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M20 engine vibration and rough running at 1800 rpms and above

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    M20 engine vibration and rough running at 1800 rpms and above

    I just picked up my e30 from a reputable shop at closing time. I drove off and right away i notice the engine doesn't nt sound right starting at 1800 rpms with vibration that increases with the rpms.and doesn't go away. A few blocks later i am able to put it neutral and rev it up slowly and it does the same thing while in neutral and no load. The Shop is closed, they are gone and I will return tomorow but I would like to gain some knowledge here from the experts on this forum. The sound and vibration are similar to an engine not firing on all cylinders. the shop has had this car for several months. I like the shop and the people at the shop but somethings not right.

    The details

    I dropped off my 90 325i with bad rings according to the PO. along with a supposed to be good 88k mile M20b25 motor pulled by a different shop for an m50 upgrade. I wanted the good motor freshened up with new hoses, drive belts, compete gasket replacement, water pump, belts, crankshaft seal, motor mounts, oil level sender, thermostat, ignition wires. it was decided to rebuild the head with HD rockers, 274 cam, new head bolts, rocker shaft plug, camshaft seals and gasket. Additionally they thought I should replace the rod and main bearings so we did.

    Any common traits with this since it sounds and feels rough in gear under load and with no load.


    #2
    someone leave a spark plug lead off?

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      #3
      tomorrow I am having the e30 towed back to the shop. all hoses, belts and gaskets are new and on. the shop thinks it could be the chip from Squid but They handed me the keys at closing time and it did not run smoothly at all. So it was not running properly for them is my conclusion. its either vacuum, fuel and spark or compression. I suspect compression. I will be sure to keep this going as they say they will fix it.

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        #4
        Crank position sensor?

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          #5
          Interested in the outcome. Following.
          "If everything seems under control, you're just not going fast enough"
          -Mario Andretti.

          ___________________
          River City Bimmers BMW CCA
          2005 X3 3.0i ZPP, Htd seats, Htd strng, Black Sapphire on Terracotta.
          2002 ///M3 Coupe, Steel Gray Metallic on black leather, HK, three pedals.
          1991 E30 325ic, AW, Black Leather, Black top, Three Pedals.

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            #6
            Before It was loaded on the tow truck I had a bit more time to run it without any distractions. I warmed it up then in neutral, I slowly revved it and at 2,200 RPM's the sound and vibration are noticeable. The sound is a slight miss in the rhythm an engine makes. No popping, no backfiring, just vibration and the sound increasing as the RPM's increase. I fear that its internal since the block, crank, rods, pistons, rings were not changed as their inspection deemed that not necessary. The head was rebuilt, 274 bimmerheads cam, squid chip, main and rod bearings were the only internal parts changed. I am hopeful my next conversation with them is on the details of what's wrong before any attempt to fix is made. I have stated that I want to know what is going on. I do not want a come get your car we fixed it already. That would make me suspicious as to what I am getting from them.

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              #7
              Update: The Shop thinks its the poly engine mounts. I do not have any experience with this car. Bought it with bad rings, took it to them and my first real drive was the other day when they said its ready. I do how ever have experience with solid engine mounts as my 914-6 race car had solid aluminum trans mounts and poly engine mounts those mounts connected to the metal bulkhead mount that I welded to the chassis. That car with a 220 HP, 2.5 ltr, big cam, 10.5 - 1 compression did not vibrate as the RPM's increased. Sure the I could feel the car twist under load but the harmonics did not change. I see this is not an interesting thread for many, especially the experienced crowd but any experienced advice would be welcome.

              Comment


                #8
                I don't think that people aren't interested, it just seems one of those things that's hard to diagnose without seeing it.
                You could try posting a video or taking the car to another shop for a second opinion.
                There's a trouble shooting thread by jlevie that you could follow posting results as you work through it.
                Motor mounts are easy to replace so you could try replacing them to see if it helps.
                Same with the chip.
                Did the shop measure the P to V clearance when installing the new cam?

                Comment


                  #9
                  Its not going to be the mounts, 6clr engine running properly is perfectly smooth and would free rev smooth on bricks. If you are getting as bad of roughness as you describe when you are free revving then its something fundamentally wrong. If nothing jumps out i would have the shop do a compression test, then you can at least get some confidence that the mechanical job was done well. Then start looking at the injectors or the ignition system and try and pinpoint which cylinder is not firing properly. If the injectors haven't been cleaned and flow tested as part of the overhaul they really should have been.

                  Did they adjust the valves properly?




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