move that much in the first say 100 miles, but below half full reading, 100 miles may take it close on onto the red and move the needle by much more.

Most cars seem to have the pot wired this way round. An exception in my experience is the Renault Clio of a couple of years back. The rate of change of voltage output, seemed to be greater from full to half empty, than from half empty to empty.

Incidently, the temp and fuel gauges will not normally be set to work at full battery voltage due to fluctuations in charge. They normally run at a more stable 7 or 8 volts by use of a voltage regulator. I don't know specifically what voltage Volvos use.

What I don't know is how the driver info system dertermines distance to empty exactly. It must certainly receive instanteaneous data from the tank sender and also current load and fuel burn data from other engine sensors. Perhaps some one can shed a bit more light.

regards

[7050man]

Had a day in France today(booze cruise).
Owing to cheaper fuel, I didn't want to fill up here but I was showing only 50miles before empty, with the needle heading off the red on the wrong side.
I was sure I would be ok ( about 40 miles to Calais through tunnel from where I live), but I decided to put £5 in just to be sure.

First point. With guage reading this low and trip showing only a few miles before empty, £5 of diesel did not make the gauge or trip change. I've noticed this before at another time. Then I thought the pump had not dispensed any fuel.

Anyway due to slight tardiness and with train to catch, I had to blast down the M20, faster than I would normally have driven. At Ashford computer said I had 15 miles before empty and the needle was not even registering anything. At tunnel check in computer said I was emptywith _ _ _ in display. At this point I was abit nervous of stopping engine because I was not sure if engine management system woulld allow car to start if it thought that there was no fuel in it.
Second point: it did, several times with gauge not registering and trip saying I was empty.

Final point, when I did fill up, only managed to get in 43.47 ltrs.

No doubt that Volvo really don't want you to run out of fuel!