Hi,

Maybe someone can throw some light on why my 2000 TH Magna wagon has increased fuel consumption from 9.3 l/100km to 10.3 with exactly the same running conditions and over a few thousand ks. Apart from using more fuel it drives exactly the same. The figure comes from the trip computer, but I have also verified it at various tank fill ups. The vehicle has about 140,000km. The check engine light has never come on.
Suggestions have been:
O2 sensor out of calibration
partly blocked fuel filter
Blocked PCV

The PCV was quite clean and rattled when shaken. I cleaned it anyway.
I tried today to replace the fuel filter but can not get the retaining clips to release to get the flexible line off. Is there some trick? The book says to squeeze in the clips and pull off. If only.
Can the O2 sensor be tested in situ?

Thanks,
Phil

I would say the O2 sensor could be on the way out, but you're doing the right thing by checking the easy/cheap things first :)

Have you changed your fuel type/station?

Hi,

Maybe someone can throw some light on why my 2000 TH Magna wagon has increased fuel consumption from 9.3 l/100km to 10.3 with exactly the same running conditions and over a few thousand ks. Apart from using more fuel it drives exactly the same. The figure comes from the trip computer, but I have also verified it at various tank fill ups. The vehicle has about 140,000km. The check engine light has never come on.
Suggestions have been:
O2 sensor out of calibration
partly blocked fuel filter
Blocked PCV

The PCV was quite clean and rattled when shaken. I cleaned it anyway.
I tried today to replace the fuel filter but can not get the retaining clips to release to get the flexible line off. Is there some trick? The book says to squeeze in the clips and pull off. If only.
Can the O2 sensor be tested in situ?

Thanks,
Phil

mine did this so I started using a different petrol station and it returned to normal about 10l/100km

Check your spark plugs, are they clean? If not check if your valve cover gaskets are leaking and replace them.
Apparently if your valve cover gaskets are a bit old and not sealing properly then there is a bit more blow by recirculating through your engine via the PCV and intake manifold causing the combustion chamber to soot up.
You would notice this by seeing black deposits on you spark plugs and muffler (providing your car doesn't have an obvious oil burning issue).

I had the same problem and after replacing the valve cover gaskets the fuel consumption went down.

Oh and this may seem obvious but check your air filter.

Oh and this may seem obvious but check your air filter.

+1.. mine went up about a liter per 100km... air filter was pretty filth..

Steve

ayne']mine did this so I started using a different petrol station and it returned to normal about 10l/100km

I reckon shhhayne is on to something. My economy was progressively getting worse. I switched from Safeway to BP, economy improved ~ 1 l/100km nearly straight away. So now I'm getting ~12.3 l/100km (AWD).

Ken

I reckon shhhayne is on to something. My economy was progressively getting worse. I switched from Safeway to BP, economy improved ~ 1 l/100km nearly straight away. So now I'm getting ~12.3 l/100km (AWD).

Ken

Is it the BP Ultimate that is the one their claiming ull get 40km's more out of tank than normal unleaded? and can you chuck that straight into your tank? Sorry if ive hijacked. just seemed an appropriate time to ask.

I just use the standard 91 RON unleaded. I haven't tried their "premium" fuels.

A few years ago when I tried the Shell Optimax (?) it made no difference. As far as I recall, the TL can't tune for increased octance rating, it has no knock sensor.

Don't let that stop you giving it a try though, it's not all about octane rating.

Ken

I was using an independent fuel station called freedom
and my fuel economy went down hill so i started using BP and now my fuel economy is better

a few locals have told me that the independent station 'waters down' there petrol with something

so idk
but yeh

Thanks for the replies everyone.

I did a 1200km round trip to Brisbane and still the same, so I don't think it is fuel supplier related. On a long run like that I used to get better than 9l/100km and it was nearly 10l/100km. I generally use Caltex in Armidale, NSW, but also use BP at times.91RON unleaded. Tried the higher octane some time ago ( when it was running OK) and got worse economy.
A friend says that his Magna gives very significantly better economy with E10 but I can not verify that.

I will try various ideas and after a few weeks post my conclusions.

Thanks,
Phil

I just use the standard 91 RON unleaded. I haven't tried their "premium" fuels.

A few years ago when I tried the Shell Optimax (?) it made no difference. As far as I recall, the TL can't tune for increased octance rating, it has no knock sensor.

Don't let that stop you giving it a try though, it's not all about octane rating.

Ken

exactly it snot all about the octane rating. Its about using the quality of the fuel the manual suggests. I sare say most 3rd gens were designed to run premium unleaded. SO basically give the car what it wants/ what it needs and by that i mean if the manual says premium unleaded thats either E10 98 octane or just straight PULP 95 ocatne (no added ethanol)

The misconception people have is that a knock sensor will magically add kms when you use a better fuel. Wrong. The claim made by BP also says "after continued use" not just fill up and get 40kms extra. A knock sensor is there to save an engine not part of the open loop processing done by the ecu, but will send info to the ecu to retard timing if the engine suffers a detoantion event.

The knock sensor tries to save an engine (say if you fuel pump fails/ an injector clogs/ anything that can cause detonation) the 02 sensor feedback is what tells the ecu if it needs to go richer or leaner, but once past a certain loadxrpm point the ecu switches to closed loop operation where it only takes in MAF/throttle/rpm readings to decide on how much fue lto inject. Nothing you do except a tune can change this fuel economy.

A knock sensor does not add timing. The ecu adds timing (up to a set amount) if at anytime this extra timing causes a knock the knocksensor says so and makes the ecu remove it. The better fuel creates less polution (to use not make) so its better for the environment but not your back pocket.

For a point in case my other car (not mitsubishi) would get 320-345kms on e10 premium 95 from 50 litres and would get 390-420 on PULP 95 (non e10) and 430-450 from PULP 98 octane non-e10 fuel why? because it was tuned from the factory to run minimum 95octane PULP (non e10) so when i used less quality fuel the knock sensor would not allow the ecu to add the extra timing (during cruise conditions and WOT) to get that extra economy i was getting because higher knock readings were present. The high octane PULP (98) also got me more since due to my engine setup the engine was able to use extra timing on higher engine loads then standard on 95octane due to the slower burning of the higher octane fuel.

I used to run the 98 all day every day but went back to 95PULP when the price difference got to 10c per litre up north.

cant believe no1 has said this, have you checked your tyre pressures?

i know you said that it happened suddenly, but it may have been building up to the point where pressures where too low and cause it to chew more juice.

I have always run 31 psi front, 29 psi rear. I put on new tyres after the sudden increase but no effect. Didn't expect any.
Phil

thats a pretty low tyre pressure

i would be running minimum of 34 (since 99percent of tyres are designed for that pressure) but optimumly would run 38-40.

each to their own i guess. this wont have much of an affect on fuel consumption, though 29 is getting low. at 29 my tyres start to bulge out definetly like they are under inflated.

even 34psi is low, i run 38-40 all round

To those saying 29 is low......

Have you even bothered to look at the little tyre placard?

Then again, lots of people must know better than tyre manufacturers and a car manufacturer :)

Running at 32/29 my last set of tyres lasted nearly 70,000km and wore very evenly. They were rotated and balanced about 4 times. Magna TH wagon.

Another reason for running more moderate presures relates to damage from gravel roads. (which we have here) High pressure and gravel roads lead to increased tyre damage, yes including sidewall damage. Ask outback operators and tyre fitters. They see so many problems arising from excessive pressures. The idea that a sidewall bulge means that the pressure is quite wrong. It may be a hangover from the days of bias ply tyres. When the tyre goes over a bump the sidewall will bulge anyway and if too much pressure that is when damage occurs.

Phil

To those saying 29 is low......

Have you even bothered to look at the little tyre placard?

Then again, lots of people must know better than tyre manufacturers and a car manufacturer :)

the psi stated on the tyre placard on the car is always too low, any tyre salesman will tell you this. they put the psi that low on new cars to give a softer ride.

the psi stated on the tyre placard on the car is always too low, any tyre salesman will tell you this. they put the psi that low on new cars to give a softer ride.

and the winner is....

tyre manufactuerers set the tyre pressure for the pressue which gives the best compromise between mileage and comfort. Negating comfort, you get a lot more mileage from them

on my last 2 cars ive had over 70,000 and 65,000 kms from a set of 215/60/15's. Had them rotated and balanced as neccessary, and also pumped them back up to 42f and 40r everytime i left the tyre centre as they would always lower them to 34. the set that lasted 65'000 was on a turbo coupe that doubled as my girlfriend, so it copped a hammering at times.

I cannot comment on the effect of gravel roads, hasnt ever been a concern for me, due to where i live. As the car gets older, it will use more fuel, as things like compression slowly lowers, and scum slowly builds up in the engine. As the gearbox wears it takes more to turn over. All the sensors would be showing their age ealding to slow sign changes and or singal drop out at times. Try changing your thermostat. If its opeining to early it will mean the car spends longer in 'cold start' using just that little extra fuel. there is heaps to do and check. have fun

Lionel

the psi stated on the tyre placard on the car is always too low, any tyre salesman will tell you this. they put the psi that low on new cars to give a softer ride.

Then pump your tyres up to 60PSI.....whatever, i'll take an engineers word over a salesman.

Then pump your tyres up to 60PSI.....whatever, i'll take an engineers word over a salesman.

im sure the fact mitsubishi signs your engineers checks has nothing at all to do with his findings

when it comes to tyre pressure refer to information that comes from the engineers that designed the tyre youre running, not the engineer that has no idea what tyre youre running. its pretty simple mate

I wonder how many members who suggest putting a higher air pressure then what Mitsubishi recommends on the car placard, are riding on standard rims and tyres?

I have standard rims with Khumo 205/65 tyres, and when I had a full set recently fitted, the tyre guy put 36 psi, and I jumped around on the road and had a hard ride. And that is on city roads.

When I contacted the tyre people about it, they said the higher pressure prevents the shoulders from wearing out. However, it was the same tyre people that I had bought the previous same tyres from and they recommended 32 psi at the time. So I split the difference and use 34 psi and I am very happy with that pressure.

Ozz

Some additional info

exactly it snot all about the octane rating. Its about using the quality of the fuel the manual suggests. I sare say most 3rd gens were designed to run premium unleaded. SO basically give the car what it wants/ what it needs and by that i mean if the manual says premium unleaded thats either E10 98 octane or just straight PULP 95 ocatne (no added ethanol)

For 3rd Gen the manual says
"Your vehicle must use unleaded petrol (ULP - 91 RON minimum) only"

The misconception people have is that a knock sensor will magically add kms when you use a better fuel. Wrong. The claim made by BP also says "after continued use" not just fill up and get 40kms extra. A knock sensor is there to save an engine not part of the open loop processing done by the ecu, but will send info to the ecu to retard timing if the engine suffers a detoantion event.

The knock sensor tries to save an engine (say if you fuel pump fails/ an injector clogs/ anything that can cause detonation) the 02 sensor feedback is what tells the ecu if it needs to go richer or leaner, but once past a certain loadxrpm point the ecu switches to closed loop operation where it only takes in MAF/throttle/rpm readings to decide on how much fue lto inject. Nothing you do except a tune can change this fuel economy.

A knock sensor does not add timing. The ecu adds timing (up to a set amount) if at anytime this extra timing causes a knock the knocksensor says so and makes the ecu remove it. The better fuel creates less polution (to use not make) so its better for the environment but not your back pocket.

For a point in case my other car (not mitsubishi) would get 320-345kms on e10 premium 95 from 50 litres and would get 390-420 on PULP 95 (non e10) and 430-450 from PULP 98 octane non-e10 fuel why? because it was tuned from the factory to run minimum 95octane PULP (non e10) so when i used less quality fuel the knock sensor would not allow the ecu to add the extra timing (during cruise conditions and WOT) to get that extra economy i was getting because higher knock readings were present. The high octane PULP (98) also got me more since due to my engine setup the engine was able to use extra timing on higher engine loads then standard on 95octane due to the slower burning of the higher octane fuel.

BURN RATE V. OCTANE
Do High-octane fuels burn faster than low-octane fuels?

"There's a perception that higher octane fuels burn quicker and that's why they're more efficient, but this isn't true - burn rates for all fuels are the same.

However, with higher-octane fuel you can run what we call a leaner mix, which means more air to fuel. To move through that space with the air, it has to burn quicker, but the burn rate is still the same."

I used to run the 98 all day every day but went back to 95PULP when the price difference got to 10c per litre up north.


Ethanol-blended fuels-Update from the technical manager at BP
How might these fuels affect your vehicle's performance ?

"For a reasonably modern vehicle you should expect to experience the same or even better engine performance.

Because ethanol increases the octane of the fuel, you may experience the benefit of a higher octane. For example, if the engine has a knock sensor, it will recognise the higher octane and change its mode of operation to take advantage of it and run more efficiently

Vehicles that don't recognise octane levels will still get a benefit if they're under load
For example if you drive a heavier vehicle such as a four-wheel drive, you're going up a hill, or you're pulling a trailer or caravan, the higher octane of the ethanol blend means the fuel wil burn better and the engine will 'see' more power.

Is this improvement in engine performance something a driver would notice?

If their car has been well maintained, a driver will notice the improvement, particularly if the vehicle is under load
Since a lot of cars have small engines in big bodies, they're under load nearly all the time"

Of course a TJ Magna for example has a LARGE engine in a large but relatively light body

Cheers, Barry