Over the past few weeks the fuel consumption has steadily increased from mid 11/100km to the point where today it went to 13.1 l/100km. I have never seen 13 before. I do all maintenance myself and plugs, airfilter, fuel filer etc all good. It is 2002 3.5 Tj auto sedan. Any ideas anyone.

Oxygen sensor.

could also be a leak in the exhaust pre oxygen sensor

does it feel rough or do you smell fuel???

Just for ideas, could a collapsing / blocked cat converter cause this ?

Could be nothing at all . . .

Short trips, lots of cold starts will do it, cold idling in your driveway or at traffic lights, etc.

My 2001 TJ is sitting on 13.8 at the moment. I can get it up past 15 easy, just short trips and 3 or 4 cold starts during the day.

In summer, with 20 Km + trips, it gets 9.5 or so.

But feel free to worry about O2 sensor, MAF, collapsed CAT, value of the AU $, etc. lol

Warm it up, go somewhere you can do a steady 80 KPH, and look at your instant fuel consumption. A much better indication of problems, if any.