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  1. #1
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    735i high consumption


    Hello, '88 735i, runs smooth, no fuel smell from tail pipes at idle, very high fuel consumption - around 27L/100 km. OBD TEST03 reports 4.2L/h... Car has no cat ( euro version ) and no O2 sensor, engine harness has a OEM rubber cover on the O2 sensor socket. Checked: distributor, TPS, temp sensor, changed spark plugs and wires, air and fuel filter, swapped AFM . Not checked fuel injectors and fuel pressure. However, the car has sequential LPG installed and the LPG consumption is also very high, almost double as it should be. The sequential LPG installation uses its own injectors this is why I do not suspect gas injectors / fuel pressure / regulator to be the source of the problem.


    Quote : "Patrick C 88 750 159K on 2007-05-01 at 22:33:55
    Inside the DME there is a small circuit at the input of the O2 sensor signal that loosely keeps the input at 0.4V or so if O2 sensor is not connected. If the O2 sensor is cold, the high internal impedance also makes it behave as if it is not connected.
    If your DME sees 0.1V or 0.8V staying for over some time (90 seconds?) it will flag a CEL. Here the input voltage never swing to either side so the DME is happy.... "

    I suspect a faulty DME, because even without the O2 sensor the DMW will use a default value instead of missing signal from the oxygen sensor. Running with a missing or disconnected sensor will give you a worse mileage but not as bad as I have.
    The question is: except the DME, what else should I check? Any suggestion is appreciated. Thank you. Mihai G.

    '91 BMW 850iA (Mauritius Blau 287)

    '91 BMW 750iL (Islandgrun-metallic 273 ) ( euro )
    '91 BMW 735i ( Mauritius Blau 287) ( euro )
    '89 BMW 735i ( Delphin Metallic 184 ) ( euro ) & LPG
    '89 BMW 730i ( Islandgrun-metallic 273 ) ( euro )
    '05 Peugeot 407 SW (Dolomites)


  2. #2
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    Replaced DME

    but no improvement...And now what? :-< Mihai G.

    '91 BMW 850iA (Mauritius Blau 287)

    '91 BMW 750iL (Islandgrun-metallic 273 ) ( euro )
    '91 BMW 735i ( Mauritius Blau 287) ( euro )
    '89 BMW 735i ( Delphin Metallic 184 ) ( euro ) & LPG
    '89 BMW 730i ( Islandgrun-metallic 273 ) ( euro )
    '05 Peugeot 407 SW (Dolomites)

  3. #3
    PatrickC88750
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    Yes | No

    Try "the other board"

    Mihai, I read your earlier post but don't know what else could have affected the DME to inject more fuel than what the fuel schedule says. I assume what is happening now is that your M30 is burning rich. But not so rich that you can smell raw fuel. Think air, spark, fuel pressure, and temperature. You swapped AFM, so air is out; Runs smooth, so plugs good and cables correct order; fuel pressure LPG and gasoline assume not both failed at the same time; temperature sensor replaced.

    Could it be wiring from temperature sensor to DME, or from AFM to DME? Unplug each injector one by one to perform a drop-rpm test, and see maybe one or two cylinders are not contributing to combustion. Unlikely because you said engine runs smooth but no loss trying. If you are tired of hunting, hook the DME up to a more elaborate BMW code reader that can show the coolant temperature to see if that is always interpreted to be cold.

    Lastly, try asking on b i m m e r b o a r d d o t c o m slash E 3 2 to see if (many) other E32 owners have come across the same thing.

  4. #4
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    Re: Try the other board

    Thank you for reply Patrick.
    I am now at the third DME and I have some results. I took the car on a short 200 km trip and the fuel consumption dropped finally to 11,8 l/100km, and this on LPG so on gasoline is slightly less ( with my other 735, same road conditions and distance the fuel consumption is 9,2 l/100km gasoline). However, when using this DME, idling is a little rough. Unplugging injectors did not revealed something new. Since I do not have access to a more elaborate code reader right now , I will have to postpone the temperature reading test. Digging forums is what I do best :) and I usually use posting messages as a last resort after a long search session.
    Mihai G.

    '91 BMW 850iA (Mauritius Blau 287)

    '91 BMW 750iL (Islandgrun-metallic 273 ) ( euro )
    '91 BMW 735i ( Mauritius Blau 287) ( euro )
    '89 BMW 735i ( Delphin Metallic 184 ) ( euro ) & LPG
    '89 BMW 730i ( Islandgrun-metallic 273 ) ( euro )
    '05 Peugeot 407 SW (Dolomites)

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