Gday all,
I seem to have a problem with my fuel econony and putting it out there so see if anyone else has had similar probs and what the test/fix is?

I drive a 2007 380 SX
I refuel with 91 unleaded (never use 95, 98 or E10).
My range guide display went from showing 730km (every full tank before) down to 450km (evey tank full since)
The speedo matches 450kmish when I drive (i beleive the range display is reading right) which means somewhere I am using alot more fuel.
I took it into the Mitsu dealer and they asked me to record fuel usegae and bring it back, and i looked in the workshop manual but it doesn't really talk about the issue or it says plug the computer in and it will tell the fault.
Which means its upto me to fix it.

Let me know what you think or if you meed more info to give me a hand.

The range to empty is calculated based on your average fuel consumption from the last tank or so.

If your driving was predominantly country, and then you did a tankful of city stop and start, the predicted range could easily change by that much.

My predicted range is always around 450km because I always drive around the city. If I do a big multi-day country trip, it settles down at around 700km when I refuel.

The fuel quantity senders in the 380 are reliable. I doubt it is a sensor issue.

And if you have been driving around on 91, you should look at adding an upper cylinder lubricant or fuel injector cleaner to better maintain your fuel system.

I thought this could be the issue of change in driving patterns but, I haven't changed in patterns. Plus the range drop was instantaneous. Since i bought the car, it has alwasy read 730km on a full tank until recently. My first step was to reset the digital display but (appart from resetting most figure) its stayed with a range max of 450km

As flyboy said, run an injector cleaner through the car. I would suggest going through a tank of 98, less hassle.

What is your driving pattern like? Have you noticed any changes in the responses/behaviour of the car?

How many k's has the car done matey?

My predicted range is around 450 km; I only do city driving.

When the range guide was showing 730km were you actually getting that range?

And you are saying that you must be "using more fuel" - on what basis do you say that - what was your actual consumption for a similar trip before and after (putting aside what the guide says).

What does the 'instant' fuel usage show as? Have you got any fumes coming into the car or can you see if there are any signs of fuel dripping onto your garage/carport floor? You might have a loose fuel line or a cracked pipe.

In a manual, at 60km/hr in fifth gear, you should get around 6.0L per hundred instantaneous on a dead flat road.

Maybe if someone could post the auto instantaneous value at 60 you could compare.

Upper cylinder lubricant has done wonders for my 380. It's had 98 octane its whole life, so I thought it wouldn't benefit. It certainly did.

Resetting the trip computer will not actually reset what it will say. What it says it based on long term fuel trims that are stored in the ECU.

I've never had to reset and test the fuel trims before, I've always just had a look at them using EVOSCAN > 3rd gen ECU. Never actually had to look at them on a 380 or reset them, so it could be different.

Have you ever had the engine light flash up on you? Could be an issue with a sensor not reading what it should (faulty). Has your fuel economy actually gone up l/100km? Or is it just the expected range gone down?

Maybe see if anyone can confirm that unhooking the battery will reset it for sure before going and doing it.

Fuel trims should be below 5% on evoscan. Any higher and its running rich and could be from a range of reasons. The other thing is try resetting the trip everytime you fill up. Hold the mode button.

Id be checking the o2 sensor myself. It wont throw a engine light. Its a 30min job to replace.

Id be checking the o2 sensor myself. It wont throw a engine light. Its a 30min job to replace.
380 has four (4) oxygen sensors and the ECU will show a CEL light if it thinks there's a sensor related problem (unlike a Magna).

Hi all
Thanks for you replies,
On the last tank of 91 fuel I drove 480km burning 60lts with an avg of 12.6lt/100km at avg speed of 40km/h
Ive now got a tank of 95 fuel to compare with and its not comin up with much better results.
I did some research on the cars specs and I should be getting close to 10.8lt/100km with a range of 620 on 91 fuel. The car has done shy of 180k and I am getting ready to do the applicable service on it.
My driving isnt ultra stop go urban as I don't live in a city, (more like a built up town) It does about 40-60km a week day in speed zones of 60-100km/hr. There is about 4 trafic lights on the route it does.
I have thought it may be the o2 sensors (or one of them), but I can't find out how to test them to find out which one it is (if any). Is there a way for a multimeter or clampmeter type tool to test them? And what should it read.
But then WytWun said it should have a caution come up.
Other than this the car runs and sounds fine.
Once again thanks for everyones inputs.

It is possible that either or both of the primary oxygen sensors (the ones closest to the cylinder heads) is going bad without the ECU being able to determine this yet. The 380 I believe supports fairly standard OBD2 logging (unlike the Magna/Verada) which might be able to report on the fuel trims if you can get access to suitable tools. Very positive fuel trims (>+10%) would suggest checking the oxygen sensors more closely (such as pulling them out to check for carbon buildup).

Hi all
Thanks for you replies,
On the last tank of 91 fuel I drove 480km burning 60lts with an avg of 12.6lt/100km at avg speed of 40km/h
Ive now got a tank of 95 fuel to compare with and its not comin up with much better results.
I did some research on the cars specs and I should be getting close to 10.8lt/100km with a range of 620 on 91 fuel.

12.6lt/100km at average of 40km/h sounds like perfectly normal fuel consumption for this car.

My average speed is lower than that (about 35km/h) and I get about 14lt/100kms so what you are getting sounds right.