Instrument mpg etc is so far out!

[mgoode180566]

Phase 1 172. I cant get the mpg on the instruments to read over 12mpg ( struggle to get it close to double figures ) and of course the range is also miles out. I have run from full to full and the car is returning 32mpg which im happy with, it has donen this consistently recently.

What could be influencing the instrument ? Can it be resolved ?

 

[Vitor Alves]

Do you have any exhaust leaks?

I had a gradualy worsening exhaust leak in the header to cat joint section in my ph2 172. I think it was already slightly blowing when i bough it. In that condition my onboard computer readings where way too optimistic. The car would consume considreably more fuel in reality compared to the onboard readings. 3 to 5 liters more in reality. Was runing too rich i was told. Fooling the lambdas.

Now after fixing it, i got under the impression that the total consumed liters in reality and on the computer, are much closer. Last time i checked at fill up tim,e was only about 1 liter in difference i think.

And the liters per 100kms average now seems to vary acordingly to my driving. Before it was always close to 8.1, as i remember. it just didnt vary much. Its af if the onboard computer displayed values where not taking into account the fueling diference caused by the pre lambda leak?