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Discussion Starter #1
I have had my ca 2004 petrol 307 for about 2 1/2 years now, and it has recorded a fairly consistent 40 mpg average, which was only slightly more than I calculated myself based on fuel bought, miles driven. Recently, the computer suggested 45 mpg after a long road trip :), but now after re-zeroing everything this has reached 50 mpg (on the usual journeys) which I cannot believe. Presumably the flow sensor could be under-reading ?
Has anyone else encountered this and is there a self-fix (or at least diagnosis) available ?
 

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No fixes/calibration possible that i know of. There is no flow sensor, fuel use is calculated from engine ecu injection parameters so is only normally a good guess hence the longer distances logged the fuel figure becomes more realistic.

Often if car has been chipped with a tuning box then increase in fuel rail pressure (resulting in high volume of fuel used) is not detected by the ECU and you get "Improved" fuel economy.
 

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As Windy1603 says, no calibration possible. The trip computer MPG is merely a guide and can be wildly inaccurate. My first 307 regularly showed up to 72mpg when in reality is was at best 58mpg based on miles travelled starting with a full tank and the amount of fuel used to refill. My current 307 is slightly better in that it usually shows about 4 mpg less than the real mpg. I reset mine every week when I fill the tank and based on past readings, I have a pretty good idea of what the car is returning.
 

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Discussion Starter #4
Thanks for the info. The puzzle is why it should change so substantially, so suddenly - the 40 mpg is reasonably accurate given that I record my mileage & petrol purchase full-to-full. I would of course be delighted with 20% better fuel economy but seems too good to be true. The car appears to be driving much the same as before so I don't think the fuel injection system is misbehaving. More likely that the computer is on the fritz perhaps. All that was different before/after noticing this change was that I did a couple of 4-5 hour long journeys - perhaps 180 miles each way (slow roads)
 
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