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4068RE: [bmw e28] Power problems with 1985 (C Reg) 520i

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  • george mogos
    Dec 17, 2005
      Hi there

      By the sound of it - refusing to accelerate past a certain engine speed and stuttering under acceleration - it makes me think of the ignition timing setting. Ignition timing is not fixed for the whole engine speed range, it is regulated by a centrifugal actuator in the distributor and by a pressure gauge in the intake - that is to monitor both the engine speed and the throttle position. The higher the engine speed the more ignition timing will be "forwarded" in order to make the most of the explosion pressure at TDC. If the ignition timing is well ahead of the prescribed 20-ish degrees (check your Bentley or Haynes manual for your engine) and adding to that the dynamic advance that the engine itself generates, there will be a certain threshold at which the ignition will happen well ahead TDC, so gigantic forces will actually "brake" the piston - and consequantly the whole engine. If the engine has a mechanical distributor, just "back it off", by loosening the screw underneath it
      with the engine idling and turning it gently in the clockwise direction (mark the position of the distributor before this in case you want to retrieve it later). The engine speed should decrease when you do this. I can't recommend how much you should turn it, but if you do it in steps of a few degrees each you will get to test the effects by driving the car after each adjustment. Of course, you MUST tighten the screw after you adjust the timing, otherwise frictional forces will drive the distributor astray. If this DIY method will make you laugh (and I have to say it takes years of experience to actually do it properly just by listening to the engine), any garage will do it for you for a small fee by using a special flash tool. I hope this helps you out, but if I wasted your time I hope I may be pardoned.
      Cheers, George

      dave ruiz <daveruiz50@...> wrote:
      Have you done a fuel pressure test? -Dave Ruiz



      If you plant poison ivy, you won't harvest strawberries. - William Stephens
      When I die, I want to die like my grandfather-- who died peacefully in
      his sleep.
      Not screaming like all the passengers in his car."
      --Author Unknown





      >From: "graham_e28"
      >Reply-To: bmwe28@...
      >To: bmwe28@...
      >Subject: [bmw e28] Power problems with 1985 (C Reg) 520i
      >Date: Wed, 14 Dec 2005 22:12:38 -0000
      >
      >Hi, I'm hoping some of you may have some suggestions. My 1985 (C reg)
      >520i will no longer go above 2500 rpm in any gear or when revved
      >stationary - above this it 'stutters' and all loses power. I have had
      >a diagnostic done on the ECU but am told all is well. It has been
      >suggested that one of the sensors has failed and the ECU has
      >automatically entered mid range figures for its output and gone into
      >'LOS' mode to prevent the engine from being damaged - however, I
      >cannot find anything about this in any of the manuals available to me.
      >The ECU is the early L-Jetronic and I'm also told that the number of
      >sensors is limited and anyway, the diagnostics do not extend to the
      >sensors as with later models.
      >
      >Any suggestions welcome from those more experienced with these
      >wonderful but frustrating beats,I posted before on 23 Nov 05 (message
      >4015) but no responses ( probably you're all as confused as I am )
      >.... it's getting awfully embarrassing only being able to do 65mph on
      >the motorway and having zilch acceleration. Even push-bikes beat me
      >away from traffic lights!
      >
      >Thanks in advance
      >Graham
      >
      >
      >
      >

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