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06/1988 324td touring - will not rev up

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    06/1988 324td touring - will not rev up

    Let me preface this, with me fully admitting that I know 0% about anything regarding the diesel engines...

    Customer dropped off this 6/88 324td touring (German import) with a serious drivability issue. It does not rev up at all. Period. It has a fast idle upon start up (1500-2000 or so, does not surge, and this could be a separate issue entirely) but upon depressing the throttle pedal, any amount, the idle comes back down to 1000.

    This is a later style diesel engine, with no throttle body, no throttle cable, etc... it only has a potentiometer under the dash - that is it. There is very little about the 324td on the internet, especially these later style engines, with no throttle cable.

    Customer has installed a new OE fuel filter, and a later style potentiometer, from an E46 diesel (the part interchanges, apparently), to which, the problem still remained.

    Any advice, from someone who knows the diesel engines, would be greatly appreciated. Just would like to know what direction I should start looking at, before I go down the rabbit hole...

    Many thanks.

    *** 5 November 2019 update - learned a lot about diesels and M21s in the last couple weeks. determined the engine's mechanical fuel injection pump needed rebuilt. ***

    Last edited by e30austin; 11-05-2019, 12:52 PM.
    '72 2002 pickup | '88 M5 | '89 330is | '89 M3 | '01 Z3M | '11 328xi-t


    #2
    If I recall, the 324td effectively has two management computers, one for idle and the other to actually run the car, and it can run with one or both non-functional, or at least mine could. Additionally, there are vacuum and reference sensors that compensate for altitude and probably other things. When I was diagnosing an issue I basically verified fuel and started unplugging stuff until it ran decently, and traced the issue that way. Parts availability sucks, so I hope it's something you can actually get today.

    Best reference: http://www.mye28.com/viewtopic.php?t=88207
    Functional manual: https://www.bmwtechinfo.com/repair/main/137en/

    GLW the diag, and hope you get the customer back to rolling coal ASAP.

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      #3
      Hey, thanks for the info! I've been messing about with it for a little while this morning. I effectively unplugged every single sensor on the engine, to no avail. Unplugging the idle controller made no difference. The only thing that I will note, is once the potentiometer is unplugged, the idle returns back to normal (1000 rpm). Nothing else made a difference. Wishing there was a wiring diagram for the late engines around... :/
      '72 2002 pickup | '88 M5 | '89 330is | '89 M3 | '01 Z3M | '11 328xi-t

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