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    #1

    electrical problem...?

    So i finished my M30 swap earlier this week. Car has been fine. This morning I replaced my 02 sensor that had some exposed wire. I take it for a ride right after and everything is great. Hours later I leave my shop and car starts up fine. As i'm driving home I notice my radio keeps shutting off, and coming back on, then off and so on. I also notice the gauges dim a little then brighten up, and dim again.

    There was a major accident on the highway i was on, complete lockdown. Since i was low on fuel, i shut off the car. A few minutes later i had to move over for ambulances and cops to pass through and all of a sudden car doesn't start. Battery was drained. After about an hour, one of the cops jumped me. He had the cables reversed on my car, alot of spark going. then he put them on the right way and the car fired up immediately. So as i start driving now i have NO radio at all, and now my check engine light keeps coming on, goes off for a bit, then back on again etc...What could have happened that's causing the CEL to do this. Could this be because the jumper cables were reversed and F'd something up? Thanks guys
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    #2
    The initial symptoms sound like a bad alternator, which would cause a dead battery.

    Reversed polarity could have damaged any of the electronics in the car. Test the alternator and battery and repair as indicated. Then look at the other problems, if they are still present.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment

      #3
      Originally posted by jlevie View Post
      The initial symptoms sound like a bad alternator, which would cause a dead battery.

      Reversed polarity could have damaged any of the electronics in the car. Test the alternator and battery and repair as indicated. Then look at the other problems, if they are still present.
      Those were my first guesses as well, but today I put in a new alternator (140 amp), and threw in an optima yellow top as well. Drove home, and to an event i had at night fine. On my way home, my radio cuts out completely, i notice my gauges dimmed a bit, and my check engine light came on again. When i park in my driveway, i shut my lights off and the CEL goes away, turn lights on and CEL comes back on. I also notice the sound of the motor weaken with the lights on. What else could this be?

      All i can think of is when the coolant hose blew at one time i had the car on a slight uphill of a driveway and coolant had come into the car. At the drivers foot area on the side and bottom. Carpet had coolant stains on it. Is there a harness or any module down there that's shorting out because of the coolant that got on it?

      Thanks

      Comment

        #4
        There is nothing low down in the passenger compartment that could cause this.

        I hate to say it, but it sounds like your new alternator isn't working.

        Does the alternator/battery warning light in the cluster illuminate when the ignition is switched on? That bulb is the source of exciter power for the alternator and if not working the alternator won't properly.

        The system voltage when the engine is idling and the battery is fully charged should ~13.5v. When at 2500rpm it should be ~14v. And the system voltage should not appreciably drop when you load the system by turning on the headlights and/or HAVC blower.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

        Comment

          #5
          Originally posted by jlevie View Post
          There is nothing low down in the passenger compartment that could cause this.

          I hate to say it, but it sounds like your new alternator isn't working.

          Does the alternator/battery warning light in the cluster illuminate when the ignition is switched on? That bulb is the source of exciter power for the alternator and if not working the alternator won't properly.

          The system voltage when the engine is idling and the battery is fully charged should ~13.5v. When at 2500rpm it should be ~14v. And the system voltage should not appreciably drop when you load the system by turning on the headlights and/or HAVC blower.
          The battery light does not come on. The car started this morning. But on my way to work, same things happen again.
          Last edited by LuCifer; 03-01-2012, 09:34 AM.

          Comment

            #6
            jlevie means does the battery light illuminate with all the other warning lights when you turn the key to ON but not start the engine?

            Comment

              #7
              Originally posted by vpilarrt View Post
              jlevie means does the battery light illuminate with all the other warning lights when you turn the key to ON but not start the engine?
              Yes the battery light comes on with all the others.

              Comment

                #8
                So yesterday I pulled out the alternator, Today i had it checked at two different locations. The alternator is good. But its only putting out 11.2 V.
                Last edited by LuCifer; 03-06-2012, 12:30 PM.

                Comment

                  #9
                  Originally posted by LuCifer View Post
                  So yesterday I pulled out the alternator, Today i had it checked at two different locations. The alternator is good. But its only putting out 11.2 V.
                  Doesn't that signify it not being good? Anyways, how's your voltage regulator? Mine was charging low and the regulator cleared that right up.
                  - Josh
                  1990 325is

                  Need a shift boot?
                  Looking to buy shift boot frames, PM if you have one to sell

                  Here's what happens when you let the internet pick your license plate

                  Comment

                    #10
                    Originally posted by LuCifer View Post
                    So yesterday I pulled out the alternator, Today i had it checked at two different locations. The alternator is good. But its only putting out 11.2 V.
                    With the engine idling, what is the voltage on the exciter stud and what is the voltage on the output stud. And is there any voltage difference between the alternator body and a chassis ground point?
                    The car makes it possible, but the driver makes it happen.
                    Jim Levie, Huntsville, AL

                    Comment

                      #11
                      Originally posted by jlevie View Post
                      With the engine idling, what is the voltage on the exciter stud and what is the voltage on the output stud. And is there any voltage difference between the alternator body and a chassis ground point?
                      The voltage on both studs reads 11.2. The alternator body is grounded. Didnt check the chassis ground point.

                      Comment

                        #12
                        To isolate the problem a little further, remove the exciter lead from the alternator and see what voltage it shows when the ignition is on. It should be at battery voltage. If it is and is at 11.2 when connected to the alternator, either the alternator isn't grounded or the alternator is bad.
                        The car makes it possible, but the driver makes it happen.
                        Jim Levie, Huntsville, AL

                        Comment

                          #13
                          Originally posted by jlevie View Post
                          To isolate the problem a little further, remove the exciter lead from the alternator and see what voltage it shows when the ignition is on. It should be at battery voltage. If it is and is at 11.2 when connected to the alternator, either the alternator isn't grounded or the alternator is bad.
                          Just did what you said. When disconnecting the exciter stud, with ignition on, there is no voltage at all. Output stud still reads 11.2. What does this mean now?
                          Last edited by LuCifer; 03-10-2012, 06:40 AM.

                          Comment

                            #14
                            Bump

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                              #15
                              Swapped out the new alternator for another one. As soon as it was installed Volts were up at 14.1. Car ran great for the rest of the day yesterday, drove home, out at night, drove back home, to work this morning and everything was fine.

                              As i'm leaving work today I notice it seemed weaker on starting up. As i'm driving home the same things start to happen all over again. Any ideas?

                              Comment

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