Help me understand the charging system in our cars
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Thread: Help me understand the charging system in our cars

  1. #1
    JUNIOR ROVER
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    Help me understand the charging system in our cars

    Well a 1999 Gems 4.0s. My Autozone Duralast yellow top battery (8 months old) has been dying at least once every 3 weeks to the point that starter motor nolonger turns. Couple of days ago I changed the battery to one of their Platinum series (AGM) one and that one died almost a day after and then again today. I started looking closely in to whats going on and found the Negative wire that connects to the Alternator bracket was hanging loose. I may have forgotten to connect it after doing the heads. I'm thinking this is the culprit that is causing the battery to not charge. Can't tell for sure till I recharge the battery again.
    Even tho the battery is not completely dead (lights work, no dimming of dash lights, Battery voltage around 12.8v) what causes the car not to turn the starter even when using my Duracell Orange starter pack nor trying to jump start it. I noticed that before it died the other day, the starter would turn and the engine won't start as if there is no spark.
    Once the Baterry is charged all is back to normal.
    Is this the work of the BCM to shut the system off when there is no sufficient charge from the battery? Including been able to jump start?
    If the old yellow top to took 3 weeks to discharge and the new AGM one only takes a day, will I be better off with the old baterry?
    Again, I'm hoping that the issue was with the ground and all be sorted once the battery is charged.
    At the same time, just want to overcome that helpless feeling of being stranded in 100f+ temps.
    Dinesh H
    1999 Range Rover 4.0S
    2001 Mercedes ML320
    1993 Mercedes 190e 2.6
    1985 Mercedes 190e 2.3
    1983 Mercedes 380SEC
    1974 FIAT Spider

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  3. #2
    FORUM MODERATOR RRToadHall's Avatar
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    Re: Help me understand the charging system in our cars

    You can replace the batteries until you are blue in the face but it won;t do any good if your alter nator is failing, you have a duff cable, corrded connection etc. You could also have a power drain from stray radio signals keeping your BeCM awake or a dirty relay. As far as the actual charging circuit have you completed the tests in the electrical stickie above?
    When dealing with yourself, act with your brain
    When dealing others, act with your heart.

  4. #3
    JUNIOR ROVER
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    Re: Help me understand the charging system in our cars

    The Alternator was rebuilt a month ago and was tested again a couple of days ago. As I said, the ground strap to the Alternator bracket wasn't connected after the heads were installed and that was when my troubles began.
    There may be more than one issue at play here. I will test Relays 16 and 12 today.
    Dinesh H
    1999 Range Rover 4.0S
    2001 Mercedes ML320
    1993 Mercedes 190e 2.6
    1985 Mercedes 190e 2.3
    1983 Mercedes 380SEC
    1974 FIAT Spider

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  6. #4
    FORUM MODERATOR RRToadHall's Avatar
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    Re: Help me understand the charging system in our cars

    aky... but have you done the tests in the stickie above. There is more to a charging system than just an alternator.
    When dealing with yourself, act with your brain
    When dealing others, act with your heart.

  7. #5
    JUNIOR ROVER
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    Re: Help me understand the charging system in our cars

    Just an update to this thread if anyone ever come across it; no starter issues whats so ever after connecting the ground strap to the Alternator.
    Dinesh H
    1999 Range Rover 4.0S
    2001 Mercedes ML320
    1993 Mercedes 190e 2.6
    1985 Mercedes 190e 2.3
    1983 Mercedes 380SEC
    1974 FIAT Spider

  8. #6
    SENIOR ROVER
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    Re: Help me understand the charging system in our cars

    Phew!

    Glad you found it.
    2001 HSE "Sandy"on air.

  9. #7
    Premium Member Escape's Avatar
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    Re: Help me understand the charging system in our cars

    Quote Originally Posted by desertboy View Post
    Just an update to this thread if anyone ever come across it; no starter issues whats so ever after connecting the ground strap to the Alternator.
    Good to have closure on this thread. However, just because the ground strap is attached to the alternator, doesn't mean it was the alternator that was at fault. Both alternator and starter motor are connected to the engine block, so the starter could use the same ground if there is no better one available.

    Filip
    4.0 SE manual, 1997, 'Priscilla': current daily
    4.0 SE manual, 1995, 'Piper', built for offroad with tuned 4.6 on MS: lost in fire
    4.6 SE auto, 1995, 'Prue': awaiting attention
    2.5 DT manual, 1996, 'Paige': retired and stripped
    D90 TD5, 2005, 'Nessie' TR2 racer: sold

  10. #8
    FRESHMAN ROVER
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    Re: Help me understand the charging system in our cars

    Regular ground strap connection cleaning and protection along with verication of conductivity is an important aspect of servicing vehicles of a certain age. Factory plating and joint protection begins to deteriorate noticably towards the end of the first decade so it gets harder for the high current demanded by the starter to flow. It can also affect the voltage level sensed by various electronic components which can affect how things behave or throw fault codes. This latter is especially important on our P38 range Rovers which fundamentally were designed with too low a voltage noise margin making the electronics overly sensitive to volt drops and shifts from poor connections. ( In my view if all the clever stuff had around 6 volt noise margin most of the tricky electronics problems wouldn't happen.)

    Starter current will find whatever path it can. Usually there are several possibilities so a good deal of degradation can occur before things really fail. Sometimes the last alternative path can be embarrasing. For example I had the earth strap fail during a journey on aold type SAAB 900 auto. On start up to go home the starter return path went through the gear selector cable heating it up enough to melt the nylon liner locking things Park. I shudder to think of the electonics damage a similar failure could do to a P38!

    Bosch alternators do not like crappy earths. Charging voltage can be all over the place and the controller can be damaged. Worst point is it can partially fail so things appear to work but the actual charging behaviour is wrong killing a new battery in a few months. Sensible man fits a quality service exchange alternator if you have troubles with an alternator that has gone beyond around 100,000 miles.

    Clive

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