good christmas eve afternoon to you all!

drove up to mackay from the gold cost, and used / put in TWO full tanks to get here.
so thats 71L x 2 tanks = 142L right?

trip computer was showing thismorning that we have used 116L of fuel - so in theory i had around about 25L to bone dry correct?

filled the car up - and it took just under 68L to fill.

do you see my problem?

if i had approx 20L (for ease of adding) left, and i added another 65L (ease of adding again) i would have then had 85L in my 71L capacity tank!

BUT

if the pump at the servo was correct, and it did take the 68ish L, then i would have had around 3L left in the tank - and the trip computer was wrong and told me i haddnt used enough fuel!

before filling the car the very first time to come to Mackay, we reset all meters (avg speed, fuel, L used, odo etc) so that ini theory we would know how much we had to use to get here - so it wasnt reset after say 15L had allready been burnt, we did the reset before we left to avoid that problem.

i checked that the computer has been told its correct parameters (by holding SET and turning to ignition) and its told me 4D (awd) and 3.5L - so thats all correct, which is good.

for the record - the car is using extra fuel than it needs - on the way up we got a best of 9.8L per 100km avg - which is around 2L / 100km too heavy, so we think the O2 sensor is starting to die.

this is a worry for me in that i tend to drive around by L Used instead of DTE because my fuel system (guage) is still in the process of getting fixed - for the THIRD time (well when i get back to the coast)
and i only start to get worried when i have used more than 60L (11L remaining) and put more juice in, as DTE had allready started flashing at me 20L used ago!
im not a leadfoot - but i do occasionally enjoy giving it a boot off the line to be first to merge etc..

so - is the pump more accurate, or is the trip computer more accurate.

oh - when we did the fill on the way up/ on the road, the L put back IN matched very closely to the L USED.

cheers
Hope everyone has a FANTASTIC christmas tomorrow - and when on the roads are safe

Hmm we did a trip to Qld from Tas and my calculations compared with the cars was only out by .5l or so, bascly SFA pretty oddd....

someone with a bigger brain come on soon and help ya out hahahah

Cheers mate a have a great Xmas :)

Heath

i'd say the pump is more accurate. all it takes is 1 dodgy sensor in the car and your computer is out of whack.

9.8L/100kms isn't that bad. you have to take into account average speed as the main factor into your average fuel economy, plus terrain, tyre pressure, air temp and amount of stuff you have in the car before you say it is bad. it seems fine when i compare it to what i have gotten out of my 2 manual TH's on the highway (usually low 9's, depending on how many people in the car).

when you filled up the first time during the trip (not the time before you left) how much had it used? you said it matched pretty closely to what you had used, but how much was it. then add 68 onto that and it should tell you exactly how much out the computer is. and it obviously only happened on the second tank. that is where your maths could be way out. unless you put in 71L the first time then there is no point in using it in the equation. just use the 68 that you put in plus, the amount that you put at the first stop during your trip. then compare that to 116L. (116-68= 48), so if you put in more than 48L at your first stop then the difference between 48 and the amount you put in is how much your computer was out on the second leg of the trip.

Nevermind, somehow breezed over that you'd checked the trip computer setting ;)

Is a gimmick.:bowrofl:

Very likely what you pump at the station reads exactly what you used.
The computer is only doing some maths and like ppl said it depends on its sensors. On a hill slope may read less or more.

i'd say the pump is more accurate. all it takes is 1 dodgy sensor in the car and your computer is out of whack.

9.8L/100kms isn't that bad. you have to take into account average speed as the main factor into your average fuel economy, plus terrain, tyre pressure, air temp and amount of stuff you have in the car before you say it is bad. it seems fine when i compare it to what i have gotten out of my 2 manual TH's on the highway (usually low 9's, depending on how many people in the car).

when you filled up the first time during the trip (not the time before you left) how much had it used? you said it matched pretty closely to what you had used, but how much was it. then add 68 onto that and it should tell you exactly how much out the computer is. and it obviously only happened on the second tank. that is where your maths could be way out. unless you put in 71L the first time then there is no point in using it in the equation. just use the 68 that you put in plus, the amount that you put at the first stop during your trip. then compare that to 116L. (116-68= 48), so if you put in more than 48L at your first stop then the difference between 48 and the amount you put in is how much your computer was out on the second leg of the trip.

average speed from the trip computer was about 85km/hr - if not more, i cant remember the exact number now, as i have been doing a bit of town driving which drops the avg speed TC a lot.

just gone through my motorcharge vouchers (company fuel cards rock - esp when you are allowed to use them for your own/personal car) it took close to 60L (59.6L) and the TC was saying it had used 62L
i was happy with that varience as it wasnt out that much, and around town back on the gold coast, it matches within 1 or 2L what the TC says - pump literage was close enough to be good enough.

the trip was mostly 100 - with 110 on pacific highway from nerang to logan - then over the gateway to a crawl to get out of town (well it was a good run actually) and then the 100km/hr limit up until marlborough where its 110 for a hundred of so kays.
its relatively flat really considering.

car had me n bf in it, plus a few other things - would have been carrying no more than 200kg in people and goods.
Climate control set at a comfortable 22 degrees the whole way here.

drove up to mackay from the gold cost, and used / put in TWO full tanks to get here.
so thats 71L x 2 tanks = 142L right?


Wouldn't this be assuming that you only filled up when you had completely run out of petrol (i.e stalled and would not start)?

My Trip computer is very accurate, If it says I've used 20 Litres, Than when I fill up, The pump is usually within .5 of a litre, I avg 8.1 L/100k on a highway trip averaging around that 85kph

Wouldn't this be assuming that you only filled up when you had completely run out of petrol (i.e stalled and would not start)?

thats true yes.
i was more referring to the fact that i had filled to capacity the tank twice.

i was working on two full tanks of 71L - and yes i had not run out of fuel completely.
i was more worried i guess by the fact that i was running around with only 3L sitting in the bottom of my tank - no matter how broke i/we are, i will never let the car run that low on fuel.

Trip computer accuracy vary in some degree from car to car, it will change with the age of the car as well. On my car it will show 50 litres used, but servo bowser will show 55 litres when I fill it. It used to be more accurate 5-6 years ago, anywhere between 0.5-1.5 litre.
Generally trip computer will display estimated fuel used or distance traveled and should be taken as a guide only. It is not 100% accurate as someone may think.

To check accuracy of the trip computer next time you fill the tank fill it full and reset trip comp. to zero. Also reset your tripmeter to 0000. After a few hundred km, when filling tank again fill it full and record how many litres you poured in it. Record what your trip comp displays eg. total fuel used, total distance travelled, average fuel consumption. Also record km your tripmeter shows.
Now you can compare the numbers and see if there is any difference. If it happens that trip comp. shows less fuel used than the pump at the servo, it will also give you an inaccurate (lower) average fuel consumption figure and vice versa.

I believe AWD magna's plastic fuel tank capacity is 70 litres.

doddski, after reading your first post again I got better idea what's bothering you.
Trip computer will display total fuel used in litres of course. It will display range to empty in kilometres, that is estimated distance in kms that can be driven on the remaining fuel in the tank. It will never tell you how many litres is left in the tank.

NOTE:The range data is automatically adjusted at fuel refills. The system will only detect a fuel refill under the following conditions:
(1) The refuel is more than 15 litres.
(2) The ignition is in the "OFF" position when vehicle is being refilled.

Trip computer doesn't add up litres each time you refill. It gets signal from fuel gauge assembly which is inside fuel tank about amount of fuel inside the tank and estimates range to empty.
Estimated range to empty is based on average driving conditions and how you have been driving. It is gradually modified as you drive. An abrupt change in driving style results in a gradual change of estimated range to empty. Since actual range available depends on how you will be driving (speed, gradients, etc.) the indicated range to empty should be used only as a guide.

Until you have your fuel gauge sorted, I suggest you rather relay on Range To Empty function than on Total Fuel Used.
The display will show "---" flashing when the range to empty is less than 50 kilometres.
On the other hand when refueling fill the tank full and reset trip computer afterwards and go with the Total Fuel Used.

I believe AWD magna's plastic fuel tank capacity is 70 litres.

the handbook says its a 71L tank...

on the way back to the gold coast, i will being doing what you suggest and record everything - L on TC used VS L on the pump, and over the corse of a month or so il be able to see a trend developing.

whenever i fill the car right up, i always reset all meters, L used, Dist travelled etc all back to zero to see what econ i get out of that tank of fuel for that week/period till next fill.

il only do that on fill right ups - never on the $20 top ups etc, coz that just makes things too complicated.

christmas sucks too - families are really annoying, esp when they are the bf's laaaarge family... but oh wells, at least it only comes once a year! lols!

EDIT - i have been able to drive an additional 150 - 200km when the display is flashing "---" at me and to fill it, only took 50ish Litres to fill it..
that was before the car went back the FIRST time to get the tank sender replaced - after that the accuracy of both the DTE and L used seemed to have increased a fair bit, but im still not happy that it is even close to where it should be.
i know the needle and the tc readouts are an estimate only, but i would have thought that the estimates would have been a lot closer.

when i get home to the coast, we will be checking the O2 sensor, and replacing if required, and see how we go from there.
also when it gets its service, will be telling them to look at the fuel prob AGAIN - and bill the dealer here in mackay for the work and it was reported in the stat used car warrenty and has to be honored for life if there is still an issue with it.

mine is a little out, i have my trip computer say i have used about 64L of fuel and when i filled up about 60L went in, but i choose to follow the trip computer as i then think i haven't got too much left and should fill up instead of running it any lower than i should be...

i have been able to drive an additional 150 - 200km when the display is flashing "---" at me and to fill it, only took 50ish Litres to fill it..

Yeah I have found the DTE to be pretty rubbish, as you said 50L used and it starts flashing. Litres used is usually less than 2L off, and average is pretty much spot on.

Does your fuel gauge read properly? Honestly I have no faith in it, seems to just show a random amount each time I start the car :P Litres used on the trip computer is my gauge, and it's pretty close.

i thought i read it in the owner's manual that the fuel warning light comes on when approx. 80% of fuel has been used so 80% of 71L would be about 56.8L. please correct me if i'm wrong. i don't really read the manual, i just skim it...

from my experience with fuel lights in most cars, they usually come on with approx 8-10L left in the tank.

as for the missing fuel, there is always the chance that someone syphoned some fuel out of the car during the night if it was parked somewhere accessable. just because the filler was closed and the cap back on doesn't mean it wasn't done. some people are just smart enough to make it look less obvious it was done.

Does your fuel gauge read properly? Honestly I have no faith in it, seems to just show a random amount each time I start the car :P Litres used on the trip computer is my gauge, and it's pretty close.

my fuel guage is out by a lot.
drops slowly to 1/4 used, then suddenly its dropped to the 3/4 used mark - in what feels like a matter of seconds!

from there, it just drops - i have seen it bounce back up to 1/2 as well on more than one occasion..


on the way back from mackay, the fuel used as within 5L(5L out was only once) at each top up on the way back - but i always put extra in than the readout said i should have needed. but i can handle a max of 5L variences.
we wernt filling the tank at each stage either - just a few 30 / 40 dollar topups and that got us home.
with an average of 10.5L / 100km along the way...
but we came a different way home and had to do a little driving through some ranges.

also - silly question (arnt all mine silly!)
but

the shape of the tank in the sedan, appears to be across the tailshaft / exhaust tunnel.
in a (crude drawing but still)

[__/ \__]

where the little / \ symbolise the hump for the tailshaft.
when the fuel gets low enough so that there are now 2 halfs in theory, does the fuel guage ass'y take its reading from both sides.. or one?
reason i ask, is sometimes it wont take more than 20L when i know it needs at least 40L... and if i rock the car side to side a few times... i can get the extra in.

is it just me that thinks like that? lol

cheers!

that is a good point. i wonder if the gauge would be reading both sides of the split tank or just one. and also is the other half even useful. does the fuel pump pump out of both halves???
who knows?

It would have to be reading both sides of the tank surely. They couldn't send out the car not reading the tank properly.

It would have to be reading both sides of the tank surely. They couldn't send out the car not reading the tank properly.

haha one would assume so, but you never know these days. car dealers and manufacturers - its all about the bottom line!

i just looked at my workshop manual (since i'm at work and i can't just go look at the car) and the pic seems to show that it doesn't really have 2 low sections. the exhaust goes around it, but it does have a flat spot on 1 side

i just looked at my workshop manual (since i'm at work and i can't just go look at the car) and the pic seems to show that it doesn't really have 2 low sections. the exhaust goes around it, but it does have a flat spot on 1 side

ah ha the plot thickens. that makes more sense.

so one would then further assume the the sensor is in the deep part of the tank?

ah ha the plot thickens. that makes more sense.

so one would then further assume the the sensor is in the deep part of the tank?

i would hopeso - along with the fuel pump to get the juice up to the injectors.


also - a few posts ago, someone said that the fuel light comes on when you have used approx 80% of the fuel;
is that 80% of a FULL TANK of fuel, or 80% of whatever you just put into the tank.
(ie - have 10L LEFT, ADD 10L, so will the light come on at approx 4L Remaining?)

i miss the days of old, when it was all set and and forget stuff.
in my LTD, when the fuel light comes on, i know that i only have 10L (of an 80L tank mind you..) left - which works out at most to be 30 - 50km of driving...

Well mine comes on around 20L, and I'm pretty sure it doesn't matter if it was a topup or a full tank.

Well mine comes on around 20L, and I'm pretty sure it doesn't matter if it was a topup or a full tank.

reason i asked, was because sometimes the light hasnt come on for a while on a small topup (from light allready on) and others it comes on straight away / doesnt go off.

i know it wants more than 15L for it to register straight away for the needle to move, or 20mins in the key off possition.

i still need to get my guage sorted out properly (for the third time...) and im hoping that when that happens, my guage will be right :)

The red light for low fuel will come on with approx 8 - 10 L remaining in the tank (i squeezed 110kms out of her once hahah) as MitchellO said :)

doddski your sender unit is prob rooted a friend of mine had a 00 VRX and went thru 3 of them, luckily i havent had a single prob *touch wood*

Cheers mate

Heath

The red light for low fuel will come on with approx 8 - 10 L remaining in the tank (i squeezed 110kms out of her once hahah) as MitchellO said :)

I'm not sure how far I have driven with the light on, but one time it was quite a fair distance. Had a couple of mates in the car who were a bit nervous :P Took 68L when I filled lol

Fuel tank in AWD is a saddle type to allow for the tail shaft.
There is a fuel transfer suction hose which is connected to the jet pump, together with fuel return line. It transfers fuel across the hump into the side where fuel gauge/pump assembly unit is.

Doddski I believe that o2 sensor is quite ok. It is your fuel gauge that gives you inaccurate readings. By the way 10.5 and 9.8 l/100 km average is not bad for AWD with air con, luggage and that hairy, nasty holden guy lol in the passenger seat.
Also, fuel light will come on at about 80-85% of a full tank used.

mad 082 magna, FWD have different fuel tank than AWD.

From the workshop manual for the KL AWD

http://img80.imageshack.us/img80/7190/picture3wc5.png

i cant believe you are going on with all this on 9.8L/100 if i got that, my face would hurt from smiling. Pam and i took the TJ sports down to Wollongong and back a couple of weeks ago and the best we got it down to was 10.8 and that was over 540km.

In an AWD verada at that, i'd be happy with 9.8.

mad 082 magna, FWD have different fuel tank than AWD.
yeah i realise that. if i was on the other computer i would post up a pic of the fwd tank for everyone.


reason i asked, was because sometimes the light hasnt come on for a while on a small topup (from light allready on) and others it comes on straight away / doesnt go off.

i know it wants more than 15L for it to register straight away for the needle to move, or 20mins in the key off possition.

i still need to get my guage sorted out properly (for the third time...) and im hoping that when that happens, my guage will be right :)
the fuel light is triggered by a simple on off system. while it is submerged the light is off and when it isn't the light comes on. that is why you may find the light come on when you are going up a hill or something then have it go off once you get back onto level ground and the guage hasn't moved. i know that in the missus pulsar once it gets below about 1/4 of a tank the light will come on whenever you go up a steep hill and go off once it starts to level out and you can get all the way down to the empty line before the light comes on and stays on.

yeah i realise that. if i was on the other computer i would post up a pic of the fwd tank for everyone.

http://img80.imageshack.us/img80/2576/picture4oa9.png