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Help please! Voltage Dropping Issue

Discussion in 'VT - VX Holden Commodore (1997 - 2002)' started by MPA, Oct 31, 2019.

  1. MPA

    MPA New Member

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    Hi Everyone,

    Bit desperate here, first time posting.
    This will be a bit of a long post just so I can get as much information out there to help diagnose the issue.

    Car: HOLDEN COMMODORE VX (S2?) 2002 4 Door Sedan 3.8 litre, LN3 (L36) V6

    So my issue is my voltage starts off at 13.5V (Dash Readout) and gradually drops to <11V over time.

    There is no issue getting it started and it always starts with what I believe to be reasonable voltages.

    First sign there is a problem is the Tacko comes and goes and then drops out all-together. Second the music system goes in and out, just the sound over the speakers at first and then the whole head unit starts turning on and off. The ABS light comes on next and headlights get dull. Push it any further and all the dash lights starts coming and going. Eventually the car stalls.

    The Battery Light does not come on until all the light start playing up.

    The voltage drops faster the faster I drive. So 10mins at 60km it's fine, I can get to the shops before I run into major issues. But if I try to drive 10mins at 80km plus it drops much faster.

    What I have done so far.
    1) I replaced the Alternator, this had no effect at all. (Advice from RACQ and Family)
    2) I replaced the Battery. This gave me about 3 weeks with no problems. But they have now returned identical to before.

    I checked with my own multimeter and also had RACQ check and the Alternator and Battery seem to be fine on start-up.

    I have had family suggest the ECU as the next part to replace however reading other posts online, including this forum. It sounds like the issues are too far spread to be the ECU or at least JUST the ECU.

    Any help or advice is much appreciated!
    I'm a bit stressed out at this point.
    I'm worried taking it to a shop is going to be more than I can afford and put me in a bad financial situation but if I get desperate enough it'll happen.
     
  2. lout

    lout Well-Known Member

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    when you see the dash readout being below 13v with engine running
    measure the voltage at battery with multimeter and see if they are close
    symptoms are classic alternator, what alternator did you fit, new, reco, good from wreckers
    is this car electrically stock
    is this car in good condition
    have you checked your ground leads
     
  3. shane_3800

    shane_3800 Active Member

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    I could diag it for you if you were close to me as it sounds like it's an issue on the battery side. The BCM is likely playing up due to the voltage drop So all the cables need to be checked also could be the alt cable. Is the alternator getting real hot? if so its the alt cable.
     
  4. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    AS above, I'd be looking at cables and connections including all earths (engine block, battery and chassis etc). Make sure all connections are tight and clean. Measure the voltage at the alternator from +ve output post to alternator body and then start doing checks between the alternator and battery looking for voltage drops.

    The alternator senses battery voltage via a separate wire that has a fusible link at the battery end, check the link (it may have partially failed leading to high resistance or open circuit when hot).

    The PCM/BCM have no authority over battery/alternator systems (unlike the VE) but they will not be happy with a dropping voltage.
     
  5. gtrboyy

    gtrboyy Well-Known Member

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    Splurge on some new battery terminals then see if still happens.
     
  6. MPA

    MPA New Member

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    Hi!

    Sorry for the delayed reply.
    I think it will be Saturday before I get a real chance to tinker and test but I will try to answer what I can now.

    The Alternator was ordered online from a wrecking yard. They seemed reputable, said it had been tested before sending it. I have a returns and exchange policy I think I might just still be within it if I needed to return it for another.

    Electrically stock. Not really. There is LED lighting strips in the foot wells, a non-stock head unit and an electronic rust protector that may or may not have come with the car originally.

    Car is in reasonable condition, not fantastic but not run down. Previous owners really looked after it.

    I DID test if the Alternator was getting hot. I burned myself touching it after only a 10min drive if that gives any indication? I will check the Alternator plug first and then all the wiring, I can see/get to and checking grounding first thing on Saturday.

    Thanks for all the replies, suggestions and info request so far. Already feeling a bit better about the whole mess.
     
  7. JohnW

    JohnW Member

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    Don't know for sure what the charging rate for a VX should be, but the genuine Holden service manual seems to imply it is the same as a series 1 VT, which is 14.5 +-0.2 volts @20C.

    Buy a $20 Chinese multi meter sold at just about ever auto parts store, even Bunnings. These things are accurate enough for checking battery voltage. Check battery voltage before starting the car, and after starting. If it is 13.5 volts at the battery with the engine running, to me that's a problem.

    If you do decide to replace the alternator, consider you can buy a brand new genuine Bosch alternator (same as original) for around $250?? if you shop around on the internet.
     
  8. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    Anything pre VE the alternators are rated at 14.4 volts (it's stamped on the alternator).

    (using a random interwebs pic)
    [​IMG]
    You can see on the sticker this particular unit is rated at 28 volts and puts out 10amps at it's minimum rpm and a max of 55 amps.

    You can't just say 13.5 volts is an issue as it depends on engine speed and electrical load. At idle with high load the alternator will struggle to keep up.
     
  9. shane_3800

    shane_3800 Active Member

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    Battery initial voltage will affect the the alternator too. If the battery is at like 12.1 it's low on charge so the whole system will have a voltage drop because of the battery.
     
  10. hiker

    hiker New Member

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    A large number of auto electrical faults relate to poor earth/earth return .Perhaps it would be prudent to check the mechanical side of the earth connections - battery to engine,battery to body,body to accessories etc. This can be achieved with the el cheapo multimeter on OHMS scale and the positive side of the battery disconnected. The reading should be 0.3 ohms or less. Maybe temporarily disconnect the rust prevention system. Hope this helps Hiker.
     
  11. shane_3800

    shane_3800 Active Member

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    No this cannot be done with potential you obviously have no idea what you're talking about. It needs to be done with voltage while the car is operational, so you measure the voltage drop under load.
     
  12. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    If you wish to disagree with someone that is fine but please keep it polite. Replies like this turn into **** fights and then I have to ban people.
     
  13. shane_3800

    shane_3800 Active Member

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    Okay sorry, I didn't think I was that unpolite more straightforward not offensive but I'll fairy my comments down.
     
  14. MPA

    MPA New Member

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    Thanks so much everyone.

    I am kinda pumped to go crazy with my multi-meter tomorrow.
    I'll test things before and after I adjust any cables/connections and hopefully will be reporting good news or data that's helpful for diagnosis.

    I'm glad I was recommended to these forums.
     
  15. JohnW

    JohnW Member

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    At the auto electricians just a couple days ago. To test the alternator he simply turned the air conditioner and headlights (high beam) on, and it showed 14.5 volts at the battery at idle (slightly elevated due to the air conditioner and termo fans running).

    The battery was at a normal state of charge.
     
    Last edited: Nov 2, 2019
  16. MPA

    MPA New Member

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    Didn't get far today as I'd like but here is what I have to report.

    Multi-meter on the battery terminals when not running returns ~12.5V. This matches the battery test that supercheap auto did when they sold me the battery, I went and found the paperwork and double checked.

    Car running idling in the driveway gives 14.25V at the battery terminals. The Cars dash was reporting 13.0V.

    I checked every fuse and relay and found that the Engine Cont Relay was looking in bad shape.
    Picture attached:
    75552823_450413532261783_2322753695617384448_n.jpg

    I replaced it and then took the car out so I could do post run tests.
    (Which were planned prior to finding the relay in bad shape)

    During the run the voltage on the dash stayed around 13V even at higher speeds (80-100km/h) where it was rapidly declining previously. I still had my sound system dropping in and out though. During heavy acceleration the voltage dropped down to ~12.5V and gradually returned back to 13V. Which again is new, usually once it drops it just continues downwards to 11V or so and then everything goes nuts. It also dropped a bit when ghosting down hills and then returned. Still the audio was playing up but the Tacko was fine the entire ride which was previously the first thing to mess up.

    At home in idling in the driveway after the run Battery terminals have 14.0V which slowly dropped to 12.5V once the car was turned off.

    The Engine Cont Relay was extremely hot to the touch after the drive. Inside the car the Blower Relay was also pretty hot but not as bad. I turned off the fan and the dash began to read 14V, tested the terminals and it also had 14V so they were agreeing for the first time so far.

    I'm going to take it for another short run now without the blower running and see what happens.

    I know there was a lot more advice given and questions asked and I do plan to get to them, this is just my very first steps. My multi-meter was dead this afternoon and the one place locally that stocks them (Our tiny bunnings) was out of stock so I had to wait around for a loan of one and thus didn't get much done today. Sorry!
     
  17. the_boozer

    the_boozer no more VK

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    How tight are the connectors in the relay socket loose connection getting hot ?
     
  18. shane_3800

    shane_3800 Active Member

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    Sounds like there's an issue between the fuse box and interior.
     
  19. lout

    lout Well-Known Member

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    with engine running try measuring around the fuse box under steering column and see if there are any clues
     
  20. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    Definitely an issue somewhere between the battery and the interior.

    If you can work out what circuit/accessory is causing the voltage drop it'll make it easier to locate the problem.
     

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