Hi guys. My TJ has been running pretty well for the past year, although I have noticed that at times the fuel consumption just goes through the roof. Usually it sits at around 13l/100km with Premium and 14l/100km on normal unleaded. However twice in the past 6 months it has risen to just under 16l/100km with Premium and that is with me trying to be as gentle as possible with driving. It is making me nuts.

The common thread amongst this however is the fact that the car was due for a service then and is again now. I have noticed that the more Ks you do over 7500km between services, the worse the fuel economy becomes. After a service last time, it took a couple of weeks, but the fuel consumption returned to normal.

Is this common? Could there be something specific causing this?

seems extremely strange, my fuel economy is around 10-11L/110k (manual 3.5L) but it has also had a tune for 98

How is your 02 sensor? Not necessarily recomending changing it, but has it been changed recently?

It hasn't been changed since we bought the car which was just over 2 years ago.

What would that cost to replace if required?

Hi Trido,

I bought mine from here. Received it 2 days after purchasing, however am yet to fit it.

http://www.cyberspaceautoparts.com.au/contents/en-uk/p82.html

That's not too expensive. So, I am rather ignorant of mechanical stuff. :P What does the 02 Sensor do, and how could it affect fuel consumption? Is it not mixing the fuel with enough air before going into the engine and thus pushing in more fuel?

During the last service, I asked our mechanic about the fuel consumption issue and he did a test of the exhaust emissions, but they came out normal. Not sure if that changes anything.

To be honest, not entirely sure.

What I do know, is that my car has done 200,XXX kms and still has the original O2 sensor and suffers from very poor fuel economy (similar to yours) despite doing some basic servicing (plugs, leads, fuel filter..etc).

And at $115, it's a pretty cheap part they may fix my problem and is worth a shot.

correct me if i'm wrong but o2 sensor controls revs.. so if not working your car will rev higher.. i think that's what happened to my TE a while back.. rev's were sitting at 2300 all the time and it could literally drive itself.. it was a manual and i couldn't slow down with engine, had to always use brakes. at lights it would rev up to 2300 and people would think i was edging them on. once i got o2 sensor changed, it was all fixed.

correct me if i'm wrong but o2 sensor controls revs.. so if not working your car will rev higher.. i think that's what happened to my TE a while back.. rev's were sitting at 2300 all the time and it could literally drive itself.. it was a manual and i couldn't slow down with engine, had to always use brakes. at lights it would rev up to 2300 and people would think i was edging them on. once i got o2 sensor changed, it was all fixed.

no it monitors fuel mixtures after the burn whether its running rich or lean

Correct, "o2 sensor" = oxygen sensor. Things that control your revs at idle is your ISC (Idle Speed Control) motor in your TB.
Only thing a crappy oxy sensor will do is give false readings (element gets clogged up over time) and thus result in poor fuel consumption.
Other things to check are your basic service items, air filter, fuel filter, leads, plugs, if left to deteriorate for ages it'll all contribute to crap fuel consumption, but mainly o2 controls your mixtures.

Also change your coolant temp sender or get it verified. If the coolant sensor reads cold when warm it'll be dumping in heaps of extra fuel to help "warm" the car up when in fact it's already warm.

Sure must be something wrong, Oxygen sensor or something else, as I'm averaging 10.4l/100km after the manual conversion on my 3.5 - & that's with a fair bit of city driving.

You can take a resistance measurement with a multimeter and compare them to readings to factory specs.

It hasn't been changed since we bought the car which was just over 2 years ago.
Afaik the oxygen sensor isn't a service item, so it probably hasn't been changed. They normally seem to give out around the 100,000km mark. On my TJ VR-X it was beginning to give out at about 110,000km.

Dude 14l/100k is alot!! i get around 10.5l/100k in town and down to 7-8l/100km on the highway. 3.5l Auto 4spd

Mine is always around 14l/100 at the moment but it's usually worse for wear from the 5 minute drive to the train station each morning.

have to say our VR-X is usually between 11.4 - 12.0L/100 and thats with travelling 22k's each way morning and night.
as far as i can remember havnt changed the oxygen sensor yet but i know that about 95,000 kms the idle was playing up all the time when stationary turned out was the fuel injectors needed a clean even tho we use the fuel system cleaner on regular occasions..
the other night i drove it prob about 60km round trip and cost me about 10litres thats cos i was excited to drive it...
when i had my VS Calais had that modified and was using about 13.5 - 14.4L/100 after was tuned so im kinda used to high fuel bills...

Hmm, even on a good day my car seems to drink more fuel and I am not an overly aggressive driver. When we first got the car it did 7.7km on its first highway trip but I've never got near that since. Best is around 9.0l/100km. Usually sits around 9-9.5. Town driving has never been better than 12.5 which is again, when we first got the car. It stayed around that until we did our first fill up after a couple of weeks and then started to rise.

I know traffic does have a lot to do with it. I drive through numerous roundabouts and lights on the way to and from work (14km round trip). I always attributed it to that.

Also, my car is the 5sp Tippy, would that make a difference either way to fuel consumption over the 4sp auto or the manual?

Would the fuel filter make a difference to fuel consumption? The car is being serviced today and apparently the fuel filter was in need of replacing.

i have a 5 sp tippy and instant readout gives 12.0 city and average, goes down to 10.5 on longer trips, i.e. from melb to philip island (200kms). i drive a mixture of agressive to granma depending on traffic conditions and urgency..

i have a 5 sp tippy and instant readout gives 12.0 city and average, goes down to 10.5 on longer trips, i.e. from melb to philip island (200kms). i drive a mixture of agressive to granma depending on traffic conditions and urgency..

Sounds almost identical to me.

i get around 11l-12l/100km local driving and even down to 7-8l/100km on the open road in my VRX. Oxygen Sensor was replaced at 100k.
Hope it sorts the guzzling problem though.

Hmm, even on a good day my car seems to drink more fuel and I am not an overly aggressive driver. When we first got the car it did 7.7km on its first highway trip but I've never got near that since. Best is around 9.0l/100km. Usually sits around 9-9.5. Town driving has never been better than 12.5 which is again, when we first got the car. It stayed around that until we did our first fill up after a couple of weeks and then started to rise.

I know traffic does have a lot to do with it. I drive through numerous roundabouts and lights on the way to and from work (14km round trip). I always attributed it to that.

Also, my car is the 5sp Tippy, would that make a difference either way to fuel consumption over the 4sp auto or the manual?

Would the fuel filter make a difference to fuel consumption? The car is being serviced today and apparently the fuel filter was in need of replacing.

4sp auto and a 5sp manual are worlds apart in terms of power to the ground and fuel economy.
5sp tippy and 5sp manual are almost neck and neck when it comes to power to the ground and fuel consumption.
Start stop traffic will ALWAYS kill fuel economy.

;1219366']Correct, "o2 sensor" = oxygen sensor. Things that control your revs at idle is your ISC (Idle Speed Control) motor in your TB.
Only thing a crappy oxy sensor will do is give false readings (element gets clogged up over time) and thus result in poor fuel consumption.
Other things to check are your basic service items, air filter, fuel filter, leads, plugs, if left to deteriorate for ages it'll all contribute to crap fuel consumption, but mainly o2 controls your mixtures.

Also change your coolant temp sender or get it verified. If the coolant sensor reads cold when warm it'll be dumping in heaps of extra fuel to help "warm" the car up when in fact it's already warm.

my car now doing 17.x L/100km city driving and about 14.x L/100km on country road. I know she is very thirsty now.:beer:. but the coolant sensor seems working fine as the needle of the temperature gauge pointing within normal temperature range (half way of the gauge). so does this mean I can cross out the possibility of the coolant temperature sensor fail? my car has 4sp tippy and 160k on the clock.

If I decide to get a new o2 sensor to put on, should I get the mitsu genuine one or aftermarket would have better performance?

thanks for your advices
cheers
Kelvin

When people say city driving, do they mean stop start in the CBD in peak hour?

I kinda doubt it... I'm going out on a limb and saying suburban driving.

It's impossible to get a fuel consumption of 11l to the 100k or whatever when you're idling for 20 minutes, crawling stop start for 40, which = an hour trip that usually takes you 20.

Impossible in a Magna.

my car now doing 17.x L/100km city driving and about 14.x L/100km on country road. I know she is very thirsty now.:beer:. but the coolant sensor seems working fine as the needle of the temperature gauge pointing within normal temperature range (half way of the gauge). so does this mean I can cross out the possibility of the coolant temperature sensor fail? my car has 4sp tippy and 160k on the clock.

If I decide to get a new o2 sensor to put on, should I get the mitsu genuine one or aftermarket would have better performance?

thanks for your advices
cheers
Kelvin

the aftermarket ones are cheaper and do the same job, you can get a plug and play one from ebay fro around $110.You can get one with out the plug on it for around $80 and you will have to solder it on your self

my car now doing 17.x L/100km city driving and about 14.x L/100km on country road. I know she is very thirsty now.:beer:. but the coolant sensor seems working fine as the needle of the temperature gauge pointing within normal temperature range (half way of the gauge). so does this mean I can cross out the possibility of the coolant temperature sensor fail? my car has 4sp tippy and 160k on the clock.

If I decide to get a new o2 sensor to put on, should I get the mitsu genuine one or aftermarket would have better performance?

thanks for your advices
cheers
Kelvin

There are 2 temp sensors for Coolant.

1 for the Dash cluster guage - which you have noted does not move much

1 for the ECU - this is the one that the car uses to know how hot the engine is, and if it needs to add more fuel still to continue to warm the engine (as stated before by Tuffy)

The Cluster temp guage, doesnt actually interact with the car / ECU AFAIK

You can get O2 sensors off ebay for a Magna, dont know what ones but it can be done easily. Some people have even been as lucky to have the wire colours the same from the ebay part to the cars wiring loom too!

i have a 5 sp tippy and instant readout gives 12.0 city and average, goes down to 10.5 on longer trips, i.e. from melb to philip island (200kms). i drive a mixture of agressive to granma depending on traffic conditions and urgency..

I did this trip the other week in my manual TL and it did (if memory serves) around 8.5, the traffic wasn't heavy at all. Needless to say i was very impressed.