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M20 Cutting out/jerking

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    M20 Cutting out/jerking

    Ok so I have an 1988 325i Europe spec and about 10 days ago my car started cutting out/jerkin mid drive. The problem i have only occurs when car is warm. So about 10-15 min after driving.

    The first few days the jerking was violent and I barely could drive. After that I ordered rotor, distributor, new spark plugs, spark plug cables and coil and the violent jerking was gone. Now the car has the problem where when it gets warm it starts cutting out randomly, with no pattern or consistency. When this happens it can happen while I give gas or when I’m standing still or just coasting. In the gauge cluster the rpm, mpg and temp gauge all stutter and cut out randomly as if the car has some electrical issue. But it’s only those three gauges, the other ones are fine. What I also experience is that when the car is cold the car will let me rev to redline but when the car gets warm and about 10-15 after driving it gives me a limp/safe mode where I can only rev to about 4.5k/5k rpm. What I also noticed in the engine bay, the little space where the cps sensor threads between beside the timing cover, the plastic protection cover is missing.

    The only things I haven’t replaced are fuel filter, o2 sensor, crank position sensor and maybe other things if you guys have any recommendations. What could cause a limp mode?

    #2
    There are 3 relays in the Engine bay underneath a black plastic cover. From left to right they are Main Relay, Fuel Pump Relay, and O2 Relay. Sometimes the Fuel Pump Relay and O2 relay are swapped in position.

    Pull the plastic cover and each of the relays one by one. Inspect for corrosion on each of the contact terminals. Light sand and bend the terminals out slightly and reseat. Adding dielectric grease to the terminals might not be a bad idea either.

    Check the main engine ground strap from the oil pan to the side of the chassis and also the hood strap ground.

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      #3
      Originally posted by e30vert View Post
      There are 3 relays in the Engine bay underneath a black plastic cover. From left to right they are Main Relay, Fuel Pump Relay, and O2 Relay. Sometimes the Fuel Pump Relay and O2 relay are swapped in position.

      Pull the plastic cover and each of the relays one by one. Inspect for corrosion on each of the contact terminals. Light sand and bend the terminals out slightly and reseat. Adding dielectric grease to the terminals might not be a bad idea either.

      Check the main engine ground strap from the oil pan to the side of the chassis and also the hood strap ground.
      thank you, will check

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        #4
        Also check that the CPS sensor is mounted firmly and has not loosened up. Swapping temporarily with a new or known good CPS might be another course of action. Just wire it over the top of the engine temporarily instead of having to route it through the plastic channel behind the pulley. Or if you have a multimeter measure the resistance of the outer pin on each side of the 3 pin connector for the CPS . From outer pins to center pin it should read approx 20 Ohms and from outer pin to outer pin on the 3 pin connector it should read approx 40 Ohms

        Only take one action at a time and then test the running of the vehicle so you know what actually solves the issue.

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