fuel consumption enigma

Hello,

I have been searching to find info on this problem. The car is a Mitsubishi Space Star 1.3 16 V 1999.

Normal consumption averaged 6.2 l / 100 km. After a while, but suddenly, fuel consumption lowered, starting at 5 l to even 4 l / 100 km. And this on average and instantaneous rate.

A fill up at the gas station confirmed the figure from the onboard computer.

Does anyone know how this consumpton is calculated, and could this mean a sensor has gone faulty ?

The odometer has no significant fault, only 10 %, which would not explain the problem.

Any help warmly appreciated,

Regards,

Carl

Reply to
carl
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Causes of poor fuel consumption include (in no particular order):

1) Failed / failing lambda sensor (also known as oxygen sensor). See
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2) Incorrect tyre pressures

3) Failed thermostat - does the engine get up to operating temperature OK?

4) Failed temperature sensor - if it gets to the right temperature, does the engine managament system know it?

5) Binding brakes - do any of the wheels feel far hotter than they should? Does the car "Lurch" to a halt, or gently glide to a stop?

6) Fuel leak - should be obvious by the smell! (But I guess if the computer is showing poor economy this is not the case for you..)

and finally, and most obviously

7) Forgetting to remove roof-rack, trailer or caravan ;-)

Ian

Reply to
Ian Riches

"Ian Riches" wrote

In this case it's not poor fuel consumption, it's an exceptional good fuel consumption.

If a fill up at the gas station confirms the onboard computer, it's probably not faulty.

Don't touch the perfectly running system!

Thomas

Reply to
Thomas Schäfer

Ian Riches ( snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

Umm, Ian...

6.2l/100km is 45mpg 5l/100km is 55mpg 4l/100km is 70mpg.

So this is the economy that the trip computer's reporting? Personally, I think the computer's lying through it's teeth...

(I presume it isn't *really* doing 70mpg? If it is, find the problem, and bottle it. You'll make your fortune.)

Reply to
Adrian

Ooops. Teach me not to read properly and confuse my l/100km with mpg.

In that case, look for air leaks.....

Ian

Reply to
Ian Riches

I know. Blame confusion of l/100km and mpg, not being used to people complaining about *improved* fuel economy and publically embarassing lack of comprehension skills.

I suspect one of those may be more to blame than the others.

Oops.

Ian

Reply to
Ian Riches

Ian Riches ( snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

A definite rarity...

Reply to
Adrian

Pop your spark plugs out and have a look at them to see if there are signs of it running lean.

Reply to
Depresion

The fuel consumption is normally calculated with the injection time on this injector by the ECU. The fuel consumption is given as frequence signal to the computer. This is most of the system anyway.

A really good fuel consumption can mean a lot of thing, from the ecu calculating wrong to a computer problem. As your engine is still running fine, I do not thing that the ECU is gone.

I will personnaly tip on a signal problem betwwen the ECU and the computer. This could be chekced by any good repair shop.

Another possible problem is the mileage of the injectors. In some cases, large mileage injector tends to inject far much more than normal. Therefore the ECU will correct the injection volume by dropping the injection time, reducing the calculated fuel consumption. However, you will see it on your gas exhaust measurement, normaly the Nox, COx and HC are exploding !

Well I will recommend you to have your electric system checked !

Regards

Jerome Douay

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Reply to
jejtopgun

It is really easy to figure out what is telling you stories.

Just fill it up and drive 100 km then fill it again to see what real life says to compare to the computer's BS.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

carl wrote:

Reply to
Mike Romain

Hi all,

I'm sorry I did not reply sooner.

Thanks for all of these replies.

As I stated, the fuel consumption at fill up is the same low level, and I am not sure that I checked against highway mileposts. But as the tach meter indicated only 10% off truth, I will have to check the odometer separately.

Today my valves were found to be a bit loose stemmed, but they were too tightly stemmed at the low level of consumption. And consumption has not gone up tremendously after the first correction nor the one today.

The spark plugs aren't showing lean mixture signs.

The ECU could be in error, but on the other hand, it has for every problem double checks, parameter checks and warning codes. None of these have been found pointing to something. A definite rarity indeed.

I will have to find a non-sceptical mechanic, who is willing to look and find ...

Thanks again for your replies.

Carl

Reply to
carl

Hi all,

I'm sorry I did not reply sooner.

Thanks for all of these replies.

As I stated, the fuel consumption at fill up is the same low level, and I am not sure that I checked against highway mileposts. But as the tach meter indicated only 10% off truth, I will have to check the odometer separately.

Today my valves were found to be a bit loose stemmed, but they were too tightly stemmed at the low level of consumption. And consumption has not gone up tremendously after the first correction nor the one today.

The spark plugs aren't showing lean mixture signs.

The ECU could be in error, but on the other hand, it has for every problem double checks, parameter checks and warning codes. None of these have been found pointing to something. A definite rarity indeed.

I will have to find a non-sceptical mechanic, who is willing to look and find ...

Thanks again for your replies.

Carl

Reply to
carl

did you turn the AC on?

Reply to
dojj

If everything else is OK, re-check your tire pressure.

Reply to
Bob Shuman

No. And it would rather push consumption upwards.

Reply to
carlvc

No. And it would rather push consumption upwards.

Reply to
carlvc

? huh

Reply to
dojj

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