Is tune up needed in toyota altis 2002? gas consumption has gone up to 6 kms. per liter

the fuel consumption figure is what mazda get in a factory controlled test operation and is only an indication of what can be expected with careful driving
they have no control over driving habits or traffic conditions and drive speeds as the variation is too great to even talk about
by the calculations you are getting 5.6 liters per 100 klms so where is the problem
to get exact figures for your driving habits
you go from tank full to tank full and divide that into the figure set on the trip meter when filled the first tank, not what you have calcuated

best at 10 liters per 100 klms , average around 12 liters /100 klms
fuel consumption depends largely on load , speed , operating conditions , towing, highway/city, off road so an exacting answer is not possible as it all depends on the operator and the driving skills

20/25 mpg for city/highway is the same as 8.5/10.6 kms./liter city/highway. I hope this is what you needed.

10 litres per 100 klm Could be slightly better on a long run. These cars are considered good on fuel for a medium / large car

the factory mileage for fuel should be 7.2 litres per 100km but the fuel consumption will change as the car gets older so its only normal but you could improve on your fuel consumption by tuning the car

hope this helps XD

Obvious things first. replace your air cleaner, fuel filter and put in a good quality fuel injection cleaner. do this for at least two fuel tank loads. Clean the injectors and make sure your engine is tuned. It will be fine after that...

if this car has more than 100,000 miles, try switching the motor oil to a "high mileage" formula oil. this can reduce oil leakage, and reduce oil burnoff.

I see this a few days old now,my carbed 22r is getting about 18-19 mpg on 31" tires,or about 340 to a tank,so you should get about 540 kms off a tank bearing in mind my tank holds 18.6 gallons or 70 liters.Definitely something wrong with the truck,how does the truck run good power?is it auto or manual?

it can be some reasons mybe cylinder head, inlet valve worn out.
it can be cuporator valve releasing more petrol into the inlet.
Brakes it can be. check contacpoint.