petrol guage/sender

[tourer-dan]

My car's fuel guage in't working properly.
When I fill it up to the brim, it only just registers past the 3/4's
Also, I refill it when it looks nearly empty, then only takes about 30 litres.
I've tried running it as low as I dare, then I managed to put in 50 litres (the fuel light has never been on since I owned the car, even though the guage needle has been resting on the stop)
So is my fuel light bulb blown or has the fuel never been low enough to switch it on?
I know the car has 2 sender units, does one work the guage and the other the light? or is it clever and works out an average from the 2 readings?

Any help much appreciated.
Also, what is the capacity of my tank? 325 touring.

[E30BeemerLad]

would be interested to see what replies are on this subject as mine starts to misbehave when i get down to below 1/4 tank, suddenly the gauge starts going up, usually showing a full tank. Is this just a case of replacing the sender unit?
1988 325.

Apologies for the hijack by the way

[Jos]

Yup, interested in this too, somedays it's ok, others the light comes on at 1/3 full, I have no trust in the thing...

Bet Brian comes back and says tighten the nuts on the SI board..

Also my batteries are flat on the SI board (can't reset the service lights) could this be a cause for the dodgy petrol gauge?

[tourer-dan]

HELLO!!
This is MY party.
[storms off]

[Jos]

lol, I did suggest that it might be the batteries:) Did that count as a non hijack?

[Gwynleym10]

Well the nut tightening theory does work.

I'm not sure if the petrol guague is affected by the SI bats, i thought it was just the rev counter and econ guage (as well as the service lights)

As far as the light, mine comes on when the needle has gone below red I can even have the needle going accross the orange light, so i can tell how much reserve petrol i have.

Only real way to test if it working is to buy a spare petrol container, and just run the car until you run out! you may well be surprissed.

You wont do any damaged (as long as you don't try and start it once its run out probably not even then.)..

Do it that once and if it works, you wont have to worry in the future about the guage.

[TouringMatt]

Just been through this myself

Temp gauge was becoming more iffy so stripped the cluster down and didn't realise id knocked the fuel need. Full tank read 3/4 and going off the OBC/mileometer, and what I ended up putting in at the pump, I was into the reserve - yet no light cam on

Changed the complete cluster ( cheers Taylor ) and sorted the temp problem, but found out fuel gauge read max all the time
Yet again going off what I knew took it into the reserve but no light came on, interestingly the OBC got stuck on 45 miles range!

Tightening the nut didnt work so finally reset my original fuel gauge, replaced it in the cluster and it all works!
Read full on full, reserve light comes on and the OBC starts displaying as it should.

Its like the needle position determines activation on the light and sends signal to the OBC

Matt

[TouringMatt]

Oh and my 89 325i Touring holds 50L + 10L reserve

Matt

[tourer-dan]

bump

[Brianmoooore]

Thought you'd all been sorted.
You've tightened the gauge nuts?
A faulty sender unit is possible, but unusual, unlike some later BMW models.
The two senders are series connected so it's impossible to sat which is faulty.
One of the senders and the low fuel switch are both contained in the aluminium can that fits into the fuel pump housing, but the two are seperate, although they use the same float.
Many people have posted on here claiming their low fuel lights don't work, but,as far as I can remember, they have all turned out to be fully working when their owners have been persuaded to push their luck a little further. The gauge is way down into the red before the light comes on.
There is no connection between the fuel gauge and the SI board and its batteries.

[E30BeemerLad]

so are these gauage nuts obvious? I presume they are on the rear of the cluster? I have never had fuel light on with needle on the bottom line past the red. mine just misbehaves and shows full when it gets low and just starting to go into the red.

[Brianmoooore]

Nuts are very obvious on the back of the cluster. Tighten the temp gauge ones as well while you are there.
Would expect a duff level sensor to act up at a certain level of petrol in the tank, rather than what yours is doing.

[tourer-dan]

Tightening the nut didnt work so finally reset my original fuel gauge, replaced it in the cluster and it all works!
Read full on full, reserve light comes on and the OBC starts displaying as it should.

Its like the needle position determines activation on the light and sends signal to the OBC

Matt

what do you mean by reset the fuel guage?
Mine seems like it reads about 1/4 tank too low, and as I said the light hasn't been on even with the guage resting on the empty stop. I wondered if the light had a separate activator from the fuel guage, and with the needle being inaccurate, the fuel has never in reality been low enough to put the light on. Otherwise if the light just comes on at a set point on the guage, then it is indeed, fucked.
Can I 'reset' what I have, or should I replace the guage or the senders? I have spares of them all.

God I've lost interest in all of this already and I haven't even lifted a screwdriver. Can someone just come round and fix it for me while I put me feet up?(for free)

[Brianmoooore]

By reset the gauge, he means bend the needle back where it should be, as he says he had damaged it.
Light is independant of the gauge. You should be able to tell if the light should have been on, by saving up your pennies, and filling your tank to the brim from as empty as you dare. If the amount you put in is less than 5 litres short of the total tank capacity, then the light shouldn't have been on.
If your problem is a constant undereading of the gauge, then your needle has probably been bent at some time.
If you have a spare, then stick it in.