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Engine Runs Better After Being Redlined

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    #1

    Engine Runs Better After Being Redlined

    I have an 89 325i with an M20B25 and when I first start it and drive, it doesn't seem to pull as hard as it should. It also tends to shake a lot under load at lower rpms (1500-2500). A few days ago, once the engine warmed up, I gave it WOT and brought it up to redline in first, and after that, it was like the engine clicked on. It pulled noticeably harder and the shaking in 3rd and 4th completely went away.
    I've tried this every time I've driven since and every time I've seen the same results. I just bring it to about 6500 once or twice and it wakes the engine up for the rest of the drive.

    What could cause this? I'm thinking possibly clogged injectors and then as they get more pressure they kind of free themselves? I'm honestly completely lost.

    Sent from my SPH-L720T using Tapatalk
    1988 325is - Totaled, Hit and Run
    1994 530iT - Rusty, Not Running, Gone
    1989 325i - Clean Body, Barely Runs
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    #2
    The culprit could be the aluminum elbows connecting to the throttle body. They can be quite loose and create vacuum leaks. As you rev up the engine, it creates enough vacuum to temporarily pull the elbows tight. I would do a smoke test at 2-5 psi and wiggle the elbows at the same time to see if smoke is coming out. Or just JB weld the elbows and call it a day.

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      #3
      The good old- fashioned Italian tune- up...

      I too would go looking for air leaks, and confirm that your tps isn't loose!
      If it's flopping around, then an excursion to WOT would move it.

      Also look for something that would cause the ECU to go to a default map-
      loose wires to sensors, etc... old EFI cars are sometimes a handful to troubleshoot...

      t
      now, sometimes I just mess with people. It's more entertaining that way. george graves

      Comment

        #4
        I'll check on those elbows and maybe try a smoke test. I have a feeling this could be a small leak. The idle is also a little strange

        Sent from my SPH-L720T using Tapatalk
        1988 325is - Totaled, Hit and Run
        1994 530iT - Rusty, Not Running, Gone
        1989 325i - Clean Body, Barely Runs

        Comment

          #5
          Originally posted by Yeltsew7 View Post
          I'll check on those elbows and maybe try a smoke test. I have a feeling this could be a small leak. The idle is also a little strange

          Sent from my SPH-L720T using Tapatalk


          Like others have said, check the elbows--if they are loose, JB weld then.

          Also check the injector harness connector under the intake manifold for corrosion/damage. It may be moving around under WOT.


          Sent from my iPhone using Tapatalk

          Comment

            #6
            Maybe you blew the cobwebs off your spark plugs. How do they look and do you know the history of them?

            Comment

              #7
              Originally posted by e30davie View Post
              Maybe you blew the cobwebs off your spark plugs. How do they look and do you know the history of them?
              They're brand new

              Sent from my SPH-L720T using Tapatalk
              1988 325is - Totaled, Hit and Run
              1994 530iT - Rusty, Not Running, Gone
              1989 325i - Clean Body, Barely Runs

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