Excessive fuel consumption in 2.5L Outback (MY02)

Lalbert · Post by **Lalbert** » Tue Dec 13, 2011 4:23 pm

Many months ago, I noticed a step up in fuel consumption, from about 10.5L/100km (typical) to about 12L/100km. Since then, it has been getting progressively worse. The car is now using over 13L/100km. It got new plugs and a new O2 sensor fitted recently, but problem remains. Any other suggestions on what could be faulty? There has been no change in driving habits, location, fuel type used, etc. Also no noticeable degradation in performance or other unusual symptoms, e.g. exhaust smoke, although it often smells of H2S ... but I think that's normal for the crap unleaded fuels we use here (high sulphur content).

niterida · Post by **niterida** » Tue Dec 13, 2011 4:46 pm

Blocked / collapsed cat ?

thunder039 · Post by **thunder039** » Tue Dec 13, 2011 5:53 pm

heavily dirty air filter

sven '2' · Post by **sven '2'** » Tue Dec 13, 2011 10:20 pm

niterida wrote:Blocked / collapsed cat ?

+1

10 years is about the effective life of a cat - esp if city bound

INEEDABEER · Post by **INEEDABEER** » Tue Dec 13, 2011 10:29 pm

I would say a faulty oxygen sensor.Mine did the same and I found a genuine one on ebay.

NachaLuva · Post by **NachaLuva** » Wed Dec 14, 2011 12:09 am

Lalbert wrote:Many months ago, I noticed a step up in fuel consumption, from about 10.5L/100km (typical) to about 12L/100km. Since then, it has been getting progressively worse. The car is now using over 13L/100km. It got new plugs and a new O2 sensor fitted recently, but problem remains. Any other suggestions on what could be faulty? There has been no change in driving habits, location, fuel type used, etc. Also no noticeable degradation in performance or other unusual symptoms, e.g. exhaust smoke, although it often smells of H2S ... but I think that's normal for the crap unleaded fuels we use here (high sulphur content).

The H2S smell like bad eggs isnt from a high sulphur content in petrol, its from the cat burning unburnt fuel from the engine running rich...which of course explains your poor fuel economy. Thing is whats causing it to run rich?

I'm guessing if you've gone to the trouble of replacing the O2 sensor you've replaced the air filter. You've done plugs, how bout the leads? Although a bad lead shouldnt have that big an effect & you would notice it in performance. When you pulled the plugs what did they look like?

Other things that affect economy are things like dirty injectors. Cant think of anything else...

Let us know if you find out what's causing your problem.

alang · Post by **alang** » Wed Dec 14, 2011 5:40 pm

i had the inside of a cat collapse on me it wouldn't let me accelerate over 2500 rpm. it had just gone, so pulled it off found a star post fence and smashed the guts out of it. the car went great hadn't gone that good for a long time

Alan

Brumby Kid · Post by **Brumby Kid** » Wed Dec 14, 2011 6:22 pm

alang wrote:i had the inside of a cat collapse on me it wouldn't let me accelerate over 2500 rpm. it had just gone, so pulled it off found a star post fence and smashed the guts out of it. the car went great hadn't gone that good for a long time

Alan

Yeah, it would be more "free flowing"
Apart from illegal, it is also dangerous, the fumes are very toxic, and the cat is there to convert them to less harmfull ones, you defanatly don't want to breath them!

My 2c.

Cheers Cam

Gannon · Post by **Gannon** » Wed Dec 14, 2011 6:36 pm

Might be a silly question, but have you started carrying more in the boot? I took out my tool box last week and have noticed an instant improvement in power, handling and fuel economy.

NachaLuva · Post by **NachaLuva** » Wed Dec 14, 2011 6:53 pm

Gannon wrote:Might be a silly question, but have you started carrying more in the boot? I took out my tool box last week and have noticed an instant improvement in power, handling and fuel economy.

That must be a serious toolbox haha. You're right though, unnecessary items just add weight affect handling & economy.

Dad used to call us kids extra weight lol

Gannon · Post by **Gannon** » Wed Dec 14, 2011 9:16 pm

nachaluva wrote:That must be a serious toolbox haha

Its actually a plastic kerbside recycling crate with a set of ring spanners, a set of sockets and a small toolbox containing a bunch of random tools. It also often also holds random parts that im moving around.

Then there is my work tool bag, and then there are my 2 dewalt drill boxes. It all adds up. Especially if I throw a few drums of cable in the boot for weekend cash jobs.

taza · Post by **taza** » Wed Dec 14, 2011 9:27 pm

nachaluva wrote:That must be a serious toolbox haha. You're right though, unnecessary items just add weight affect handling & economy.

Dad used to call us kids extra weight lol

haha. For a while I wouldn't even want my mates to have a water bottle in the car if they rode in my Foz because thats extra weight. lol

ScubyRoo · Post by **ScubyRoo** » Thu Dec 15, 2011 7:53 am

Tire pressures?

Lalbert · Post by **Lalbert** » Thu Dec 15, 2011 2:46 pm

Thanks to everyone who replied to my post. Except for the cat converter and temp sensors, I've tried all your suggestions. I think if a temp sensor was faulty, it would affect performance as well as fuel efficiency, but I might try a swap anyway.

steptoe · Post by **steptoe** » Thu Dec 15, 2011 2:50 pm

need to find a mechanic that uses an onboard af meter and take it for a drive to see what your emissions are doing

alang · Post by **alang** » Thu Dec 15, 2011 3:15 pm

on some cars you can disconnect the computer and give it 5 minutes then re connect sends it back to factory default. after starting and driving from X amount of time it sets up your fuel economy and sensors or get a printout of your computer

Post by **Alex** » Thu Dec 15, 2011 4:12 pm

yep, take the negative battery lead off for afew hours. Just nudge the brake pedal while its disconnected to drain every single piece of power left in the system.

then once re-connected take it for a soft drive for a while, it will remap the ecu to more economical driving. If you drive it hard youll get more power and higher fuel consumption.

Post by **TOONGA** » Thu Dec 15, 2011 6:31 pm

To remap the ECU

To erase the codes or "Reset the ECU" is by doing the infamous "battery dance."
NOTE: Do this on a "cold" engine. Leave it sit overnight and do it in the morning.
1. Disconnect the negative battery terminal cable for 45-60 minutes.
2. Reconnect the negative battery terminal cable.
3. Turn off all your accessories.
4. Start the car, but DO NOT touch the throttle at all.
5. Let the car idle for 10-15 minutes, or until the car is at normal operating temperature. Again, do not touch the throttle.
6. Turn the ignition key to the "OFF" position.

This will let you remap the ECU to a different driving style.

from this thread showthread.php?t=14372

TOONGA

Gannon · Post by **Gannon** » Fri Dec 16, 2011 5:25 am

Sorry guys, but that is a huge misconception.

The ECU mapping is fixed and the only way to change it is to reflash the EPROM
When you remove power from the ECU, the details on ignition advance per knock detection and light load fuel trim are forgotten and after 15 or so minutes of driving it relearns them. But the ECU is forever changing these values, as ambient air temp changes, and as you go through different batches of fuel. And these saved values are continuously updated for the entire life of the car.

When you 'drive it like you stole it' , you are using the upper section of the load, fuel and ignition maps, which is completely different to the lower part of the maps that you would use when 'babying it'

YouTube · Post by **El_Freddo** » Fri Dec 16, 2011 8:59 pm

Gannon wrote:Sorry guys, but that is a huge misconception.

+1. I've always thought the same. I reckon people just use the "re-map" as an excuse to do some spirited driving that they wouldn't usually do...

Cheers

Bennie