E46 runs out of gas

"Jeff Strickland" wrote

Just curious, what does the analog fuel gauge show when there's 30 miles remaining? Is it already rested against the left limit or not quite?

Pete

And at what point does the fuel reserve icon come on? On my '99 E46, reserve comes on with almost exactly 2 gallons remaining, so I have 40~60 miles, depending on traffic & road conditions to find a station. I've also noticed that the range to empty on every BMW car (and motorcycle) I've owned is non-linear below 100 and can drop from 80 to 50 in only 3 or 4 miles. Sounds like your daughter should fill up at no less than 1/4 tank to be on the safe side.

Tom K.

Good question, I don't know. I'm not sure how that helps though.

She is driving along and the car reports via the gas guage that she needs to make a pit stop soon. She hits the Range button, which reports that she has

50 or so miles to go. Eventually it reports 30 miles to go, but shuts down because there is no fuel remaining.

We get the whole idea that she needs to buy gas about 15 driving minutes or so earlier than her current schedule, but if the car is telling her that she has n-miles to go, and the motor dies in a few yards, it seems that the Range feature is a bit out of calibration and is pretty much useless. Our other car seems to do a much better job of reporting how far the car can be driven before one lace up the shoes and hit the bricks.

It is possible there is about 1 gallon of water or other non-combustable in the tank. I would let her run it out of gas and then be sure the tank is, in fact, empty of everything.

It would be a b****r to start if water got in the fuel line...

"Jeff Strickland" wrote

It helps you diagnose whether just the on-board computer is wrong, or whether the gauge gets the same faulty reading and shows that some gas is still remaining in the tank while it isn't. If both are wrong, it may be a faulty sensor/fuel sender unit.

If it's just the on-board computer, then AFAIK, the way it reports "miles to empty" can be adjusted.

Cheers, Pete

The function used to determine remaining mileage is almost certainly at least partially based on (and weighs heavily) the current rate of consumption. I've verified this numerous times by driving for a good distance (20+ miles) on a freeway (constant speed, say 65MPH) then getting off and seeing an immediate decline (this is in my '03 330Ci). I've watched the remaining MPG drop by about 9 miles over the distance of an offramp and a few hundred yards. The system is not entirely memoryless (obviously it uses some algorithm to make an estimate on remaining mileage when the car is turned on/filled up), but I highly doubt this goes beyond the previous few fill-ups.

Well I think the most obvious question you need to determine is when she fills up the tank when it's empty (but claims to have miles remaining), does the amount she fills match the cars rated capacity (about 16 gallons in mine). Considering it's potentially a difference of 30 miles (roughly a gallon), it should be fairly obvious whether there's a physical obstruction (eg. some non-combustable fluid). In fact, I'd be using the odometer to check if the MPG she's getting is within reason (assuming normal driving habits, if it differs more than 10% of what the car's rated, I'd be concerned).

I think the other part of the equation that folks are missing is the range is determined based on the fuel gauge sensor. If that is off by a little, so will the range.

This is from the Owner's Handbook from my new 335d coupe.

"The (range) display indicates how far the car can probably be driven on the fuel remaining in the tank. The range is calculated on the basis of the way the car has been driven over the past 20 miles, and the amount of fuel currently in the tank."

There then follows this warning:

"If the remaining operating range is below 30 miles, it is imperative to add fuel, otherwise the engine's functions are not assured and damage may occur"

Hope it helps,

Vijay

I suspect there is no water in the tank.

The water would be at the bottom, where the fuel pick-up is located, so the water would be present regardless of the tank being full or empty, AND the water would be evacuated over time (assuming the motor would run as it sucked the water from the tank). Since the car has no driveability problems at any other time, I sleep easy knowing there is no water in the tank.

In other words, subtract 30 miles from whatever it shows to see the real (safe) miles-to-go. Makes you wonder how accurate these things really are.

I miss the old half(?) gallon reserve trap in my Triumph Vitesse, where you could run out then open the boot and turn the reserve valve lever and get going again, knowing pretty much how soon you needed to get more. Not that I made regular use of it, but it did remove pretty much all of the doubt.

Still widely used on motorcycles.

As accurate as any AVERAGE can be.

The gauge (gage) is damped and reads the average condition as the fuel slops from side to side - back and forward.

Hence the computer reads the fuel being used - sent to injectors less that returned to tank and calculates what the mileage would approximate to.

However - WHY THE HELL do you let your tank run dry - think of all the shit the pump might pick up let alone the aggravation of walking to the next gas station.

Twit is a word that springs to mind for anyone that lets the gas tank get so empty..................

Actually you would save money by keeping it as full as you can as less space for it to evaporate.

Sir Hugh of Bognor

The difference between men and boys is the price of their toys. Intelligence is not knowing the answer but knowing where and how to find it!

Hugh Gundersen snipped-for-privacy@h-gee.co.uk Bognor Regis, W.Sussex, England, UK

No - it simply computes the tank contents - given by the fuel gauge - against the instantaneous fuel consumption - given by injector opening and speed/distance sensor.

Most likely fault is the fuel gauge sender in the tank.

Actually, it seems the fuel consumption is a buffered average of some sort as the range does not vary immediately when you accelerate or decelerate. It takes a while after a change in driving style before the range changes. But it will not retain that average for very long, such as from a previous driver.

I was referring to the 'miles till empty' - and that does react quickly especially when the fuel is low. A cold start followed by gentle driving will show it count *up*...

I do not let MY tank run dry, but thanks for the insult.

The tank CLAIMS to have more than enough gas to get to the gas station, but is apparently lying when it maks the claim.

Twit is a word I'm thinking of right about now as well. I'm thinking of empty too, but not the gas tank.

I was too, and that hasn't been my experience.