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  • Bogging

    For the first time last week, the car would not start. Had to crank it about eight times before she turned over. Ran fine until I took an on-ramp in third gear at around 4500 RPMs, Just after coming out of the apex I accelerated and the car bogged for a few seconds, then accelerated. Today when I took it out, started fine however bogged again on another on-ramp coming out of the apex hard. 1/2 tank of fresh gas in the car. Plugs, wires, cap, rotor all relatively new.

    Thoughts? I’m starting to wonder about the 33 year-old fuel pumps. Any chance the in-tank pick-up pump starts to starve the car during acceleration in corners before they die?

  • #2
    Based on your description, that would be my first thing to check if its still stock, in tank fuel pump, then external (while im in there fuel filter) then if all that checks out my next things to check in order would be:
    Fuel pressure regulator
    Injectors / O2 sensor (I'm tied there)

    FWIW, when I got to a similar running issue with my street car, I replaced the in tank pump and then all of the above (except external pump and my car has A/n so no AFM).
    Basically at the same time I did the ~30 year old in tank pump I did a fuel filter, FPR, new injectors and O2 sensor.
    It ran like a different car. I had no idea that incrementally I was going down on performance over time.
    Last edited by jimmy p.; 08-01-2020, 05:42 PM.
    jimmy p.
    87 E30 M3 Prodrive British Touring Car
    88 E30 M3 Zinnoberot - Street
    88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
    92 E30 M Technic Cabrio - S14 POWERED!
    98 318Ti M44, Base - Morea Green
    04 Ford F350 - V10


    • #3
      I couldn't agree with Jimmy more. My $$$ is on the in tank pump though. It's a low pressure pump that feeds the main high pressure pump. If the high pressure pump isn't getting enough fuel fed to it, then you will basically run out of fuel (bog).

      Ron ///Man

      • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
      • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
      • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
      • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
      • '89 M3 M3T / ITR Club Racer
      • '94 Spec E36 - Eh....
      • '09 M3 - Tarmac Terrorist
      • '04 330Xi Sport 6 Speed - Snowmobile
      • '07 530 Xi - Highway Star


      • #4
        Thanks guys. I’ll get an BMW in-tank and a filter. Already have a new external Bosch pump on the parts shelf. I’ll also do the tank hoses while I am in there. Hopefully no surprises when I open the tank.


        • #5
          classic fuel pump symptoms. easy to check, you can hear the pumps humming with an auto stethoscope. if you can hear them loudly with just your ear, they are failing. if you can't hear them, they are dead....

          and good call on replacing the hoses, including the ones in the engine compt. if they are original, they are LONG past overdue.
          75 M2
          88 M3


          • #6
            Like everyone said, most likely fuel pump(s).... however don't be surprised if it isn't... a couple of years ago I had a stumbling issue only on hard right turns, in any gear. It turned out to be corrosion and intermittent contact in the AFM connector pigtail. As these cars are now basically 30+ years old, they get more creative in challenging you...