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    Intermittent Alternator?

    So I drove my 325e to a muffler shop for them to take a look at the exhaust leak present in my downpipe. It was too close to closing time and they said to come back on Monday, which is fine.

    But then my car wouldn't crank over. Starter motor tried its hardest, but it wouldn't start. Brand new battery. Got the shop to jump me, idled it for a minute, and drove it back to my apartment as quickly as I could.

    The idle was high at like 1100 rpm (which I've had trouble with before) the entire time, and I had basically no torque at all. Near the end, I noticed my tach would just blink out to 0 rpm even though the engine was still running and then cut back in.

    Get it home and it starts knocking. Get out my DMM and the battery at the terminals with the car running was at 10.5 volts. Balls.

    Turn the car off and shut the windows/sunroof, pulled the battery, and plopped it on the trickle charger. Held a full charge on it for a bit, so the battery is still good. Put it back in, wait for the awful ICM to learn how to idle again after 5 cranks, and measure the terminals again. 13.6 volts. Lights on, radio on, blower on, 1500 rpm, read 13.45 volts. Huh...

    Take it for a gentle spin around the block, and it starts idling high again. 1100 rpm. Park back at home, measure battery, 11.5 volts...

    Do I need a new alternator? Voltage regulator brushes? I may as well throw a new alternator in there. This one looks like it came with the car.

    Thoughts?

    #2
    Have the alternator tested at a major parts store?

    [IMG]https://cimg4.ibsrv.net/gimg/my350z.com-vbulletin/550x225/80-parkerbsig_5096690e71d912ec1addc4a84e99c374685fc03 8.jpg[/IMG

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      #3
      Check the voltage regulator first before take the whole alternator out. Most of the time, replacing the brush would take care of the problem.

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        #4
        Figuring that the thing was 35 years old and probably at the end of its life, I went ahead and yanked it out anyway. Holy crap I have never seen so much road dirt soaked in engine oil and grease. Felt more like being a gardener than a novice mechanic.

        I took my filthy alternator to O'reilly and one of the guys there tested it, and it passed twice. Good news! I don't need to buy a new alternator. Bad news! I still don't know what's wrong. May as well overnight a new regulator anyway, while I've got it out.

        I sprayed the ever loving piss out of the alternator bracket with brake clean, and took off the motor ground and the ground cable leading from the alternator to the bracket (weird that this is there, but whatever, I'm not an engineer). I used the rest of the can of brake clean and a wire brush to clean up the alternator case, focusing on the surfaces that mate to the bracket.

        The insulation on the alternator ground cable looks like someone stuck it in a toaster oven and set it to "STAR CORE" and then went to bed. Going to go ahead and make a new one. I've needed an excuse to buy a pair of terminal crimpers for long enough.

        By that time, the parts store had closed, so I'll go tomorrow and buy the required wire and terminals. I also bought a new belt, but it looks like you have to take off the AC and PS belts to change it. The tension adjuster was maxed and I could still spin the pulley. No bueno.

        Someone's also clearly had a go at this before, because the teeth on the adjuster nut had some teeth missing ;D.

        Feels good to get my hands dirty. Most of you could probably do this with your eyes closed, but this is the most work I've done on a car myself yet.

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          #5
          If it is good I'd look at the grounds. They go bad, I just replaced/upgraded all mine as PM.

          [IMG]https://cimg4.ibsrv.net/gimg/my350z.com-vbulletin/550x225/80-parkerbsig_5096690e71d912ec1addc4a84e99c374685fc03 8.jpg[/IMG

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            #6
            On Parker's advice, I ordered a new alternator ground cable and engine ground cable. It took a breaker bar to get the old ones off. While I was at it, I spent $38 on the 3 screws that hold the AFM onto the bracket because the old ones were dry rotted and sheared off. Also put in a new intake boot because the old one was hard and cracked.

            Otherwise, y'all were right. Alternator voltage regulator brushes were nubs. One of them was pretty severely notched. Hope that won't end up being an issue.

            New belts, voltage regulator, ground straps, and some tidying. I turned everything on, screwed the throttle cable to hold at 1500 rpm, and there's solid 13.7 volts at the battery terminals. Victory. At idle with everything on, it bounces around a little at 13 volts. I let it idle for about 10 minutes and then took it for a brisk spin, tested it again, and the reading was consistent.

            Feels really good to fix something.

            Now for that exhaust leak...

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              #7
              Well, it started idling high again so I got out and checked, and the battery was back down to 11.7 volts with the car running. Rushed it home, lights started to dim out. Same story. Turned it off and tried to crank it again and it wouldn't turn over.

              Voltage regulator is new, grounds are new, belts are new, alternator tests working. Not sure where to look next.

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                #8
                I think you were on the right track with 35 years old. I say replace the alternator with a proper rebuilt one.

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                  #9
                  So I looked at the wiring diagram, and I thought I had found a short. I pulled the gauge cluster and was testing between D+ on the alternator (this is the exciter wire and should read battery + for anyone reading this in the future) and the same pin on the connector by the fuse box. One read with continuity and the other read 16.8k, which isn't right I don't think.

                  I pulled my battery warning light bulb (which is necessary for the charging circuit, again for anyone reading this in the future), and tested it with a known 12 volt source, and it was a good bulb.

                  I poked around under the dash and didn't see anything with shit stains on it like a short grounding out.

                  Then I decided to test if there was voltage getting to the cluster pins that lead to the bulb. I put the battery back in, jumpered pin 14 and 16 on the blue connector (which are the bulb pins; look at the diagrams for your car), turned the key to accessory, and... Battery voltage. No way, wait what? Plugged the cluster back in and the light worked! No way!!

                  Put the battery back on the charger until it was full, put the dash back together, put the steering wheel back on (yay torque wrench), sew everything up, and sure enough. Near as I can tell, it's sorted. I drove it around on several short trips, testing the voltage between Alternator V+/D+ and ground at the diagnostic port, and it was holding strong. A slightly noisy 13.8 volts.

                  I don't know what the hell I did but it seems to be fixed. My guess is that when I had previously pulled the cluster to change the odometer gears, I must have knocked the battery lightbulb socket on something and bent the tabs on the socket. I must have pulled it out to check the bulb, and put it back in correctly. I kind of don't trust this alternator anymore though, so I'll be looking to replace it when I have $200 to spare.

                  This has been such a pain that I'm thinking about installing a battery voltage meter that's independent from the charging circuit. Anyone know a neat way to do this? Thinking about going to a junkyard and finding some random dash cluster, pulling the galvanometers out of some random gauge, and 3D printing some kind of housing bracket to mount maybe near the headlight switch or something. Maybe something small like a repurposed fuel gauge.

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                    #10
                    Several members on the board sell volt meters. You can buy one from amazon and make your own or just get a cigarette outlet voltmeter w/USB port.

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