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    hesitation worse when A/C on

    I'm trying to solve a hesitation problem on my Touring. Threads here on r3v have been helpful, but I haven't found the problem yet.

    I noticed yesterday that the hesitation is worse with the A/C on, and wondered if that might help narrow down the potential causes.

    Without A/C
    Hesitation at WOT, at med to high revs (tach is non op, so don't know exact rpm). Seems to be getting worse over time.

    With A/C
    Hesitation much worse, at partial throttle and lower revs.

    Parts replaced the day I bought the car
    spark plugs
    cap and rotor
    air filter
    fuel filter

    First noticed the hesitation 5-600 miles after the tune up.

    Parts replaced Friday that did not fix the hesitation
    plug wires
    coil

    Any thoughts on the cause of the hesitation?

    Cory
    1992 325i Cabrio
    1988 320i Touring
    2000 M5
    1977 530i
    2015 328i - Euro Delivery/Performance Center Delivery
    BMWCCA
    E30CCA

    #2
    If your foot is to the floor I'd suspect TPS. The only thing I can think of that the ac would effect is idle which is also related to the tps.

    Other than that perhaps a flat spot in the AFM, vacuum leak, fpr or a bad injector.

    Let me know if you don't have spares to swap in as I probably do
    Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

    https://www.r3vlimited.com/board/sho...86#post4944786
    Alice the Time Capsule
    http://www.r3vlimited.com/board/showthread.php?t=360504
    87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

    Comment


      #3
      Thanks Jeff! I'll text you when I'm ready to dig in again.

      Cory
      1992 325i Cabrio
      1988 320i Touring
      2000 M5
      1977 530i
      2015 328i - Euro Delivery/Performance Center Delivery
      BMWCCA
      E30CCA

      Comment


        #4


        Go through my thread here. I experienced the same issue.
        AWD > RWD

        Comment


          #5
          Originally posted by Kershaw View Post
          http://www.r3vlimited.com/board/showthread.php?t=372569

          Go through my thread here. I experienced the same issue.
          Thanks Kershaw. Lots of good info in your thread, but my hesitation is a little different: not only at WOT and no CEL light.

          From the thread, it looks like your problem was fixed by the megasquirt, but it seems like you never figured out what was actually causing the problem.

          One post caught my attention - if it's fuel related, that would not trigger the CEL.
          1992 325i Cabrio
          1988 320i Touring
          2000 M5
          1977 530i
          2015 328i - Euro Delivery/Performance Center Delivery
          BMWCCA
          E30CCA

          Comment


            #6
            When my hesitation was undrivable, what fixed that was replacing the toothed harmonic balancer. But since that was 1.5 years ago now I can't remember if I was getting CELs with it. But it was at all RPMs and all over the place.

            But yeah, I would go through the standard list and start checking and replacing. JLevie experienced an identical issue, he fixed it with a new engine harness after going through 3 used harnesses that were good in other cars. After checking with 3 other engine harnesses, I decided to go that route as well, but they are NLA. So I went to megasquirt. It was a great upgrade.
            AWD > RWD

            Comment


              #7
              Originally posted by Kershaw View Post
              When my hesitation was undrivable, what fixed that was replacing the toothed harmonic balancer. But since that was 1.5 years ago now I can't remember if I was getting CELs with it. But it was at all RPMs and all over the place.

              But yeah, I would go through the standard list and start checking and replacing. JLevie experienced an identical issue, he fixed it with a new engine harness after going through 3 used harnesses that were good in other cars. After checking with 3 other engine harnesses, I decided to go that route as well, but they are NLA. So I went to megasquirt. It was a great upgrade.
              Great info. Thank you!
              1992 325i Cabrio
              1988 320i Touring
              2000 M5
              1977 530i
              2015 328i - Euro Delivery/Performance Center Delivery
              BMWCCA
              E30CCA

              Comment


                #8
                Update: Replaced the O2 sensor and spark plugs last weekend and.......hesitation gone!

                Don't know the age of the O2 sensor, so it could have been original (179k miles/28 years). The spark plugs had less than 2k miles on them and looked a lot worse than I anticipated.
                1992 325i Cabrio
                1988 320i Touring
                2000 M5
                1977 530i
                2015 328i - Euro Delivery/Performance Center Delivery
                BMWCCA
                E30CCA

                Comment


                  #9
                  Originally posted by cory58 View Post
                  Update: Replaced the O2 sensor and spark plugs last weekend and.......hesitation gone!

                  Don't know the age of the O2 sensor, so it could have been original (179k miles/28 years). The spark plugs had less than 2k miles on them and looked a lot worse than I anticipated.
                  I can see how a bad o2 sensor could easily cause your plugs to foul. Glad you got it resolved.
                  Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

                  https://www.r3vlimited.com/board/sho...86#post4944786
                  Alice the Time Capsule
                  http://www.r3vlimited.com/board/showthread.php?t=360504
                  87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                  Comment


                    #10
                    I'm having the same problem with the a/c on my M42. Car idles fine without a/c on. Switch a/c on and car stumbles, idle drops to 500?600. Recently purchased car with no a/c. PO had broken high side line port. I added new dryer, belt, high side line, vacumn system, recharge.

                    Highway driving a/c is freezing. Stop and go traffic, car stumbles at every stop. Close to cut off.

                    I have changed all hoses under intake. ICV has been cleaned thoroughly. No leaks. New intake gasket. Gotta have a/c in Fla this time of year. Any answers...????

                    Comment


                      #11
                      Problem Not Fixed!

                      Update: So after approx. 1,200 miles, the hesitation came back. Something is still destroying the spark plugs, and now I see the pattern. I replaced the plugs again, and the car runs great. New plugs last about 800 - 1200 miles before the hesitation begins. The only additional changes since last time are a refurb AFM (from Bav Resorations) and cleaned ICV.

                      Here are pics of the plugs that were in the car for approx. 1200 miles, in order from 1-6. Before I start throwing money at new parts, I'm hoping to get some opinions on what might be causing the plugs to get destroyed so quickly. Any thoughts would be greatly appreciated.













                      Thanks, Cory
                      1992 325i Cabrio
                      1988 320i Touring
                      2000 M5
                      1977 530i
                      2015 328i - Euro Delivery/Performance Center Delivery
                      BMWCCA
                      E30CCA

                      Comment


                        #12
                        Burnt Valves or possibly valve adjusted too tight letting valves hang open and cooking your plugs.

                        Worth a look, I don't think this throws a CEL. Others may correct me if I am wrong.

                        Comment


                          #13
                          If you haven't freshened the injectors (and o rings)I still have the ones I pulled from my cabrio that were working fine. May be worth trying
                          Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

                          https://www.r3vlimited.com/board/sho...86#post4944786
                          Alice the Time Capsule
                          http://www.r3vlimited.com/board/showthread.php?t=360504
                          87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                          Comment


                            #14
                            Thanks Jeff! I will text you.

                            fastbub - Thanks for the suggestion. I have no experience with burnt valves. If that's the problem, would the car run as if nothing's wrong with new plugs? Any other symptoms of burnt valves?

                            Thanks, Cory
                            1992 325i Cabrio
                            1988 320i Touring
                            2000 M5
                            1977 530i
                            2015 328i - Euro Delivery/Performance Center Delivery
                            BMWCCA
                            E30CCA

                            Comment


                              #15
                              If you're burning valves, you'd have hard starting, rough idle, and a myriad of other issues beyond a WOT stumble. That said, checking the valves is easy and if it hasn't been done, you should check them.

                              You may want to rent a fuel pressure tester and make sure you're maintaining pressure at WOT, just to check that one off the list. Also might be worth looking at the cap and rotor to see what kind of shape they are in.

                              Project M42 Turbo

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