The fuel rates computed (Instant and average) on my car are substantially inaccurate. I'm curious about how accurate most members' cars are, and am almost wondering if anyone even cares (except me).

Basically, it can tell me I did 21.5 MPG, but then I can drive 380 miles and put in 20 gallons of fuel. This is, in fact what I was seeing on my drive home when I bought the car, since I went for about a 3000 mile road trip at that point. My best tank according to the computer was 22.8 MPG, but I then put in 20.2 gallons of gasoline at the next station from when the low fuel message came up. Average speed was 74 MPH, distance driven was 406 miles.

This almost has me suspect an unmetered fuel source, but I would think that would show up on fuel trim (negative trim), but I haven't noticed it.

I had this happen on my old Cadillac and it turned out to be getting fuel into an evap line somehow at a bad in-tank assembly, which obviously would be dumped straight into the intake manifold just after the throttle body.