with petrol so cheap I've been running my TW wagon (auto, 135k) on petrol. Last time I measured the petrol consumption, it was 11-12L/100km around town. Now, it's leapt up to 17.5!

Before anyone asks, yes I do it by filling the tank to the top, yes, the odometer is accurate (within 2.5%), yes, this is over 3 fills of the tank, yes, it's driven carefully, no, there's been no change in driving habits. This is all around town driving.

It seems to be running fine. It had all new iridium plugs about 30k ago. The throttle body was cleaned last service, about 4-5 months ago. The air filter is maybe a year old. It gets regular service.

If anyone has any suggestions re possible causes I'll be grateful. I'll get them to check the O2 sensor next time it's in.

So you've been running it on gas or something?

yeah it's dual fuel, I usually run it on gas

Try disconnecting your battery for a while. Then plug it back in, drive it a couple of weeks and let us know. This will reset your long term fuel trims.

Or your o2 sensor is completely gone.

Why not continue to drive it on gas? Gas is still cheaper even though petrol is ~$1/l

Find a safe spot and look at instantaneous figures for steady speed 60, 80, 100.

Then tell us what numbers you get, a great indication of how well the O2 sensor is working.

driving pattern hasn't changed; consumption has soared; I'm thinking o2 sensor. How hard are they to change?

How hard are they to change?

Not hard. Mal will sell you one. It's been done and documented before, so do a search.

Dont forget that engine temperature/thermostat/temperature sender are also part of the equation. Engine must rise to the correct operating temperature within about 5 to 10 minutes from cold start.

Just a thought.
Petrol goes off and then additives settle out of solution to form a gritty substance inside the fuel tank (asphaltine).
How often has the petrol in the fuel tank been turned over whilst you were using mostly gas?
Had to throw away my fuel tank!

Gotta love those that don't read the first post. He's been doing it for 3 tanks, same driving patterns/routes as when he was on gas. Stop crapping up the thread with rubbish.

I read the post!

Maybe You use your noodle first before making a comment like that.
Asphaltine is insoluble and may have formed in the fuel tank, on the intank filter, inside the fuel pump etc etc.
All of these fuel component can impact on fuel consumption.

Hence I was asking what his fuel tank / petrol management has been whilst on gas.
Don't care about the recent 3 tanks use of petrol.

But hey I just presented this as a thought.

The crap is comment 10 above (it technically contributed nada, zip, zero!!!!).

PS:
> Since @ Neo continues to bait for a reaction - I'll just say: Not interested in perpetuating a tangent discussion.
> @ Neo seems to have a big crystal ball that shows that the OP knows the need to refresh petrol (great - my thought is now Null and Void!).
We are now waiting for the Crystal Ball to pinpoint the exact culprit besides the "its in response No 4" (please - which item in No 4!).

Are you filling at the same petrol station?

If so it maybe their petrol burns faster maybe share your money around and try a few different stations and see how the results go?

Common symptom of a stuffed O2 sensor.
How many kms has it done?
O2 sensors can start to go dodgy as early as 100,000 km, and often conk out completely by 200,000 km.
A new one for a Magna (it takes just one unlike a 380 which has four) is not all that expensive and it's fairly easy to DIY replace.
So if your kms are up there, even if a stuffed O2 sensor is not the cause of your problem, it probably should be replaced anyway as preventative maintenance.

Find a safe spot and look at instantaneous figures for steady speed 60, 80, 100.

Then tell us what numbers you get, a great indication of how well the O2 sensor is working.

The 3.5 and 3.8L engines are big lumps, and burn a lot of fuel just warming up to operating temperature.
Hence me wondering how many cold starts you do on a tank, that has more bearing on fuel consumption than driving style.

O2 sensors aren't consumable items, ie they don't wear out, but they can fail.
But replace it anyway, see what happens.

I read the post!

Maybe You use your noodle first before making a comment like that.
Asphaltine is insoluble and may have formed in the fuel tank, on the intank filter, inside the fuel pump etc etc.
All of these fuel component can impact on fuel consumption.

Hence I was asking what his fuel tank / petrol management has been whilst on gas.
Don't care about the recent 3 tanks use of petrol.

But hey I just presented this as a thought.

The crap is comment 10 above (it technically contributed nada, zip, zero!!!!).

Haha, stop over thinking things. The guy doesn't sound like an idiot, he knows more about this than you by the sounds. The solution is in comment #4 and not in any of the hot air you've been pushing out, sorry :P

Anyone on gas knows to run it or warm the car up on petrol then switch over. Leaving any and all of your comments null and void. But yea continue to harp on about it if you like.

I've tried running it on LPG for a few days: consumption is 30L/100km. So it's now cheaper to run on petrol than gas, but bloody expensive on both. Does the Impco factory gas use the O2 sensor?

I've tried running it on LPG for a few days: consumption is 30L/100km. So it's now cheaper to run on petrol than gas, but bloody expensive on both. Does the Impco factory gas use the O2 sensor?
All gas systems rely on the oxygen sensor - some directly (e.g. most mixer systems, which are wired to "intercept" the sensor signal) and the others by relying on the ECU using it (particularly vapour and liquid injection systems).

A simple test of the oxygen sensor, for petrol use only with a mixer system like yours, is to disconnect it (passenger side of centre console), reset the ECU (disconnect the battery for 10-15 seconds) and then drive test carefully monitoring fuel use. If fuel economy improves noticeably with the sensor disconnected, further investigation of the sensor is warranted; otherwise reconnect it. Resetting the ECU is critical to this test - the learned fuel trims will obscure the results otherwise.

new O2 sensor and gas and petrol consumption is now back where it was. All good now. Runs a bit better too.

So, what brand of sensor did you buy?

Part number?

And how much/where from?

I have done 162,000km now so it's probably time I started looking into changing mine.

Sorry, I don't know, I took it to my regular mechanic and he did it. I'll ask him. I think they probably went genuine, because it cost $172, which was a bit of a shock.

Geez, you could have got one for $43 and installed it yourself, see here: http://www.ebay.com/itm/OXYGEN-SENSOR-SUIT-MITSUBISHI-MAGNA-TR-TS-TE-TF-TH-TJ-TL-TW-VERADA-KS-PAJERO-NH-/221314583706

yeah, maybe.

yeah, maybe.

Not to worry. You will soon recoup your costs in fuel saved.

Question - was the old sensor covered in soot? I'm guessing it was, due to the very rich mixture. If so, it is an easy way to tell if an oxygen sensor has failed or not.

new O2 sensor and gas and petrol consumption is now back where it was. All good now. Runs a bit better too.

Good to hear.

Also, AQUAR is a noob.

Oh, don't forget to remove all the asphaltine from your tank and lines. lol


I'll move on now.

Also, AQUAR is a noob.

Oh, don't forget to remove all the asphaltine from your tank and lines. lol


I'll move on now.


@ Neo

How NICELY presented as a perfect example of being "narrow minded" and "unable to think outside the box".
All you did was repeat that which various expert AMC members have already mentioned many times in this forum.
All I did was present a thought in case the obvious causes fell through - yep I must be a NOOB and You are being Plain Immature.

Maybe if you weren't so self absorbed in beating your chest for pointing out "it must be the O2 sensor",
you might just search this forum for threads that show what happens to fuel tanks with stale fuel in them.

And now I'll move on.

At least the 'asphaltine' explanation is original, just about every problem on this forum these days is answered with 'must be coolant leaking on your ECU' and 'oxygen sensor is a dud, dude'.

Anyhow, everyone knows petrol goes off rapidly, 6 months without a fuel stabiliser in the tank is asking for trouble.
http://www.supercheapauto.com.au/online-store/products/STA-BIL-Fuel-Stabiliser-236mL.aspx?pid=223945#Recommendations

So, we now have one 'nOOb', one 'Plain Immature', and one 'annoying' person (me) in this thread. lol

. . . . I will move on too, now. lol

@ Neo

How NICELY presented as a perfect example of being "narrow minded" and "unable to think outside the box".
All you did was repeat that which various expert AMC members have already mentioned many times in this forum.
All I did was present a thought in case the obvious causes fell through - yep I must be a NOOB and You are being Plain Immature.

Maybe if you weren't so self absorbed in beating your chest for pointing out "it must be the O2 sensor",
you might just search this forum for threads that show what happens to fuel tanks with stale fuel in them.

And now I'll move on.

Yea nah, all I did was use my 8 years of experience working on exactly the same cars to tell him the exact issue based on the problem he was describing.

The reason why everyone else uses the exact same troubleshooting steps and or go straight to the most common things is because those are the most common problems so why wouldn't we tell him the most common cause based on what he's asking? If you want to be an idiot and get your tank descaled or whatever before replacing an obviously fault o2 sensor be my guest, but it doesn't make you any less of an idiot for doing so even if it's the most complex solution you can come up with. I mean come on, just go back and have a look for yourself.. you'll even find my crystal ball was right....


PS:
> Since @ Neo continues to bait for a reaction - I'll just say: Not interested in perpetuating a tangent discussion.
> @ Neo seems to have a big crystal ball that shows that the OP knows the need to refresh petrol (great - my thought is now Null and Void!).
We are now waiting for the Crystal Ball to pinpoint the exact culprit besides the "its in response No 4" (please - which item in No 4!).

Yeah it was in post number 4 all right. lol

Geez, you could have got one for $43 and installed it yourself, see here: http://www.ebay.com/itm/OXYGEN-SENSOR-SUIT-MITSUBISHI-MAGNA-TR-TS-TE-TF-TH-TJ-TL-TW-VERADA-KS-PAJERO-NH-/221314583706

Thanks for the link :)

Only reason I'd try a generic/unbranded eBay sensor is if I was getting rid of the car in the next 12 months.

Keeping it any longer than that, I'd stick with genuine.

@ Neo

Stop trying to imply to AMC members that I wanted the OP to go and "boil out" the fuel tank.
- A fuel tank contaminated in this way over a long period is scrap metal.
- The fuel lines are not affected the same way and don't need cleaning (understanding is not equal to experience!).
Stop trying to imply that I wanted the OP to NOT look at common causes that fit the problem.

All I did was present a THOUGHT that arose on account that the OP drives on GAS and recently switched back to GASOLINE.
In that thought the only thing I pointed out was that the fuel system might be compromised IF there had been inadequate turnover of the fuel in the tank.
Since when is that kind of input a reason for ridicule?
If you don't like some on topic input then either respond in kind or keep your thoughts private.

SO - stop trying to embellish the content of my input or quote it out of context - You are just highlighting your own reading problems!

At the end of the day - the OP ignored all AMC input and took it to the local mechanic.
That shows You where the trust lies.

Hopefully the admin team will now lock this thread before we gain more accoladed AMC members of the genre "NOOB" " Immature" and "self proclaimed Annoyance".

@ Neo

Stop trying to imply to AMC members that I wanted the OP to go and "boil out" the fuel tank. A fuel tank contaminated in this way is scrap metal.
Stop trying to imply that I wanted the OP to NOT look at common causes that fit the problem.

All I did was present a THOUGHT that arose on account that the OP drives on GAS and recently switched back to GASOLINE.
In that thought the only thing I pointed out was that the fuel system might be compromised IF there had been inadequate turnover of the fuel in the tank.
Since when is that kind of input a reason for ridicule?

SO - stop trying to embellish the content of my input - its just highlighting your own reading problems!

At the end of the day - the OP ignored all AMC input and took it to the local mechanic.
That shows You where the trust lies.

Hopefully the admin team will now lock this thread before we gain more accoladed AMC members than "a NOOB an Immature and a self proclaimed Annoyance".

Nah I'm just happy that it was what I said it was, and you said all posts from 10 and up were useless input. That's been my main concern really.

@ Neo,

I never said that all posts from 10 and up were useless.
Just another example that You just can't comprehend (or embellish!) what you read.

Pushing useless banter because you erroneously thought I discarded your input - how immature!.

Glad you are happy!
I'll leave you with the euphoria.

I know it could have been fitted with a cheaper unit, but I can see why my mechanic prefers genuine. The fuel economy has shown a big improvement, and it runs much better. I'm happy to assume that the old sensor was no good. At the moment I'm very busy and just don't have time to jack it up and fit a new one myself. I'm v happy with the fix.
Thanks everyone for the great advice.

I know it could have been fitted with a cheaper unit, but I can see why my mechanic prefers genuine. The fuel economy has shown a big improvement, and it runs much better. I'm happy to assume that the old sensor was no good. At the moment I'm very busy and just don't have time to jack it up and fit a new one myself. I'm v happy with the fix.
Thanks everyone for the great advice.

No worries, glad it's all good.

No worries, glad it's all good.

Yep, you have the peace of mind knowing you have a genuine Mitsu part fitted, it now runs like it should, so it's worth it for a few more $.

'Genuine Mitsubishi' = NGK, yes?

I believe "NTK" is the oxygen sensor brand name that was the original OEM fitment to the late model Aussie Magna's.

But it is the same Japanese company as "NGK" the spark plug manufacturer.

I am hoping "Cooperplace" is going to confirm what brand of sensor that has produced the good result for him.

And hopefully the correct part number.

Only reason I'd try a generic/unbranded eBay sensor is if I was getting rid of the car in the next 12 months.

Keeping it any longer than that, I'd stick with genuine.

Yeah very true.

economy on gas is now good, but still heavy on petrol. On petrol it was 12-13L/100km when the car was new. LPG is now about 16L/100k, which I'm happy with, petrol is still at about 15. Before fixing the O2 sensor it was 25-30 on gas and 18-20 on petrol, so there is a big improvement but still not ideal on petrol. No change in driving habits: driven gently around town. Also surging and lumpy on idle on petrol, but only in drive, fine in neutral; perfect idle on gas. Any suggestions for cause? I know the throttle body has been cleaned a couple of times.