Massive fuel issues, possibly caused by flat battery?

[sparky0916]

Hey guys,
I have an '00 WH statesman (5.7) that is having some massive issues... I had a flat battery last week after not driving it for a week or so, we had to jump start it two days in a row but now the battery seems absolutely fine. Ever since, the fuel economy has been pretty ordinary, but yesterday it became a big issue when under the lightest acceleration from a standing start the fuel usage has started jumping up to 80l/100km! it doesn't have any visible signs or odor of fuel leaking, it isn't running any rougher than usual (it's almost due for a service and needs a bit of oil, etc), doesn't feel sluggish or restricted in anyway, but i watched a 1/4 tank of fuel, disappear in minutes during light city driving! it's fuel use at idling is 2 or 3 times higher than usual, under light acceleration from traffic lights, etc it goes up to 70-80l/100km and then eventually drops back down to about 20l/100km (give or take) when doing 60km/h in 'D' on a flat piece of road...

Has this happened to anyone else, or does anyone have any ideas on what might be causing it?
Thanks,
Sparky

 

[sparky0916]

Scrap the bit where I said the battery seems fine now... Alarm just went off so I went out to check it and the battery had gone flat in the last 6 hours

 

[Tasmaniak]

Your fuel consumption sounds completly normal to be honest. My old LS1 was similar, my V6 does the same thing... hell even, the 4cyl can do it as well.

If it really drank 1/4 tank in minutes through the city then it will be belching black/brown smoke and you won't be able to stand behind the car without falling asleep due to hydrocarbons being pumped out. After a flat battery it's not uncommon for the computer to reset itself and use a bit more petrol than usual. Infact, my LS1 wouldn't not actually idle at all after jump starting. You had to hold the RPMs at about 1,000rpm for the first couple of minutes before it would stay running by itself.

have your battery and alternator checked before replacing either.