Date: Sun, 02 May 2004 23:12:21 +0100
From: Colin Stamp <>
Subject: Re: Fuel consumption figures computer wrong

On Sun, 2 May 2004 08:02:25 +0100, David Taylor <> wrote: >> That's why I said it wouldn't be perfect, but more than 6 litres is >> still an awful lot to be out by. It'd probably fill up the tank filler >> pipe several times over! > >Do Saab provide a calibration certificate for the computer or the >components in its constructions? > >I don't have one! :) > >What's the calibration and component error there? It's true, it's not exactly a major fault or anything, but it is interesting if you're a bit of an instrumentation nerd. The problem won't be with the computer - that just needs timing accuracy which'll be measured in PPM rather than percent. The speedo measurement will cancel out because it's used in both manual and computer calculations. That leaves us with the petrol station vagaries (for the manual calculation) and the assumptions the computer has to make about fuel flow through the injectors. Any filling foul-ups should become apparent at the next visit to the money pit so, if the difference between the manual and computer figures is consistent, we can assume it's the computer that's wrong and it's down to the assumed fuel flow rate being wrong. Anyone still awake and reading by this point will twig that this means the SID is actually, in a really roundabout way, telling us something worthwhile(!) - the fuel flow through the injectors is different from SAABs expected figure. Others have said their readings tally up, so it looks like SAABs figures are reasonable and there must be a difference with our particular car. Who knows, correcting the error may actually improve the fuel consumption for real ;o) Colin.

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