increasing gas mileage?

[GoldenOne]

Almost two months ago my e34 died and i didnt have time or $$$$ to rebuild the engine. Found a used engine for $1300 with 76k miles on it, everything checked out, runs great but i noticed that on the obc the range counter starts to increase before it goes down. I.E. This morning I filled up and the range counter said i had +513 miles to empty. Hopped on to the highway cruisin at ~65mph and noticed that the range started to increase all the way to +543 miles. I thought it was suppose to go the other way. But then I increased speed to around 80mph and noticed that decreased to around +523 within 3-4 miles of going 80mph, then slowed down to 65mph again and the range went back up to +536miles. Is this thing adaptive to current speed? I cant truthfully say this happened with the old engine because I never noticed (or cared too)...

One other thing I picked up on is that the fuel gauge is a little deceptive. This a complete exaggerated example but its just to get the point across.
Having a full tank, I would drive to a certain destination and it says 3/4 tank left. It would sit for a little while and I start it up to go home. Now the gauge reads 1/2 tank. As I start out driving the needle will creep forward between 1/2 and 3/4......is there a part starting to fail?

[Qube]

Sounds about right. The gauge usually increases a bit when you start driving. I'm sure there's a reason like pressuring the tank or something I don't know... but it's normal. Can go from orange light to 1/4 tank at a cold start to warmed up.

[neil_004]

The range adapts based on average current consumption. If you drive the piss out of it for a while it will go down. If you have been driving the piss out of it and you get on the hwy for a while it will go up.
The fuel gauge operation is normal(at least on our 3 cars).
I've noticed that my fuel gauge is not linear. Hwy driving at consistant speed the first 1/2 goes by rather quick and the next 2 quarters are progressively slower.

[Qube]

Just noticed your question...


Is this thing adaptive to current speed?

Yes and no... it's adaptive on it's consumption calculation. Just like you see your 'current' consumption needle (under the rev counter, unless M5) move around when you drive, your 'range' will do the same accordingly.

In regards to the fuel gauge... trying to search... I know it's been discussed. In a nutshell, the there is smoothing involved. There is a float which gives rough indication of level, then some algorithm is applied to ensure your needle doesn't jump around at every hard corner you make... this basically slows down the response of your gauge. Something like that.

[BillionPa]

the gauge should be more accurate. I have a new fuel sending unit i need to install, and that is what reads the level. im just waiting till my fuel pump dies (knock on wood, thought it would happen a year ago!) to do it all at once.

[GoldenOne]

thanks for the advice guys! Now I know im not goin crazy, for a second I thought i was able spontaneously creating gas instead of consuming it lol ;)

[SnakeyesTx]

Mine drops almost a quarter tank less than what I have until I start driving. The reason this does this is because the inclines in the driveways you're parking into! It appears the sender is in the front right corner of the gas tank, which would be pretty sensitive to angled parking. Try parking backwards and you'll have a LOT mor gas registered than there is :D

As for the range thing, the computer factors this by your average mpg, which was probably climbing since your OBC was reset when you had the battery disconnected doing the motor swap. Its probably still settling into its moving average still. When I bought my car it was at 23 mpg, but the PO did a lot of highway driving. Since I reset the OBC, I have yet to get back up to that number (currently at around 19.8). You use less fuel at a steady cruising speed so its very possible that it will calculate higher mpg/range at 80 mph 3400 rpm, then while accelerating TO 80mph since the tach sweeps a broad range and the injectors dump a lot more fuel to meet the acceleration demand.