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Stock M20 runs like a tractor

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    Stock M20 runs like a tractor

    OK next things next on the list of things to be done on my M20B20 With L Jetronic. Since I got the car it has been running roughly and making a slight tapping (pinging?) noise towards the rear of the engine. It runs loudly and sounds like a tractor. I've changed the timing belt and played with the ignition timing in addition to putting in brand new spark plugs and spark plug leads, changing the fuel filter and oil. I fixed one leak I found in the vacuum lines. I haven't gone to the point of doing a smoke test. Is there anything I'm missing? Here is a video. What does it sound like? https://youtu.be/W8TRDyZoAyc And when messing with the distributor timing https://youtu.be/I7gQc_Dk_CM

    #2
    Vacuum leaks are probably the single biggest headache with these engines. Besides the obvious hoses, the intake boot is always suspect. Adjusting the valves would probably take most of that noise out.
    2004 525i Manual - 1985 325E Coupe Manual

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      #3
      Pinging on the distributor m20's is more than likely too much timing from a faulty distributor advance (which is vacuum and centrifugal advance). Add that to the higher compression and lack-luster fuel and they are quite unhappy.
      john@m20guru.com
      Links:
      Transaction feedback: Here, here and here. Thanks :D

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        #4
        I forgot to mention that I put a brand new timing belt and new intake boot on the car recently. No change

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          #5
          Originally posted by ForcedFirebird View Post
          Pinging on the distributor m20's is more than likely too much timing from a faulty distributor advance (which is vacuum and centrifugal advance). Add that to the higher compression and lack-luster fuel and they are quite unhappy.
          So you recommend trying high octane fuel or adjusting timing some more? I'm not sure about how to adjust the vacuum advance.

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            #6
            You don't have a location, so unsure if you are in the US. Fuel ratings are different from EU to US, so yes, 89 octane or better (91+ preferred). There is no "adjustment" for vac advance, there's mechanical vac canisters, check valves etc. Then there's also a weight inside the distributor that advances timing as RPM goes up. If either system is faulty, the timing will be all over the place.
            john@m20guru.com
            Links:
            Transaction feedback: Here, here and here. Thanks :D

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              #7
              Originally posted by ForcedFirebird View Post
              You don't have a location, so unsure if you are in the US. Fuel ratings are different from EU to US, so yes, 89 octane or better (91+ preferred). There is no "adjustment" for vac advance, there's mechanical vac canisters, check valves etc. Then there's also a weight inside the distributor that advances timing as RPM goes up. If either system is faulty, the timing will be all over the place.
              I'm in Australia which I believe uses the same as a Euro spec. I have an auto trans so there is only a vacuum advance line Sent from my Mars pro using Tapatalk

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                #8
                That is the RPM sensor. It's got and electrical plug on it. There should also be a vacuum canister and at least one vacuum line going to it (about 3mm).
                john@m20guru.com
                Links:
                Transaction feedback: Here, here and here. Thanks :D

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                  #9
                  If it looks like a tractor, it's probably a tractor.



                  In all seriousness, a smoke test is your best bet to accurately highlight any vacuum leaks.
                  Yes it's a bit of messing about (and may require a DIY smoke tester if you don't have one) but it takes the guess work out.

                  From the video, does sound like the valve clearances need a check.
                  My M20 has 197k km on it and even with correctly adjusted valves it sounds a bit like a sewing machine.

                  As you're also in AUS, I'd stick to 95 RON fuel.
                  Our old leaded super petrol was 94-96 RON.

                  You can cheap-out with E10 which is circa 95 RON - but keep in mind the energy density of E10 is lower than regular fuel.

                  E30 320i vert
                  But daily drive is Volvo V60 Polestar

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                    #10
                    Every M20 I’ve listened to sounds like a tractor. I really like the sound, it gives the engine character.

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