O2 Sensor

[calebR33]

So reading about O2 sensors it seems that it is almost always the issue with fuel consumption!

I am also experiencing bad consumption on my (RB25DE neo) getting probably 300 km per tank (not accurate but somewhere around that)

But i also read that an old/not working O2 sensor makes the car run rich. I dont think my car is running rich because theres NO smell at all of fuel, no misfires, no bangs (stock exhaust though)

So i was wondering... does that mean my O2 sensor is fine and i should check other things ??

Thanks for reading this long post

[Moodles2]

Change it anyway, if that doesn't solve it then check into other things

[calebR33]

Also i dont tink the car has been serviced for a while (need to do it asap!) does that affect fuel economy NOTICEABLY ?

[Moodles2]

List of things I can think of that could affect economy, driver, dead o2 sensor, worn out spark plugs (especially if copper ones), leaking fuel injector (internally or externally), leak in the fuel system (lines etc), borderline flat tyres, faulty coolant temp sensor (ECU stuck in open loop mode), dirty AFM.. and possibly using a completely stupidly thick oil like 20w60.

[calebR33]

Well its definately not the driver since i was trying to keep it under 2k rpm expect for the occasional times where i gave it a bit

But from the previous owner , he says it hasnt been serviced since SEPTEMBER!. almost a year... so hopefully ill get it servided soon! thanks for ur replies!

[mad082]

ok, there are a few things to consider when talking fuel economy. firstly is that you shouldn't just say "i get XXXkms to a tank". you should take note of how many litres you are putting int so you can work out your exact fuel economy, because everyones fuel gauge reads differently, and the point that you fill up varies as well, so you could be getting ok fuel economy and not realise it.

secondly is that the rpm you change gears at is only half the story. your amount of throttle percentage plays a big factor as well. if only rev to 2000rpm but use 50 to 75% throttle then you will use more throttle than someone who revs to 3000rpm but only uses 30 to 40% throttle.

as for the o2 sensor, they only work at light load, so if you drive like above (low revs but high throttle %) then your fuel economy won't be affected much by a failing o2 sensor. also the difference the o2 sensor makes at lower rpm isn't super huge, hence why you won't smell the car running rich. it's not like it is dumping in heaps of extra fuel. the actual difference in fuel economy is only around 20 to 25%. with the o2 sensor working the AFR will be around 14.5:1. when the o2 sensor is disconnected it will run around 11.5:1. the o2 sensor can be checked with a multimeter.

driving style generally plays the main part in fuel economy. doing short trips, or start/stop driving, or just plain spirited driving will dramatically increase fuel economy. a lot of the time, what young guys think of as driving like a granny is still medium acceleration and they could actually drive more economically.

as someone said before, if there is actually a fault causing poor economy it isn't just limited to the o2 sensor. thermostat can play a big part. if the car doesn't come up to temp within the first 5 to 8 mins of driving, and doesn't sit in the middle of the temp gauge when up to temp, then your thermostat isn't working properly and causing the ecu to run in cold start enrichment. dodgy wheel bearings or sticking brakes can also play a part. just jack the car up and try turning the wheels (obviously with the handbrake off and in neutral when checking the rears). plus all the ones listed above.

as for not being serviced since september, that isn't that bad, depending on how many kms it's done. if it has done lots of kms in that time then yes it's bad, but if it wasn't a daily then it isn't so bad, but even then it should be changed at 6 monthly intervals because oil degrades over time.

[calebR33]

Thanks for the essay i see you reply to every economy thread! haha

Well firstly i havent had the car long enough and havent fueld and measured accurately but the previuos owner did say 250km. But at the rate its going now im thinking itll go over 300km on the tank. (very rough)

As for the granny driving i was going really slow! It would take ages to reach 60 . And also the thermostat or whatever has no issues car warms up in like 2 minutes

But i gotta admit. The only trips we do are short. Generally 10-20 min drives. So if that plays a big role, then maybe its that!.

but ill definitely check into the wheels, and do a more accurate measure of my economy when i can!