Strange Petrol Gauge issue

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Neilsouth
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Strange Petrol Gauge issue

Post by Neilsouth »

I have a Citroen Xsara 1.4 , bought it few days ago..

I drove the car back from its place of purchase and when i got back it had half a tank of petrol. I live on a slight slope so i expected the gauge read out to be slightly different. The next morning the car showed under half before i started the car. I drove the car round and it was still just under half a tank when i got back home.

I didn't start the car right away the day after and my petrol gauge showed just over quarter , i thought maybe i had a fuel leak but nothing seen. I drove the car about and the fuel gauge still showed just over quarter when i got home.

Here's the strange thing today , i parked near the sea front went for a walk came back started the car up and it showed Half a tank and even on the slight slope at home Half a Tank...

Is the petrol float in the tank giving slightly inaccurate read outs?
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Post by wheeler »

Im afraid that it seems to be a quirk of the xsara, they are famous for erratic fuel gauges, changing the sender wont make a bit of difference.
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Post by Paul-R »

I'd much, much rather have the fuel gauge in the Xsara than the computer controlled abortion that's fitted to the C5.

I just SO don't trust the C5 gauge. I keep a note of the mileage so that I can be reasonably sure of what is really in the tank. If there was a way to take the ECU out of the chain I'd do it. At least then the gauge would show what the sender unit is reading rather than what the ECU "thinks" I should know about what, just possibly, might be nearly approximately in the tank.

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Post by Neilsouth »

:lol: Well i'm glad its normal then , what car to this day doesn't have the odd quirk/problem even when new :lol:
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Post by myglaren »

Paul-R wrote:I'd much, much rather have the fuel gauge in the Xsara than the computer controlled abortion that's fitted to the C5.

I just SO don't trust the C5 gauge. I keep a note of the mileage so that I can be reasonably sure of what is really in the tank. If there was a way to take the ECU out of the chain I'd do it. At least then the gauge would show what the sender unit is reading rather than what the ECU "thinks" I should know about what, just possibly, might be nearly approximately in the tank.

Rant over!

I have been impressed with how linear it is.

I always fill to the brim then run it until the red light comes on, then refill.

At first it was taking up to 72L but now seems to take 62-65L.
Always reset the trip and depending on type of motoring it gives the same distance between each segment.
Trip computer doesn't work though.
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Post by Paul-R »

myglaren wrote:I always fill to the brim then run it until the red light comes on, then refill.
If you fill it to the brim (as I do), then the computer doesn't actually know how much fuel is in the car because TSU (tank sender unit) reads maximum when it is pushed to the roof of the tank and can't read any more as the fuel level rises up into the neck.

So. the computer thinks that the fuel level is tank maximum. The computer then ignores the minor variations from the TSU which will start lowering when the fuel level gets down to tanlklevel. The computer only takes note of the TSU when more than a certain quantity of fuel is put in, somewhere around 10 litres but certainly not as little as 5 litres. This means that if you put 5 litres from a spare fuel can it's totally ignored. Similarly if you fill the car up with fuel from 25 litre containers (ahem!) and then top-up the last 5 or so litres at a fuel station to get a brim reading, this is also ignored. You drive out with the gauge reading just under full.

Like I say, I prefer the Xsara. If I can get 50 miles before the gauge starts reading less than full after a brimful, then I know I'm doing OK for fuel consumption. If I get nearer to 70 miles then I'm doing very well. Similarly if the trip reads 300 miles when the gauge reads 1/2 then I'm doing OK. 320 miles is good - and you get the picture.

Just try that in the C5 - it's all over the place.
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Post by _kid_ »

Totally normal behavior for a Xsara petrol tank gauge :D I have same model and find if i park the drivers side on the kerb it reads lower. If i park passenger side on kerb it reads higher- i don’t need to tell you how i park my car :D

but parking on level ground for around 10mins or more and i get a reasonably accurate reading.

plenty more ino on this on the forums at www.cxoc.net/
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Post by myglaren »

Not sure I follow what you are saying there Paul-R.

I filled mine last week and it took 62.81 Litres, which has been the norm for the past year.

I usually just use the car for work and shopping and clock up 100 miles a week. Each 1/4 tank is indicated after each 100 miles travelled.

However, I did a 200 mile journey a couple of weekends ago that skewed the readings as I managed an additional 105 miles from the tankfull*.

The readings are always consistent though, as long as journey types are the same.

Since the last fillup, I did 38 miles before the needle moved.

It seems to me that it is now registering empty while there is still ±9 Litres remaining, while previously it registered empty when there were just fumes in there.

One day I'm going to pull that sender unit/filter and see what sort of a mess it is in.

Not today though :)

*-which may be partly attributable to using Total Excellium Diesel, or not.
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Post by Paul-R »

The long and the short of it is that the gauge does not reflect the position of the TSU.

If the warning light comes on in the Xsara I can put 5 litres in and the light goes out and the gauge moves slightly. Ican then safely drive a further xx miles until the light comes on again. Not the case with the C5 which knows better than to believe that I would dare to put such a small amount in. I have to add a further 40 odd miles to the however many miles it tells me are left.

In fact the more I think about it the more I can feel my rightous indignation welling up. I can't believe that I'm the only one who gets exercised by this!
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

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Post by Neilsouth »

Well i just checked it now , the car is on a slope leaning on its left(?). I didn't turn the car on only to check the fuel gauge.

It's now only just showing over red , which concerns me! and it will probably stay like this while im driving. But if i find a straight bit of road , reset the car it will probably read under half a tank.

This car is getting more and more fustrating and i got it in the hope it save my issues after my mr2 turbo.

:x
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Post by addo »

You can do some reasonable calcs over a few weeks to work out "safe" mileages per tank under varying conditions.

At the risk of sounding a little harsh, you could have a far worse state of existence than erratic gauges create.
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Post by Paul-R »

@Neilsouth

Sorry for banging on about my problem but could I suggest that you do as I do and carry a 5 litre spare fuel can in the car?
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Post by RichardW »

It's to do with the gauge not actually repeating what is in the tank, but what the ECU thinks is in the tank after doing some 'calculations' based on what was on the tank the last time it thought to look at the sender (which might only be at start up), how far it's been driven, and what the consumption has been / is forecast to be. I don't know why the gauge couldn't simply give a reading of the contents by being 'pinged' by the mutliplex every minute or so - obviously the Citroen software guys thought they could do better!

There must be some element of this in the Xantia MK2 fuel gauge too - as once the light has come on, it stays on till refuel - no flickering round corners / up hills like they used to. The Visa one in the PRN cars was woefully underdamped, and would ready anywhere between 1/4 and 3/4 depending on the corner - even in the mighty 35 BHP twin cylinder 'Special' :lol:
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Post by Sid_the_Squid »

I agree with addo, forget the fuel gauge, its a guide, not a technical manual. After 2~3 tanks you should have a fairly good idea how many miles the car will do before your out. Try driving an LPG car, the gauge on those is even worse, as reacts to the expansion and contraction of the gas based on atmospheric pressure.
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Post by Paul-R »

RichardW wrote:It's to do with the gauge not actually repeating what is in the tank, but what the ECU thinks is in the tank after doing some 'calculations' based on what was on the tank the last time it thought to look at the sender (which might only be at start up), how far it's been driven, and what the consumption has been / is forecast to be. I don't know why the gauge couldn't simply give a reading of the contents by being 'pinged' by the mutliplex every minute or so - obviously the Citroen software guys thought they could do better!
Exactly my point!

And they can't!
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

"Trying is the first step towards failure" ~ Homer J Simpson​
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