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  #1  
Old 05-16-2019, 05:26 AM
Frubbel1976 Frubbel1976 is offline
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Location: Belgium
 
Join Date: May 2016
Posts: 48
Mein Auto: X3 F25
Excessive mpg on acceleration/load

This going on for months now, realy frustrating... any help would be more than welcome:
When accelerating, even very slow on 1500rpm the instant mpg gauge (efficient dunamics) flips to the right, this isseu came overnight... there are no fault codes on ISTA+ all measurment from air intake-injection-exhaust-dpf are excellent after I managed the following:

-new injector
-air intake temp sensor
-new maf
-new air filter
-new diesel filter.
-cleaned swirl flaps and intake
-cleaned egr and egr-cooler
-....

The engine runs fine, no lack of power,...before someone reply's that the reaction of the mpg gauge is normal, I drived the car for over 200.000km and it has had never those sympoms before. I calcullated the mpg myself and its around 9l/100km before 7,5l/100km.

When cruising at contstant speed the mpg goes to the normal 6-7L/100km...

Thanks for your reply!!!
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  #2  
Old 05-16-2019, 02:41 PM
Doug Huffman's Avatar
Doug Huffman Doug Huffman is offline
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Location: Washington Island, Wisconsin, thru Death's Door
 
Join Date: Apr 2015
Posts: 12,973
Mein Auto: CPO2012 X5 35d M57(E70)
I believe that your instantaneous fuel efficiency gauge is NOW working properly.

Consider the gedankenexperiment; at a steady speed with a constant fuel usage efficiency indication briefly press the throttle to Wide Open Throttle and back to trailing throttle. You will see that distance (odometer) rate changes very slightly while fuel flow goes momentarily to maximum. Maximum fuel flow divided by a small change in distance is low, approaching zero, fuel efficiency.

I will make no attempt to explain your previous indications. Hand calculations are not instantaneous fuel usage rate. The Basic Computer instantaneous efficiency is only a guide to assist the driver evaluate efficient driving moment to moment.

Ask a physics calculus aware friend to explain it. In the final analysis there are functions that cannot be numerically integrated.
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Last edited by Doug Huffman; 05-16-2019 at 02:54 PM.
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Old 05-17-2019, 02:06 AM
glangford glangford is offline
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Location: US
 
Join Date: Dec 2013
Posts: 674
Mein Auto: 328d
My instantaneous mpg always goes over hard right on acceleration. What is important is the average MPG. It will go over hard right on acceleration then go all the way left on reaching cruising speed. Go up hill and it will to to the right, That's the way it works. And I routinely get around 60 mpg on my 328d on interstate driving. Around 38-40 in my mixed driving around town.
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  #4  
Old 05-17-2019, 07:27 AM
Frubbel1976 Frubbel1976 is offline
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Location: Belgium
 
Join Date: May 2016
Posts: 48
Mein Auto: X3 F25
To set things clear: mine is the European gauge; liters/km not miles/gallon...

Its NOT normal behavior since couple of months, its stays at max without moving when you push the gas, even when its in first and I don't accelerate the meter stays full ... the manual calculations are also bad.


I realy don't think BMW deliverd me a broken car that suddenly out of nothing is fixt now

I'm sure the DDE is providing the data for the efficient dynamics gauge, injection rate + speed.
Thought the speed was deliverd by the left rear abs sensor, but it does't. There is also a speed sensor in the ZF HP8 automatic transmission, but I'm not sure this is the one thats provide the speedinfo for fuel Calculation.

I realy think there is something wrong with the air intake, but all the tests with ISTA are telling me everything is ok (egr, swirls, throtle, bypass, turbo, maf,...).
OR there there's somewhere a sensor that does'nt give the right info... again all readings tel me there's nothing wrong.

This is the third BMW I own, the build quality is going down by every new model! I realy consider to buy a Cayenne Diesel, those are realy cheap in Germany for the moment (diesels can't drive in city's by new law) but I fix this one first...
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