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Thread: Poor fuel economy ( help please )

  1. #1
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    Poor fuel economy ( help please )

    Hello every body , my car ( e38 1997 740 eur ) has poor fuel economy with moderate driving . city 4 km / l , highway 6.5 km /l
    no errors except for map cooling , bank 2 o2 sensor .
    maf , injectors , plugs purge valve , fuel filter , fuel pump and engine gasket are replaced with no change

    I have rough cold start with low power but its fine when get hot . only fine roughness at idle and sometimes tiny hiccup at rpm 2k when car in parked otherwise the acceleration is very good . I upload some pic from inpa , smoothness is shown to irregular I switch off the coils and no change .
    45956513_1146086855550439_5386700768067715072_n.jpg
    45959566_1283406045133170_2721426222323073024_n.jpg
    45966161_1027971284048169_7572126260239794176_n.jpg
    Last edited by haydar alameen; 11-11-2018 at 05:00 PM.

  2. #2
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    A bad thermostat and upstream o2 sensors can lead to bad MPG. Bad intake gaskets can also potentially cause false o2 errors from the additional air it is pulling in before the engine gets hot and expands the gasket a bit. I had a bad cold start idle and an intake reseal resolved that. All new intake gaskets and TB gasket. Might consider doing the valley pan while the intake is out too...

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  3. #3
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    Your adaptation values do not support an O2 error - unless you have cleared adaptions just before you took the screenshots, or, the O2 sensor is dead. What was the O2 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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  4. #4
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    poor fuel economy ( help please )

    Quote Originally Posted by purplecty View Post
    A bad thermostat and upstream o2 sensors can lead to bad MPG. Bad intake gaskets can also potentially cause false o2 errors from the additional air it is pulling in before the engine gets hot and expands the gasket a bit. I had a bad cold start idle and an intake reseal resolved that. All new intake gaskets and TB gasket. Might consider doing the valley pan while the intake is out too...

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    Thank you Purplecty
    Regard o2 sensors previously I had 2 working sensors and the problem still
    , can I use some sort of sealer rather than new gasket ?


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    Last edited by haydar alameen; 11-11-2018 at 11:57 PM.

  5. #5
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    poor fuel economy ( help please )

    Quote Originally Posted by Timm View Post
    Your adaptation values do not support an O2 error - unless you have cleared adaptions just before you took the screenshots, or, the O2 sensor is dead. What was the O2 error?
    Thank you Timm
    I am thankful for you regard your site and the huge information in it .
    Recently I did adaption but previously the additive not fixed I saw it -2 and +2 from different times, multiplicative is -4 or near that value


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  6. #6
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    I would guess then that the O2 error was not an 'adaptations at limits' and is a real O2 error. In which case, as purplecty says - you won't get good MPG until that problem is fixed by replacement of the Lambda sensor...
    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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  7. #7
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    Quote Originally Posted by Timm View Post
    I would guess then that the O2 error was not an 'adaptations at limits' and is a real O2 error. In which case, as purplecty says - you won't get good MPG until that problem is fixed by replacement of the Lambda sensor...
    My o2 sensor is Bosch , but for e34 I transfer the connector , I can see it goes up and down by inpa ! .
    If the vac leak with in adaption limit the car can run smoothly with no effect on economy ?


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  8. #8
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    All explained here:

    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. #9
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    Here is the gasket


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  10. #10
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    Quote Originally Posted by haydar alameen View Post
    Here is the gasket


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    Replace all of them even the ones on the front and rear and the throttle body one as well...
    https://www.fcpeuro.com/products/bmw...et-11611433328

    https://www.fcpeuro.com/products/bmw...et-11611729728

    https://www.fcpeuro.com/products/bmw...or-11611729727

    https://www.fcpeuro.com/products/bmw...et-13547510433


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    Last edited by purplecty; 11-12-2018 at 02:43 PM.

  11. #11
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    Any luck?

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  12. #12
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    Quote Originally Posted by purplecty View Post
    Any luck?

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    Thank you my friend,
    I removed the intake manifold and replace the gaskets the engine runs better but economy is the same ( I install universal Bosch o2 sensor at the same time , may be problem with it !


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  13. #13
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    Update , It was the manifold gasket which cause poor power and rough idle , economy is still and I will give you feedback


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  14. #14
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    Why universal o2s? The direct fit bosch ones are cheaper and plug and play...

    https://rover.ebay.com/rover/0/0/0?m...2F252282318699

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    Last edited by purplecty; 11-16-2018 at 05:38 PM.

  15. #15
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    Quote Originally Posted by Timm View Post
    All explained here:

    Thank you Timm
    I saw your videos previously , its simple and very informative .
    Regard the o2 sensors it should be oscillating on inpa or not , I use the reading of l/ h from test 4 and I see there is no correlation with voltage changes of the sensors in inpa !


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  16. #16
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    poor fuel economy ( help please )

    Quote Originally Posted by purplecty View Post
    Why universal o2s? The direct fit bosch ones are cheaper and plug and play...

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    Unfortunately I do not get it I lives in Iraq


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  17. #17
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    Quote Originally Posted by haydar alameen View Post
    Unfortunately I do not get it I lives in Iraq


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    Oh ha woops didn't recognize that... So the intake gaskets resolved the cold start idle?

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  18. #18
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    Quote Originally Posted by purplecty View Post
    Oh ha woops didn't recognize that... So the intake gaskets resolved the cold start idle?

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    Yes


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  19. #19
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    Quote Originally Posted by haydar alameen View Post
    Yes


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    Great! Did you reset adaptations after installing the o2s?

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  20. #20
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    Quote Originally Posted by purplecty View Post
    Great! Did you reset adaptations after installing the o2s?

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    Surely yes


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  21. #21
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    Quote Originally Posted by haydar alameen View Post
    Surely yes


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    Keep us posted...

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    Quote Originally Posted by haydar alameen View Post
    Thank you Timm
    I saw your videos previously , its simple and very informative .
    Regard the o2 sensors it should be oscillating on inpa or not , I use the reading of l/ h from test 4 and I see there is no correlation with voltage changes of the sensors in inpa !


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    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
    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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  23. #23
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    Quote Originally Posted by purplecty View Post
    Keep us posted...

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    Ok I will do this


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  24. #24
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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
    Ok . So if the reading is fixed at for example 0.50 it means not working sensor ?


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  25. #25
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    Quote Originally Posted by haydar alameen View Post
    Ok . So if the reading is fixed at for example 0.50 it means not working sensor ?


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


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