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Thread: Testing maf readings on a 1999 750...any ideas?

  1. #1
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    Testing maf readings on a 1999 750...any ideas?

    Hi guys & Happy Thanksgiving

    I have been chasing down an intermittent P1270 code on an engine that I have been restoring. It runs well and I have replaced the majority of gaskets, lines, electronics including MAFs, injectors, OSV, and all the typical ignition parts. I would like to know of a way I can use my volt meter to read the output voltage back to the computer from both of the MAFs while the car is running. The harness is a 4 pin round connector and I rather not destroy trying to splice in a wires on each MAF sesnor. Does anyone know of a break out harness that can be used? I dont have factory scanner that would show both MAF readings...my cheap one only shows one reading for the MAF...and I believe its an average of both??

    Thanks again for your time and stay safe.

  2. #2
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    You can back-probe the connector - or - grind your meter probes to be needle-sharp - that's my usual plan!
    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. #3
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    Hi Tim,

    Thanks for the reply. I would have done as you suggested and back probed the connector...but these wires are encased and the entire round 4 pin plug is not exposed. I tried to see if the rubber on the harness could be peeled away but I dont see how.
    I guess I may have to make 2 extension harnesses that would connect to the sensor and the other end to the car harness?

  4. #4
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    1999 750il, 1995 325i, 1995 trans am, 1985 corvett
    Hi Timm,

    Would you know if the underhood ALDL connector would allow a scan tool to show 2 separate readings for the MAF sensors?? I believe using the OBD2 connector inside the cabin gives you the average of both readings. Any suggestions you may have would be deeply appreciated. Thanks for your time Rick

  5. #5
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    750IL/540iT/R53/E46Vert
    Who made the new MAF’s? Non OE have been a problem in the past. Any other symptoms?

  6. #6
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    Quote Originally Posted by 1999750il View Post
    Hi Timm,

    Would you know if the underhood ALDL connector would allow a scan tool to show 2 separate readings for the MAF sensors?? I believe using the OBD2 connector inside the cabin gives you the average of both readings. Any suggestions you may have would be deeply appreciated. Thanks for your time Rick
    They both allow selection of DME A or DME B - but you need the right diagnostics such as INPA
    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


    My BMW Repair YouTube Channel
    My Current 840ci Sport Individual
    My Current 650ci Sport Individual
    My E31 Repair and Information Website
    My E38 Repair and Information Website
    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

  7. #7
    Join Date
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    1999 750il, 1995 325i, 1995 trans am, 1985 corvett
    Hi CPHES,

    Thanks for the reply. I believe I replaced them with Bosch units. I dont believe there are any other symptoms...the car runs ok...I just get the check engine light sometimes with code P1270.

    I have been trying to track down the cause of it...and figured I could check the sensor voltages from both of the MAFs verify if they were reporting similar readings to the computer. The harnesses to both MAF sensors are completely encased and I didnt want to destroy the wiring. I was hoping I could find a scanner that would be able to read both MAF readings and display them separately. Would you have any suggestions?

  8. #8
    Join Date
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    1999 750il, 1995 325i, 1995 trans am, 1985 corvett
    Hi Tim...thanks again for the reply. I don't have INPA...but would like to find out where I could find the system to purchase. I have several scanners but these e38 are tricky and most scanners are not able to properly read them. I guess thats another reason to purchase INPA....any suggestions?
    Thanks again for your help

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