Since I had the car (bought her when she was 9 months old) this is the only problem I have had with her...

She has been chewing a fair bit of fuel, round the 300-330kms mark and with the air con runnnig often during the "summer" (the one we briefly expirienced) about 300kms. I tried driving extra light on the pedal, using no air con, using only air con full ball etc and nothing really seemed to make much differnce. As I said I was chewing 300kms a tank and the trip computer was readying in the 15L/100kms bracket.

I have been to the mechanic when I had the car serviced and he had a look over it and couldn't find anything wrong and even after the service a lil while ago nothing changed.

Then all off a sudden after I filled up once again my fuel economy has returned, dropped down into the 13'sL/100kms bracket and getting more Ks out of a tank :)

Any ideas on what could of caused it?

If it was a blockeage i would of used less fuel, correct?
Weather has cooled off but it should make anywhere near that much difference if any.

Car Specs
02 Seris II TJ Exec
3.5L Auto
POD Filter in box and CAI
Pacie Extractors
Stock CAT and resi, dual exhaust at the rear

All mods have been done for awhile before this issue arose so its not likely it is due to one of them and the car as has always been run on premium or ultimate.

I'm afraid your maths don't quite add up. If you're getting 15/Klms around town with the air con on that's about normal for a 3.5 auto in traffic - but that also equates to about an easy 450 klms per tank, not 300-330klms. (sedan tanks are 71 Litres, wagons are 68 Litres, AWD sedans are 65 Litres)

Anyway remember that with wider tyres you have a much increased rolling resistance - per chance your sudden change in consumption coincides with you putting some air in the tyres?

Pod filter probably isnt that sensational, dunno if you have the proper cai set up that the other guys have had.

Try running the tyres with a slightly higher psi also.

Did you always buy your fuel from the same servo? Could be crap fuel, or faulty fuel sender/fuel filter unit.

Thats seems bad mate, have you had your injectors cleaned or decarbonised the fuel lines?

Also check the tyres.

Since I had the car (bought her when she was 9 months old) this is the only problem I have had with her...

She has been chewing a fair bit of fuel, round the 300-330kms mark and with the air con runnnig often during the "summer" (the one we briefly expirienced) about 300kms. I tried driving extra light on the pedal, using no air con, using only air con full ball etc and nothing really seemed to make much differnce. As I said I was chewing 300kms a tank and the trip computer was readying in the 15L/100kms bracket.

I have been to the mechanic when I had the car serviced and he had a look over it and couldn't find anything wrong and even after the service a lil while ago nothing changed.

Then all off a sudden after I filled up once again my fuel economy has returned, dropped down into the 13'sL/100kms bracket and getting more Ks out of a tank :)

Any ideas on what could of caused it?

If it was a blockeage i would of used less fuel, correct?
Weather has cooled off but it should make anywhere near that much difference if any.

Car Specs
02 Seris II TJ Exec
3.5L Auto
POD Filter in box and CAI
Pacie Extractors
Stock CAT and resi, dual exhaust at the rear

All mods have been done for awhile before this issue arose so its not likely it is due to one of them and the car as has always been run on premium or ultimate.

Ways to improve your FC.

1) Check your tire pressure, made sure it's up to mark. --- low tire pressure
2) Use a plastic safe electro contact cleaner and clean the AFM sensor --- dirty sensor, inaccurate reading
3) Use a bottle of SI-1 (Shock dose, 1 bottle per tank) --- injector & valve clean
4) Reflash your ECU by disconnecting your car batt for at least 15min --- reboot ECU to factory map
5) Change your eng oil to any synthetic 30wt oil be it 10w30 or 5w30. --- lower component drag, improve engine efficiency
6) Drain and top up your ATF fluid. Change the filter too. --- could be torque slip
7) Check your plugs, if it's foul, change to a hotter plugs. --- normal tune up

I'm afraid your maths don't quite add up. If you're getting 15/Klms around town with the air con on that's about normal for a 3.5 auto in traffic - but that also equates to about an easy 450 klms per tank, not 300-330klms. (sedan tanks are 71 Litres, wagons are 68 Litres, AWD sedans are 65 Litres)

Anyway remember that with wider tyres you have a much increased rolling resistance - per chance your sudden change in consumption coincides with you putting some air in the tyres?

I wouldn't say around town, i don't do a hell of alot stop start driving. I live 10 minutes down the road from work and have 7 turns to get to work and non-stop driving inbetween.

And I never said it was my maths, just saying what the trip computer said...

A few things to think about but as i said it has come good again. I wasn't really that worried about it when I thought it was chewing fuel, figured i would find out what it was and fix it. When it magically fixed itself has made me start to wonder...

As far as the same servo, there are a couple of use on a regular basis but all 3 of them are different companies.

Will check my tyres and get some injector cleaner tomorrow anyways, i used some ages ago but not for a while...

Thanks guys.

"I wouldn't say around town, i don't do a hell of alot stop start driving. I live 10 minutes down the road from work and have 7 turns to get to work and non-stop driving inbetween.

And I never said it was my maths, just saying what the trip computer said..."

which 'commute' isn't that dissimilar to mine and I stand by what I said above - in such circumstance your 'choke' is running 1/4-1/3 of the trip etc etc - and 15L per 100 is about what to expect - especially with the aircon on.

re the maths / what the computer said - are you doing the 'Zeroing' where you hold the mode button for 3 beeps after you first start after filling up - if not do so because whether out of the computer or not your figures don't add up.

My 3.5l manual now averages a 11-12l p/100klms and I mostly do 100-110km/h continuos trips(live in the country). I thought this was pretty bad too.
Had it serviced and mitsu used some "special spray" in the throttle body to disolve the gunk which apparently can build up.
This made a bit of difference as I was on average of 13l p/100 klms.

Luke

which 'commute' isn't that dissimilar to mine and I stand by what I said above - in such circumstance your 'choke' is running 1/4-1/3 of the trip etc etc - and 15L per 100 is about what to expect - especially with the aircon on.

re the maths / what the computer said - are you doing the 'Zeroing' where you hold the mode button for 3 beeps after you first start after filling up - if not do so because whether out of the computer or not your figures don't add up.

But as i said, i have tried with the air con off and on and didn't make much of a difference and yes I do zero my trip puter each time i fill up.

I have driven my car for over 2 years so i knew the fuel economy etc of the car pretty well, i knew what to expect and then for a few months or so this problem arose and then disappeared.

My 3.5l manual now averages a 11-12l p/100klms and I mostly do 100-110km/h continuos trips(live in the country). I thought this was pretty bad too.
Had it serviced and mitsu used some "special spray" in the throttle body to disolve the gunk which apparently can build up.
This made a bit of difference as I was on average of 13l p/100 klms.

Luke


Thats still quite a lot even if the aircon is on. I normally get very good FC in country roads, despite my 2.4L engine for a 3rd gen magna, was getting 8-9L p/100km easily and sometimes even better. Since you have cleaned it maintain it with petrol cleaners.

Quite often when i go from putting regular unleaded fuel (argh) in my car to 98 octane, my trip computer will actually increase to about 12 - 13.5L/100Ks from like 10 -11L. My overall K's do increase with the better fuel, but its weird how the computer does this, maybe because the ECU is confused by the higher octane, i don't know.

I don't think that the trip computer can be all that accurate all the time.

I'd check your tures and your oxy sensor and forget about resetting your computer.

A crook oxygen sensor could result in up to a 10 percent decrease in fuel economy, so if your car is using 14L/100km a remedied oxygen sensor will result in 12.6L/100km in theory. There are methods to test it in theory, I believe the oxy sensor in the newer Magna's are preheated? so only one of the wires is a sensor wire. An electronic voltmeter with a lead on the sensor wire and one on the car body should show a voltage that changes quickly between negative and positive, it should be very quick as the sensor is quick. Be aware that it will be hot as they don't work till 600C or something. Theres information about testing it on the web I suggest you look there if you want to see if thats the problem. Generally they don't fail readily, but contaminates can be a death warrant to them apparently. Silicon used for gaskets etc can stuff them up, replacing it will help you out until more silicon residue gets in the exhaust... They're not overly expensive though, and can be installed yourself if your game! Any body on here actually tested one out on the new Magna's? I've got a TP which is a lot simpler since the sensor is in plain view at the front of the engine and the wire runs up right next to the radiator where its plugged in. Like with mine a faulty plug didn't help...

Anyways I hope you get everything sorted out with it! Are you sure you haven't accidentally caused a misconnection in any other sensor wire like from the air intake (I can't remember where the sensors are on the newer Magnas). I've seen that before and the only way the person knew was because they were getting 11L/100km on the highway in the 3.5 instead of their usual 8.5L/100km. They had a look and the wire broke off, now they're back to 8.5L/100km since the wire has been fixed... just a suggestion :)