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Thread: Alternator issues? Need some help

  1. #1
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    Alternator issues? Need some help

    Shredded a belt about a month ago, alternator and water pump. Got a shop to replace it since I was a about 45 min from home. There was a bit of a whine after some work I did that seemed to go away with the new belt, but the shop said the alternator was bad, and the cause of the belt failure. They said they could feel the pulley sticking due to bad bearings, I couldn't feel anything when I inspected it. As the car has 228k I decided it would be prudent to change anyway. I bought a Power Select new alternator from Rock auto and replaced it and 2 new belts about 3 weeks ago. a week ago both headlights went out, then last night after getting above 5000rpm I had some new issues. I was accelerating quickly to merge on the interstate and hit about 5300 rpms and my alternator light came on and my fans got loud and faster than I've ever seen which lasted about 1 min. It was dusk and I had my lights on, but didn't notice till dark that both headlights were out (no other lights that were on were affected). Found that both filaments were melted. Could I have gotten a faulty alternator? Might it be something else? A few things about my P5, 2003 5sp with 228k, replaced heads in march and removed VTCS and installed a MP3 ECU, water pump and thermostat changed last october. Other work includes a clutch last year and motor mounts and coilovers. Any advice would be appreciated.

    Thanks
    Last edited by emersonlennon; 08-18-2017 at 01:53 AM.

  2. #2
    Certified Mazda Tech hornsfan10609's Avatar

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    The ECU regulates the alternator voltage. Are the connections at the alt secure? Any wiring damaged/grounded out? It's not uncommon for P5 headlight bulbs to fail, but it sounds like your system is surging voltage. It will start popping fuses if it continues, but the battery light will only illuminate when the voltage spikes or is too low.
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    The Diagram Dude pcb's Avatar

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    I think your alternator is bad...
    I'm almost positive that if the control wire has a bad connection, is broken or is shorted out, the alternator effectively shuts off, it won't go to maximum output.

    I had one of my alternators go bad, the battery light came on and stayed on and the voltage shot up to 17 V.
    I turned one every electrical load to lower the voltage and drove it to the shop where it was replaced under warranty.

    Did your battery light stay on ?? Or was it only on for that minute.
    The Diagram Dude

  4. #4
    The Diagram Dude pcb's Avatar

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    This is the schematic for our alternator... The LG/W wire (light green with a white stripe) is the control wire hornsfan mentioned.

    The ECU sends a varying voltage through that wire which turns the output of the alternator up and down.

    I'm thinking the ECU knew the voltage was too high (hence the battery light) and tried to turn it down but the alternator didn't respond.


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  5. #5
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    Quote Originally Posted by pcb View Post
    I think your alternator is bad...
    I'm almost positive that if the control wire has a bad connection, is broken or is shorted out, the alternator effectively shuts off, it won't go to maximum output.

    I had one of my alternators go bad, the battery light came on and stayed on and the voltage shot up to 17 V.
    I turned one every electrical load to lower the voltage and drove it to the shop where it was replaced under warranty.

    only came on for that minute

    Did your battery light stay on ?? Or was it only on for that minute.
    it was only for that minute or so
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  6. #6
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    Quote Originally Posted by hornsfan10609 View Post
    The ECU regulates the alternator voltage. Are the connections at the alt secure? Any wiring damaged/grounded out? It's not uncommon for P5 headlight bulbs to fail, but it sounds like your system is surging voltage. It will start popping fuses if it continues, but the battery light will only illuminate when the voltage spikes or is too low.

    I'll get in there and make sure nothing came loose on sunday, thanks for the advice
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    I've been having the same issue with my car and I checked all the connections replaced the alternator and battery twice and now I have almost no functionality out of the wire harness inside the car.

  8. #8
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    pcb is correct. while the ECU has an output that is supposed to control the alternator, the regulator is built into the alternator. If the regulator goes bad it will spike voltage through the roof and cause all sorts of bad things to happen... blown bulbs, etc. potentially it could also damage computers or more sensitive electronics in the vehicle. i wouldn't drive the car until you get it fixed.

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    Quote Originally Posted by pcb View Post
    This is the schematic for our alternator... The LG/W wire (light green with a white stripe) is the control wire hornsfan mentioned.

    The ECU sends a varying voltage through that wire which turns the output of the alternator up and down.

    I'm thinking the ECU knew the voltage was too high (hence the battery light) and tried to turn it down but the alternator didn't respond.



    Still been having the issue. I have more detail though. The manufacturer is blaming the ecu though I didn't have the issue before installing a new alternator, but I am running a used mp3 ecu, but they are not aware of that. Ive double and triple checked the connectors and wires and found no issues. I have found that if I get above 4k rpm for more than a second I will feel a spike in voltage but not enough to kick the warning light on, if I get above 5k rpm for more than a second the spike is enough to turn the warning light on. I have also found that if I take it out of gear and release the clutch the voltage will return to normal. I still feel like its the alternator, but will put my stock ecu back in to test. whats the best way to get my old alternator inspected to see if its working properly and if the bearings are ok? any other suggestions
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    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by emersonlennon View Post
    ... I have found that if I get above 4k rpm for more than a second I will feel a spike in voltage but not enough to kick the warning light on, if I get above 5k rpm for more than a second the spike is enough to turn the warning light on...
    That's your alternator... It's screwing up.

    I'm 90% sure your alternator is bad..
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  11. #11
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    Follow up: Ordered a replacement alternator, once I had the cash and installed it about a month ago. Only issue since has been that lights will occasionally dim at idle for a split second. This happens even without the A/C running, but I don't think its an issue or anything I should be worried about since most cars I've ever owned have done this. Thanks everyone for the advice and support. I am loving this community!
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