Poor fuel economy - 6L manual

[exanVZ]

Hey guys,

My cars been at the smash repairer for about 6 months and just got it back 2 weeks ago. First thing I noticed is that the fuel economy seems to be much worse than it was before. I mostly just drive to work but it's a mix of stop start traffic and highway traffic, probably 65% city / 35% freeway traffic. Currently getting 20.5L/100km, average speed 38kph, over the last 350km since I reset the trip counter and it has slowly come down from 21-22L/100km but not by much. This is running on only 98 fuel also. I'm not expecting miracles but usually I feel like I should be getting more like 14-17L/100km. Car has basic mods, OTR CAI, mafless tune, headers, cats, 3" exhaust.

Thought it might be old fuel sitting in the tank so I drove it until it literally ran out and then filled it up about 1/3 of a tank a few times to flush out any bad fuel. Hasn't made much difference. Next I'm thinking of replacing the air filter and spark plugs, the filter is probably 7 years old and not sure how old the plugs are. Maybe fuel filter too. Any other suggestions on what to look at?

What kind of economy do others get? I know V8's aren't the best but usually don't see anywhere near 20L/100km unless thrashing it.

 

[keith reed]

Our VE is little more than a shopping trolley and I can't remember when it last had a decent run. I just checked and at an average speed of 34.5 k's fuel consumption is 16.2.

 

[exanVZ]

Our VE is little more than a shopping trolley and I can't remember when it last had a decent run. I just checked and at an average speed of 34.5 k's fuel consumption is 16.2.

thanks, that's more what I remember getting so something seems a bit off with current fuel consumption.

 

[exanVZ]

Changed plugs and air filter, done about 150km since then and mixed driving, no super heavy traffic. Fuel economy still sitting about 19-20L/100km. Slight improvement by about 2L but not as low as I think it should be. Not driving it hard, just normal driving to work etc. Tyre pressure also is fine btw, checked it and all 4 are at about 38psi.

It did just get a brand new full exhaust under insurance about 700km ago, could a new exhaust not worn in cause higher fuel consumption? Any other suggestions?

 

[losh1971]

Don't go by the trip computer it's not an accurate enough method of gauging mileage. The most accurate way to test is fill the tank to the top of the neck and drive 100km or 200km. Fill again to the top of the neck and repeat. Do that twice so you can get a good average across your driving and then see how much petrol it takes each time to fill it back up both times.

 

[exanVZ]

Don't go by the trip computer it's not an accurate enough method of gauging mileage. The most accurate way to test is fill the tank to the top of the neck and drive 100km or 200km. Fill again to the top of the neck and repeat. Do that twice so you can get a good average across your driving and then see how much petrol it takes each time to fill it back up both times.

Will give that a try. Filled up a full tank tonight as it was cheap and the tank was almost empty, only took 55L despite distance to empty being about 10km. I think it's a 70L tank, so seems the computer might not actually be so trustworthy. I'll try as you suggested over the next week or two and see how it goes, cheers.

Running 98 fuel and conservative driving and no cam I would expect about 14-16L/100km approx.

Also considering swapping diff gears at some point in the near future which I feel might help too. Might try and go up to 3.9 gears but probably not 4.11.

 

[07GTS]

maby one or both of the fuel senders are wearing out, once they start to play up they will read lower then actual which could explain the 55L to fill up if it were showing empty, this also throws out the trip calculations, look at your liters used as that should be very accurate and compare to the liters u get in the tank when filling

 

[exanVZ]

maby one or both of the fuel senders are wearing out, once they start to play up they will read lower then actual which could explain the 55L to fill up if it were showing empty, this also throws out the trip calculations, look at your liters used as that should be very accurate and compare to the liters u get in the tank when filling

Thanks mate, didn't know that could affect it, I will measure it old school for a few weeks and see how it looks.

 

[Fu Manchu]

V6

I wouldn’t feel too bad.

 

[keith reed]

V6
View attachment 259985
View attachment 259986

I wouldn’t feel too bad.

Bit less average speed and a bit more average fuel than my Redline.