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Here's the answer... (archive)

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by shawn anderson on November 04, 1999 at 12:38:03:

In Reply to: 5-speed owners, does your car do this? (Wierd...) posted by Tim Collins on November 04, 1999 at 00:40:10:

When you are coasting (say at 40 MPH) with the car in gear, the computer shuts off the fuel injectors to conserve fuel and uses momentum to keep the car running, so your MPG is basically infinity. When you take the car out of gear, the computer restores the gas supply to keep it running. This is what I heard from Brett Anderson (BMW Guru, if you didn't know) a while back, so the general idea must be correct.

: Ok, maybe I just have NO IDEA what the hell I'm talking about when it comes to car engines, but I've noticed a strange behaviour. Say I'm driving @ 40 MPH. I take it out of gear, and leave it in neutral, so it's just cruising and idling. I would think that the mpg needle would show the top, because I'm using just enough gas to keep a 700 RPM idle and going like 40 MPH, no? It doesn't. It is high, but not at the top. But if I have it in gear and just let completely off the gas, it DOES go to the top (highest MPG, no actual #). Why? Isn't it using more gas to maintain, say a 2500 RPM idle (if I leave it in 3rd) than a 700 RPM in neutral? So shouldn't neutral, 700 RPMs give me better mileage? I just find this really strange... can someone please explain this to me?!

: Thanks!

: Tim Collins
: '90 535i 5-speed sharked

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