Gas consumption meter

[Bo525i]

Is my gas consumption meter wired wrong or something?

When I drive it shows the l/100kms (euro car) as it should but when I slow down to near nothing or make a halt it goes beyond the 30l/100 mark and hides (white arrow on pic), thats the opposite of the 0 mark!

I find that kinda wierd if its normal and it actually screws with the averages measured by the obc..

[repenttokyo]

totally normal behaviour - if you aren't moving, then you are diving by zero....so there's no fuel efficiency to show. an engine is least efficient when idling.

it doesn't 'screw' with the averages on the obc - the fact that you are burning fuel and not moving means your average fuel economy goes down....

[Bo525i]

Thx for clearing this up for me!

"it doesn't 'screw' with the averages on the obc"
Well it does actually, lets say I start up a new average measure in idle before leaving for work, then quietly roll off with a very light foot, I then see the obc telling me that I´m using +30l/100 and dropping for like 10-15 mins till I´ve been on the freeway for some time and the values settle around 11-12l/100 so it does affect the measurement during that whole trip because of the "beyond" 30l/100 position.. Now if I clear the values during the trip, just before or on the freeway my average will be 8,8 or so even at high speeds

Details I know, but still

[Paul in NZ]

Dont start at rest then.Start a new measure when the car is warm too,because cold running is rich running.My average has dropped slightly lately,because its colder and i now have a shorter trip to work,so the cold running is now a bigger proportion of my trip.

[BradHouser]

Is my gas consumption meter wired wrong or something?

When I drive it shows the l/100kms (euro car) as it should but when I slow down to near nothing or make a halt it goes beyond the 30l/100 mark and hides, thats the opposite of the 0 mark!

I find that kinda wierd if its normal and it actually screws with the averages measured by the obc..

The gauge doesn't screw with the averages: stopping changes the averages.

If you aren't moving you are getting zero MPG, or infinite l/100 Km. Average MPG is Total Miles divided by Gallons, or in your case, Total Liters, divided by Total Hundreds of Km. (remember your Algebra?)

The OBC has only to keep track of liters used and miles driven to calculate the average, by dividing one by the other (depending on which unit, Metric or US, is used).

If the OBC used the gauge as input, it would have to integrate the instantaneous readings over time, clearly a much more complicated and unnecessary calculation, plus it would require enough memory to store every data point, which would eventually fill up and rollover and not be a true average. (Remember your Calculus? No? Integrating is calculating the area under a curve, liters = f(km) or gallons=f(miles).)

[repenttokyo]

Thx for clearing this up for me!

"it doesn't 'screw' with the averages on the obc"
Well it does actually, lets say I start up a new average measure in idle before leaving for work, then quietly roll off with a very light foot, I then see the obc telling me that I´m using +30l/100 and dropping for like 10-15 mins till I´ve been on the freeway for some time and the values settle around 11-12l/100 so it does affect the measurement during that whole trip because of the "beyond" 30l/100 position.. Now if I clear the values during the trip, just before or on the freeway my average will be 8,8 or so even at high speeds

Details I know, but still

that's how averages work, man.

[Bo525i]

Sigh! So an average of 0 isn´t really 0..

Let me reverse the facts, I´m riding calmly @ 70 mph on the freeway.. Comsumption is 8,8/100, I now decide to recalculate, keeping speed.. I press the calc and 3 mins later I let go of the acc entirely.. warm engine, no speedups, no real fuel consumption compared to 70 mph,.. the meter passes 30l/100, the OBC registers that fact and I come to a halt, still haven´t touched the acc and I switch off!
Now my consumption shows around 28l/100 so I actually use more gas in idle and with the engine off than @ 70 mph


Mind you, that this is only happening with a freshly started consumption calc.. And I´m just kidding really

Topic answered, my meter´s fine.. Thx!

[kev535i]

my gas gauge looks like this

[bubba966]

Let me reverse the facts, I´m riding calmly @ 70 mph on the freeway.. Comsumption is 8,8/100, I now decide to recalculate, keeping speed.. I press the calc and 3 mins later I let go of the acc entirely.. warm engine, no speedups, no real fuel consumption compared to 70 mph,.. the meter passes 30l/100, the OBC registers that fact and I come to a halt, still haven´t touched the acc and I switch off!
Now my consumption shows around 28l/100 so I actually use more gas in idle and with the engine off than @ 70 mph

No, you're not using more gas at idle than you are at 70 mph. You will run out of gas quicker doing 70 than you will sitting and idling.

But, after going through a tank of gas doing 70 how many km did you cover? At 8.8/100km you should've gone 860km. And it would've run you dry a little over 7 hours.

If you go through a tank of gas just sitting there idling and going nowhere how far did you go? 0km. No clue how long that'd take, but it'd be a good bit longer than 7 hours.

Now do you see what your gas consumption gauge is telling you? It's telling you how much gas it takes to cover a certain distance, not how much gas you're using per hour.

Oh, and the OBC average isn't real time unfortunately. It lags a few minutes behind what you're actually doing. So if you drastically change the fuel consumption it'll take a few minutes for that to effect the OBC average.

And that lag can make it really odd sometimes. Occasionally I have fun with the range display and see how much higher I can get the range to read after I've traveled a certain distance. Like when it says I've got 403 miles before the tank's dry. Then I drive 25 miles and it says that I've got 465 miles left before the tank's dry. I increased my MPG so much by driving differently that it raises the average MPG a good bit. And as it's got that lag in the OBC when it calculates the average I've seen it many times continue to go up even as I've sat idling for a minute or two. As in I got stopped at a long light and I've got 464 miles left. Then after idling for a minute or so I've got 466 miles left. I didn't just gain two miles of range by sitting there idling. But due to the lag in the OBC it seems like I had.

[repenttokyo]

No, you're not using more gas at idle than you are at 70 mph. You will run out of gas quicker doing 70 than you will sitting and idling.

But, after going through a tank of gas doing 70 how many km did you cover? At 8.8/100km you should've gone 860km. And it would've run you dry a little over 7 hours.

If you go through a tank of gas just sitting there idling and going nowhere how far did you go? 0km. No clue how long that'd take, but it'd be a good bit longer than 7 hours.

Now do you see what your gas consumption gauge is telling you? It's telling you how much gas it takes to cover a certain distance, not how much gas you're using per hour.

.

interestingly, if you unlock your OBC, you can get it to display the liters per hour you are using, like a jet. I think it's function 4.