Rod knock? *video*

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  • ParsedOut
    E30 Fanatic
    • Sep 2005
    • 1437
    #1

    Rod knock? *video*

    I've noticed my M20B25 has started to exhibit a "rod knock like" sound at idle. Along with that is a new intermittent buzz. The knock sound is audible at 10 seconds and 39 seconds, although it's pretty much constant in person, it's hard to hear over all the valve/injector noise in the video. It almost sounds like it's about to run out of gas, you know that sound an engine makes when it's about to stall out?

    Performance is still very good, car has linear power delivery, no strange noises during acceleration. I did a compression test a few months ago (about 20 miles driven since) and the numbers were 165 across all cylinders with 4 cranks. Engine feels healthy other than this new disconcerting sound at idle.

    In a possibly related issue, I have noticed my fuel pump is loud as hell and the injectors look like they've never been touched. Could this just be a symptom of poor fuel delivery?

    https://www.youtube.com/watch?v=OHlIJjv6Nsw
    Tags: None
    • jlevie
      R3V OG
      • Nov 2006
      • 13530
      #2
      Sounds just don't come through with enough clarity is a video to attempt a diagnosis. Take the car to a BWM shop and have them diagnose the sound.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

        Comment

        • tim88325is
          Wrencher
          • Jul 2008
          • 201
          #3
          Does the knock go away when you push the clutch in? If so, just a input bearing issue, not serious...

            Comment

            • ParsedOut
              E30 Fanatic
              • Sep 2005
              • 1437
              #4
              The sound doesn't change if the clutch is in or out. I'm pretty sure it's fuel related now, sounds like the engine is trying to stall out. I know my transfer pump is out and the main pump is working hard and the injectors appear to be original so I'm going to start there.

                Comment

                • jlevie
                  R3V OG
                  • Nov 2006
                  • 13530
                  #5
                  Before you spend any money on parts (other than the transfer pump), Have a BMW shop diagnose the car.
                  The car makes it possible, but the driver makes it happen.
                  Jim Levie, Huntsville, AL

                    Comment

                    • Paradox
                      Grease Monkey
                      • Jul 2010
                      • 337
                      #6
                      sounds like valves needing adjustment to me....when was the last time you did that? Most of the fuel pumps that are original to these cars will be on their way out by now. Maybe all you need to do is a little maintenance and she will be fine again

                        Comment

                        • ParsedOut
                          E30 Fanatic
                          • Sep 2005
                          • 1437
                          #7
                          I've adjusted the valves twice in the last 2 months, they aren't holding spec because the eccentrics are flat spotted. New ones are on order. I'm not replacing the injectors, just cleaning them, new filters and o-rings. The entire ignition system has been replaced along with the timing belt. The compression is good, so the only thing left is fuel system or possibly AFM/vacuum issue.

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