Odd behavior then. On my old turbo diesel VW, what you describe would be called "limp mode" where the engine management system defaults to air and fuel flow that will definitely work but leaves the car feeling like a limp noodle on the road and get very poor economy.Hello,
I have done it both ways, and find the trip computer fairly accurate. I am using premium (93 oct. Mobile) and it does not look they topped off the tank. The weather is a bit warmer recently than it was before the ECU update.
In any case, I see the numbers improving recently. I think the issue was : the ECU update resets to factory defaults. It looks like, it takes some time for the computer to re-optimize its settings based on observed data. I have now 150 miles racked up since the update, and I am almost back to where I was before. (Getting close to 38mpg on hwy now).
I would be really interested in what kind of experience other folks had, who had the ECU update done.
I guess this might also explain why the first fuel tank in my car was only able to get me about 2/3 of the distance the tank gets now. It must have been learning then too.