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Thread: Poor fuel economy ( help please )

  1. #26
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    Quote Originally Posted by Timm View Post
    When the engine is at running temperature the pre-cat O2 sensors should be swinging around the scale - the O2 sensors are narrow-band devices and can only detect if the mixture is too lean or too rich (unlike wide-band O2 sensors which provide a linear reading of oxygen levels).

    The DME is constantly adjusting the fuel/air mixture - it increases the fuel when the O2 sensor shows the mixture is too lean and reduces it when it detects the mixture is too rich - it does this constantly so the O2 voltage swings around. The adjustments are quite small - but the O2 sensors are very sensitive.

    The integrated Lambda reading is the filtered and integrated Lambda reading and gives a true reading of the average fuel/air mixture - it is that value that is worth watching - all explained here:

    https://www.meeknet.co.uk/E38/Diagnostics.htm

    I read the inpa values today it was -7 in additive in both side , zero in multiplicative in both sides


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  2. #27
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    I can't remember who I am answering but:

    -7 on additive adaptations is fine (as long as you have let the engine run long enough for the adaptations to have settled)

    If your O2 sensor readings (raw value, not the integrated value) don't move then either the sensor has failed OR the mixture is too far out for the DME to correct with adaptations - you will get an 'adaptations have reached limit' error.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #28
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    Quote Originally Posted by Timm View Post
    I can't remember who I am answering but:

    -7 on additive adaptations is fine (as long as you have let the engine run long enough for the adaptations to have settled)

    If your O2 sensor readings (raw value, not the integrated value) don't move then either the sensor has failed OR the mixture is too far out for the DME to correct with adaptations - you will get an 'adaptations have reached limit' error.
    I see today the engine temp 73c which raise to 80c max , I think its thermostat, The poor economy ( 6 km /l) highway is related to temp ?


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  4. #29
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    Yes, that's a bit low for an E38 - with the mapped thermostat you are usually around 105C at idle - but as you get the mapped thermostat error I guess it has been removed or replaced with a fixed stat....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  5. #30
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    Quote Originally Posted by Timm View Post
    Yes, that's a bit low for an E38 - with the mapped thermostat you are usually around 105C at idle - but as you get the mapped thermostat error I guess it has been removed or replaced with a fixed stat....
    Which is better the 105 or the thermostat with spacer 80 ,88c ?


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  6. #31
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    Quote Originally Posted by haydar alameen View Post
    Which is better the 105 or the thermostat with spacer 80 ,88c ?


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    Stick with the stock 105c tstat if you want the best MPG...

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  7. #32
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    Quote Originally Posted by purplecty View Post
    Stick with the stock 105c tstat if you want the best MPG...

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    My thermostat is stuck opens , I purchased a thermostat spacer as I read the 105 c is too high ( in Simmer the fuel is boiling in the tank when gets above 100c ) so what lower temp is best ? 85 , 88 , 95 ? No much difference in mileage


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  8. #33
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    An open thermostat will certainly increase fuel consumption as it will take forever to get any heat in the engine. 85C or 95C, either will do - but no thermostat will cause engine damage.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  9. #34
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    Just a random thought to throw in - it's possible being Iraq that his car was delivered with the factory hot climate package? I got that here in Australia which meant a factory 80c thermostat... Even on 35c+ days I never see it go past 80c, it works remarkably well. Unless it was an import, in which case never mind!

  10. #35
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    Quote Originally Posted by Sobek View Post
    Just a random thought to throw in - it's possible being Iraq that his car was delivered with the factory hot climate package? I got that here in Australia which meant a factory 80c thermostat... Even on 35c+ days I never see it go past 80c, it works remarkably well. Unless it was an import, in which case never mind!
    True i think they call it GULF version on realoem?

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  11. #36
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    Quote Originally Posted by Sobek View Post
    Just a random thought to throw in - it's possible being Iraq that his car was delivered with the factory hot climate package? I got that here in Australia which meant a factory 80c thermostat... Even on 35c+ days I never see it go past 80c, it works remarkably well. Unless it was an import, in which case never mind!
    Unfortunately it's Euro version


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  12. #37
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    poor fuel economy ( help please )

    Updated , I installed the stock thermostat , o2 sensors ( used I have previously ) the fuel economy is better city 11-12 mpg (4.5-5 km / l ) highway 17-20 mpg , thank you all , I also want to search for other causes as it's a bit lower than normal , this is the adaption values after 65 km run ( the engine is off )



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    Last edited by haydar alameen; 11-24-2018 at 02:51 PM.

  13. #38
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    Those values are fine, nothing to worry about, so if you have poor economy then the air/fuel mixture is not the problem.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  14. #39
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    Quote Originally Posted by Timm View Post
    Those values are fine, nothing to worry about, so if you have poor economy then the air/fuel mixture is not the problem.
    Thanks Timm
    So what are else ?
    And what is the estimated mpg for this car 280k km


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  15. #40
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    Quote Originally Posted by purplecty View Post
    Stick with the stock 105c tstat if you want the best MPG...

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    now I use the stock thermostat, the mileage is better about 18mpg us highway . But I noticed the coolant is decreasing each 2 days about 1 liter ( only water I filled ) previously no or very little amount decreased when the open thermostat is in . No obvious leak


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  16. #41
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    Quote Originally Posted by haydar alameen View Post
    now I use the stock thermostat, the mileage is better about 18mpg us highway . But I noticed the coolant is decreasing each 2 days about 1 liter ( only water I filled ) previously no or very little amount decreased when the open thermostat is in . No obvious leak


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    Thermostats dont eat coolant. Make sure you top it off properly after the car has sat for over 15 hours in hot weather or at least 8 in cold weather...

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  17. #42
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    Yes surely , I mean the 105 c degree which is higher than water boiling may cause evaporation of water or some thing like this ?
    Do you mean re bleeding when cold ?


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  18. #43
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    Quote Originally Posted by purplecty View Post
    Thermostats dont eat coolant. Make sure you top it off properly after the car has sat for over 15 hours in hot weather or at least 8 in cold weather...

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    Yes surely , I mean the 105 c degree which is higher than water boiling may cause evaporation of water or some thing like this ? also I notice the hoses have high pressure ! Is it normal for 110 c ?
    Do you mean re bleeding when cold ?


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  19. #44
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    The cooling system is a closed, pressurised system - and although temperatures may reach well over boiling point of plain water the system is filled with coolant which has a higher boiling point. More importantly the system is under pressure (maximum 2-Bar) and that raises the boiling point significantly.

    More info here:

    https://www.meeknet.co.uk/e31/BMW_M6...ing_System.htm
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  20. #45
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    Just top it off correctly after it sits overnight to get it propeely filled. Dipstick tip should be even with the opening of the expansion tank lip...

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  21. #46
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    Regarding economy , Timm said that it is not fuel air mixture problem so what else ? , I calculate it more accurately it is 14 L/ 100 km highway , 23 L/ 100 km city , at constant speed 80km/hr the eco 9 L / 100 km , @120 km/hr is 12 L / 100 km , all these records in normal style driving . The idle is low ~500 rpm
    These last inpa data with recent adaption ( both banks was additive -2 multiplicative -3 . Air intake was low ! ~16 IMG_0845.jpgIMG_0846.jpgIMG_0847.jpg


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  22. #47
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    Clogged cat ???


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  23. #48
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    Yes, that or dodgy petrol!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  24. #49
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    Quote Originally Posted by Timm View Post
    Yes, that or dodgy petrol!
    How to diagnose the bad cat. , and can be cleaned ?


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  25. #50
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    A garage can check the back-pressure at the Lambda sensor points
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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