Quote:
Originally Posted by JockoT
I know my ScanGauge does not give me a definitive mpg but it does show me if what I am doing is better than worse than what I was doing before.
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Not really. When you calibrate your OBD gauge, you're basically telling it 'here is my fuel consumption for the average engine speed/load over the last tank'.
I've had my SG2 for around six years and I don't think I've ever had the calibration be within 2% on consecutive tanks - it's quite typical to be out by +/-5% (ie a 10% error spread). Highway drivers will have a smaller discrepancy because they're average speed/load is more consistent. But when you change driving style you throw calibration out the window to a large extent.
When you accelerate, your AFR turns slightly rich (acceleration enrichment), even if you car stays in closed loop, the only way to accelerate is to run slightly rich. This is almost certainly enough to counter the 2% gain the SG reports.
The SG2 is broadly useful in many respects, but it falls down on really fine tuning driving style. I use the onboard display for IC in my Renault as it does account for the AFR, and the SG2's short trip as an indicative game.
I just fitted an MPGuino - that does measure fuel and therefore enrichment - to my Proton. I'll try Pulse and DFCO while I zero in on it's ideal driving style, but from memory when I last used it, I don't think it was accurate tank to tank to within 2% either.