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Thread: Secondary Air System Vacuum Failure - M44

  1. #1
    Join Date
    Apr 2015
    Location
    Los Angeles
    Posts
    1
    My Cars
    1998 BMW 318ti

    Secondary Air System Vacuum Failure - M44

    I have no vacuum in the secondary air system. All components downstream from the canister are working fine. The furthest I've trace the vacuum line back to its source is the container (which is under the lower intake manifold and very difficult to access.) In a diagram of the secondary air system vacuum system, a check valve is the next component upstream from the container, then a "T" splitter, and then another 470 mm of 3.3 mm vacuum line that goes to the vacuum source, which I assume from my research is somewhere on the intake manifold. There are lots of threads explaining how to replace the rivets with bolts and nuts on the secondary air pump, to make sure your stop/cut-off valve between the secondary air pump and the exhaust manifold is working, and to make sure the vacuum control that supplies vacuum to the stop/cut-off valve is working. But there's nothing about what to do if there's no vacuum coming out of the canister. Anyone who explaines the vacuum system upstream from the canister would be making history. Because this information exists absolutely nowhere, not in the Bentley manual, not in any forum, not in the factory manuals, nowhere. First, could someone please tell me where the vacuum source for the secondary air system is? I would like to identify the vacuum source before tearing everything apart just to make sure it's not clogged. Could someone give me a description of how to access the secondary air vacuum system upstream from the vacuum control switch? Photos or hand drawn diagrams would be deeply appreciated.

  2. #2
    Join Date
    Aug 2017
    Location
    San Francisco
    Posts
    19
    My Cars
    1998 Z3 1.9
    Hi, I know this is really old, but I have the exact same problem in my 1998 Z3 and was hoping you might found a fix in the end?

  3. #3
    Join Date
    Aug 2017
    Location
    San Francisco
    Posts
    19
    My Cars
    1998 Z3 1.9
    I got to the bottom of it and want to share my findings to help anyone out with this problem:

    The vacuum lines crack over time. While it is relatively simple to get to up until you reach the canister, it becomes impossible to access from there. I had to take apart the upper intake manifold to access the vacuum line behind the canister. Just a short line to the T-Splitter, but it was totally cracked as well. Luckily, the T-Splitter still provided a vacuum for me, so I did not have to take it any further.

    If you do, then be advised that from the T-Splitter one line goes to the engine (I don't know where exactly) and one goes underneath the car, I believe somewhere to the fuel supply or gearbox. The second line is easy to trace from underneath the car (provided it is still factory coloured black with a white stripe). The other one that goes to the engine, is still a mystery to me and I don't know where exactly it enters the vacuum source.

  4. #4
    Join Date
    Aug 2017
    Location
    San Francisco
    Posts
    19
    My Cars
    1998 Z3 1.9
    Please check this thread on the issue, with a diagram and a "solution": https://www.bimmerforums.com/forum/s...manifold-)-1-9

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