Fuel tank range reads +300

[bimmer630]

so BMW tank range logic is crap? (at least on old cars) sounds like alot of you guys are running an OBC that came in your car, with no engine mods, and they still dont estimate tank range correctly?

[nando]

the OBC and range feature works fine. most people just don't know what it means, or how many gallons are in their tank, or what the R and the little orange light actually mean.

[nando]

What does the reserve light look like when it comes on? I gotta pull my cluster this weekend and fix my gas guage, My pump likely hates me: I have been driving everywhere with just $20 in the tank. FML

it's just an orange light right next to the R.

[delatlanta1281]

so BMW tank range logic is crap? (at least on old cars) sounds like alot of you guys are running an OBC that came in your car, with no engine mods, and they still dont estimate tank range correctly?

Remember, this was a LUXURY back in the 80s. Very few cars had these options, and being somewhat new technology, i would expect that it wasn't as cutting edge as it is by today's standards. That being said, cars age, internal parts age and become less efficient. I doubt BMW was planning on letting a bunch of kids know what their milage per tank would be 25 years later. Do it the old fashioned way and fill up, then calculate per trip. If you don't want to do that, sell or R3V your car, then buy a new Honda.

[nando]

it works fine. The only thing that would cause it to be less accurate would be injectors that are clogged, fouled, or stuck, a big dent in your fuel tank, or level sensor that doesn't work anymore. all a possibility, but the's nothing inherently wrong with the system.

[delatlanta1281]

So it is constantly calculating, then recalculating due to fuel level vs mileage?

[nando]

yes

[Laura]

Mine shows 425+ and the light comes on whenever I get to around 36m left, one day I drove it till it showed 6m lefts and then showed -----, but I was able to get to the gas station without a hitch. It's a 325i and the highest I get is 360 miles on 1 tank.

thats exactly what mine says. shows ----- after 9 miles though instead of 6.

[ohthejosh]

when I drove to LA I had my GPS going at the same time and the GPS shows how miles till my destination and my OBC was verry accurate maybe give or take 10-15 miles depending on how you drive.

[quikveedb2]

My OBC shows roughly 30 miles left in my tank when my reserve light comes on depending on the slope of the road. "30 miles" works out to be about 10 miles of city driving, and I've never tried to push it past the limit on the highway. Just get gas when the light comes on, if it works, or more often if you're worried about your fuel pump.

[Vtec?lol]

Seems pretty normal. Most E30's, when the obc reads 40, you need to fill up. 30=0 miles left.

Make sure the tank isn't dented like nando suggest.

[leothedrummer]

yeah, they never got 0 miles. thats why you should put a can of fuel in the trunk and drive will you run out of gas so you know where the needle/OBC stops when you have absolutely nothing left. or just fill it up when you get to 1/4 of a tank to keep your pump cool.

If I've been giving the car a bit of a thrashing on a low tank of fuel, the OBC in my M535i often reads blank.

And when it comes to knowing how much fuel you really have in the tank, the best way will also be to get a rough estimate with the trip meter.

[long tall eta]

guys, stop running your tanks that low. u have any idea how much crap can accumulate in there in 25 years???????? u really wana suck that through your lines???

and oh yea, never run it up the spout either. bad for the level sensor

[dogsbark26]

Both the econometer and the OBC must depend on the ECU to make their calculations of MPG and thus, fuel economy. My guess is that the ECU (and so the econometer and OBC) base the calculations on the duration of the fuel injector pulse length.

Therefore, because I have installed larger than stock fuel injectors, the chipped ECU requires a shorter injector pulse causing the econometer and OBC to "think" I am getting better MPG.

It would require greater knowledge of electronics than I possess to alter those electronics for an accurate reading - or even to figure out which electronics need to be altered for a more accurate reading. That being said, the readings can still be useful if, as previous posters have pointed out, you familiarize yourself with the relationship between whatever readings are displayed and the reality you can prove. i.e. When it says I have 52 miles left, I really have only 34. Or when it says 20, I will run out of gas.

[MAXELHOFF]

Uh huh

Sooooo. Light on=get fuel. Thanks! Free image.