Need help please !!!

[tiersum]

Vs commodore 73,000km

My fuel economy is shocking 300km out of 50L no aircon driving like a granpar. 98 vortex
My brakes arent dragging the fuel filter is recent , injectors were cleaned about 15,000km ago , maf throttle and air filter are cleaned regularaly. the power is fine i dont have a loss. I have a high flow cat and exhaust system no indications its blocked my oxy sensors were replaced 9months ago no faults im stumped please help

[r_i_d_a_h]

ive got the exact same problem..though i havent had the time to sus it out.

I suspect ive got a leak from the fuel tank and/or possibly a buggered breather hose.

take i look under your car and look at the tank to see if it looks like somethings been leaking and left a marking.

[tiersum]

just checked nothing out of the ordinary ive installled a replacement memcal tuned by someone and the car chews more fuel car was managing about 350 before changed the memcal now it does 300 the car use to do 400km around thecity

[WAFFEN SS]

Mine did the same and ive tryed a few (off the shelf) memcals and there all shit. go spend the money on a dyno if you realy wana make it pull like a school boy, I did mine after putting a sc14 charger on and now all is well and get 450-500km on a tank of gas.

[bandit10]

Try fitting a new temp sensor.
I get 400kms to 45-50ltrs out of my 5ltr round town

[shifty6]

as said its very likely your coolant temp sensor.
if its an aftermarket chip tho it could just be a very crap / rich tune.

[hako]

just checked nothing out of the ordinary ive installled a replacement memcal tuned by someone and the car chews more fuel car was managing about 350 before changed the memcal now it does 300 the car use to do 400km around thecity

I think you've answered your question yourself!....put the original memcal in and it will go back to 350km which is halfway back to your 400km. With the original memcal replaced you'll also be able to use 91 ron fuel and save 15c a litre.