Hi guys, I recently bought a generic OBD-II scanner from eBay to see if I could diagnose the increased fuel usage after my last tune-up service. I've been experiencing an average of 18L/100KM and I'm out of ideas as to what may be causing it. I had my muffler welded as it exploded, and all oils are OK except for the engine oil which I plan to empty and replace.

As far as I know this car may have been one of those used-and-abused cars before I bought it so I'm not exactly sure what factors can cause it to be using so much fuel. I always put in at least 30L of 98 Vortex so it can't be an issue of fuel. If you guys know of anything that may go wrong regarding the fuel please spam me as much as possible.

Regarding the OBD-II scanner, I can't seem to find the port. I assume it's under the driver's footwell but I just can't find it to save my life. Is it actually located in the footwell or is it hidden with the engine bay?

Thanks for the help, I really appreciate it!

You won't TJ does not have ODB only MUT

If only the Third Gen Magnas had a standard OBD2 port . . . alas, it doesn't.
You can read error codes easily though, do a search.

A good OBD2 implementation on a car and a good scanner will tell you lots, right down to which spark plug is misfiring and which oxygen sensor is slow to respond, but unfortunately the MUT system in the third gen isn't that sophisticated, so even if you get no error codes, there may still be a problem with the cat, oxygen sensor, etc.

To test your fuel consumption for problems, warm the engine up and get instantaneous consumption for steady speeds at 60, 80, 100 (on appropriate roads of course) and we can tell you if they are normal or over the top.

My TJ can get up to 16.6L/100Km on very short trips in cold weather though. Best I've seen is 7.7 on a 300 km long, sedate warm weather country drive.

I've been keeping a steady average which has ranged between 16-18L/100KM. My instants for 60KM were about 17-20L/100KM, 80 was about 10L/100KM and I haven't had the chance to go at 100 (how I wish to do that one day).

Not sure if that's a normal range, I feel like it's still a bit high but perhaps I may need to granny drive it to get something that low. Thanks for the help so far, I'll keep collecting data while I wait for more responses.

A mate's KJ was doing this, it's the O2 sensor.

Sorry to bump an old thread, but after changing the O2 sensor, the fuel averages are still roughly the same. I've investigated and I was suggested to change the fuel sender.
Is there any significance of that module in regards to higher or lower fuel usage? I'm constantly granny driving the thing but I find that it uses more fuel that way.
Would it also be possible the ECU needs a reset?

Sorry to bump an old thread, but after changing the O2 sensor, the fuel averages are still roughly the same. I've investigated and I was suggested to change the fuel sender.
Is there any significance of that module in regards to higher or lower fuel usage? I'm constantly granny driving the thing but I find that it uses more fuel that way.
Would it also be possible the ECU needs a reset?

Dumb question...you have gone thru the startup programming and ensured it is it to the specific engine and shape of your vehicle? 3 or 3.5 sedan or wagon?

Second dumb question...do the numbers on your screen match the number at the bowser...ie screen say used fuel = 25 Litres (example) refill at servo -= 25 litres?

I suggest you check your ignition system - ie the spark plugs (how old are they? if old, buy some new iridiums-they have a very fine point giving a better spark), the leads (is the resistance within specifications? the front back should be easy to check - if they are bad it may be worth removing the plenum to check the rear as well) and the distributor (is the cap cracked? check the metal contacts inside the cap - they can have a build up of oxidation that needs to be scraped off (I cleaned mine and got a noticeable improvement in economy)).

Sorry to bump an old thread, but after changing the O2 sensor, the fuel averages are still roughly the same. I've investigated and I was suggested to change the fuel sender.
Is there any significance of that module in regards to higher or lower fuel usage? I'm constantly granny driving the thing but I find that it uses more fuel that way.
Would it also be possible the ECU needs a reset?
If the ECU wasn't reset when the oxygen sensor was replaced, it will eventually re-establish good fuel trims but it takes a bit of time - 10-15 minutes of idle plus anything from 30 mins to a couple of hours of actual driving. Resetting the ECU (by disconnecting the battery for a few seconds) hastens this process somewhat.

The engine temperature is a factor as well. If the thermostat is stuck open and you do lots of shortish trips, then the engine is effectively running with the choke on.
I recently did a high fuel consumption ford focus and the thermostat was fully open at 55 degrees C. The spec says fully open by 95 degrees. Replacing the thermo fixed the problem. The car now reaches normal temperature in 5 ks of travel. It was using 10 to 11 L/100 K on a run, but now is 7.7. The second oxygen sensor had been diagnosed and changed previously, but it made no difference until the thermostat was changed. I think the second oxygen sensor was actually OK. It was however, caked with carbon buildup.
Hope this helps.