Poor Economy

[jonmac]

My 2004 VY ute is on dual fuel and gives, what I feel is poor ecocomy, 15l/100km and 22/100 when towing. I've had this problem since I bought it. I've replaced plugs and filters, ensured tyre pressures are right etc. I have the gas part checked and calibrated at every service. My only other thought is, could it be in the auto transmission? It only goes into overdrive at 125kmph. Any other things to consider??

[m1lky]

Is the tranny in economy mode? In power they don't like going into lockup.

Take it it's a 6? How heavy was the towing when you got 22?

15 sounds a bit high, but what sort of driving do you do?

My vy ss trip computer is pretty pesimistic, usually about 1-2 over if you work it out on ks done and litres to fill

[White Tiger]

have you checked you O2 sensors
because they measure the air/fuel ratio
and if they are buggered they will make the car think its running lean
so it will inject more fuel to get it back to the right mixture
or something like that

Edit: and that ^^^^^^^

[Burnout124]

15 is about normal if you have a draw through system. if you have vapor injection it can be less about 13L/100

[jonmac]

Yeah, Its a six, and its in economy mode. Could it possibly be in the computer program, that's not letting it drop into top? In regards to driving, it only goes out of town on irregular trips up to 600km, but uses all the gas (56l) and most of the petrol just to do that amount of km's. When towing, it has a 1900kg pop-top van

[jonmac]

Where would I find the o2 sensors???

[D3CID3R]

on the exhaust pipes just infront of the gearbox sump

[D3CID3R]

HOPE THIS HELPS

[b3h3m07h]

15L/100Km sounds about right for a venturi system. back when i had a vp v6 and a vr v6 i was getting around 15-17L/100km with a combination of city and country driving. I did how ever have a big fuel consumption issue when i first bought the vp. Its best economy was only around 21l/100 but the culprit turned out to be the oxygen sensor, replaced that and fuel economy jumped to around 15l/100. Also a mates ef falcon on gas which also gets around 15l/100 said that when towing he noticed a drop in economy, he said that when towing around a tonne his best econ was about 22l/100 like in your situation. no doubt when towing more fuel is used but depending on the aerodynamics of the trailer, wheels and weight this will vary. Also what rev's are you sitting on when cruising at 100 / 110km/h, is it around 1700 to 2000rpm or higher?, mine sits around the 1800-2000rpm mark on a flat stretch in overdrive.

[jonmac]

Thanks to all who replied. Firstly I will get the 02 sensors checked asap. In response to b3h[v]07h, at 100kmph the revs are at 2500. As I stated in my first question, it only gets th 2000rpm at 125-130kmph; could it be in the transmisiion or in the computer chip that manages the trans??

[som]

yes.i have a VT that used to change into 4th @78kph which used to really tick me off when driving in an 80kph zone because the gearbox was constantly changing gears.i know nothing about chips or how adjustments are done but i left it with my mechanic for a couple of hours who said that he'd altered the ??? and now it changes @73kph.re towing-i frequently tow a 4.6m boat behind my car,often on long trips (brisbane to darwin once a year)and my highway fuel economy drops from 8lp100k to 14lp100k.in 4th gear @2000rpm i'm travelling @112kph

[TMM]

yes.i have a VT that used to change into 4th @78kph which used to really tick me off when driving in an 80kph zone because the gearbox was constantly changing gears.i know nothing about chips or how adjustments are done but i left it with my mechanic for a couple of hours who said that he'd altered the ??? and now it changes @73kph.

Probably just reset the computer by unplugging the battery.
The computer that controls the transmission has a learning capability - if you drive it like you stole it, all the shift points get pushed up (holds gears longer, lets it rev higher). Similarly if you drive like a granny, it retards all the shift points.

When you unplug the battery the computer forgets everything it has 'learnt', resets to the base shift map and relearns your driving style. The same method works if you get a dodgy batch of fuel and it pulls a heap of ignition timing out of the engine, when you get some better fuel in there you can just pull the battery which will reset it to a base timing, and from there it'll learn the timing it should be running by listening to the knock sensor.

The two things it looks at to decide what gear to be in are the throttle position sensor and the speed. I guess you could also alter the shift points by playing with the throttle position sensor.

[monkeys437]

at 100kmph the revs are at 2500.

Does that seem a little high to anyone else? You should be doing 140kph at those rev's. Do you have 4.11 gears or something?

[m1lky]

Not in top gear or lockup?