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I have noticed that if I take my foot off the accelerator whilst traveling at speed the instant mpg gauge goes up to just above 50 mpg. Then after approximately a 1 second delay the mpg goes right to the top of the scale.

I'm sure this behavior is quite normal but I just wanted to confirm a hunch with others here...

I'm guessing that the ~1s delay I see is how long it takes for my VANOS to adjust the timing for the optimum fuel efficiency.

Is my hunch right or is the delay caused by something else i.e. how long it takes to use up fuel in the injectors?

Anyone else noticed this?

Just curious to know the cause.
 

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I Am The Machine
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I believe its from the injectors. I don't think Vanos would cause that to show up, although you would drop the vacuum in the manifold so that could be as well.

However, above a certain RPM (I think its around 1200 on BMWs) the injectors shut off, which it sounds like you know. So basically the car isn't using a drop of fuel. It has a small delay, of course, so the injectors don't shut off every time you take your foot off the gas to shift. Pretty sure that accounts for the pause.
 
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