Diming Lights and loss of Power in 91 Testarossa | FerrariChat
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Diming Lights and loss of Power in 91 Testarossa

Discussion in 'Technical Q&A' started by Shamile, Jul 15, 2006.

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  1. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,712
    Lakeland FL
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    Shamile
    #1 Shamile, Jul 15, 2006
    Dear Ferraristi,

    I had the Testarossa out last night to do the groceries. I was driving along and noticed as I would come to a stop, ( clutch in ) the revs would drop off and and the tach needle would bottom out and then come back up. It sounded like the engine was stalling out. More traffic lights later, the same but a few times now, the engine stalls. ( easy start right away) I then notice as I come to a stop (low revs) the dash light lights are going dim. When I take off I notice an extreme lack of power. I get to the supermarket, rev the engine, sounds good and idle is smooth) I swear a hear a slight whine from the engine area. The alt is still turning. I turn the engine off, start it up....no problem. Ok, do the groceries, come out, start up, no problem, full power. I get close to the house, lights start to dim again when the revs drop off, again engine sounds like its going to stall and the revs jump back up. Clutch in as I pull into the driveway, and revs bottom out and stalls...again starts up fine.

    I get it in the garage ( ice cream in freezer first ) and put my volt meter on the battery. Full lights and fog lights, 13.2 volts. If I rev the engine, the volts go up and down and the lights dim slightly and come back as the engine revs bottom out and come back. I turn off the engine, 11.78 volts on the battery. A while back I did this test ( looking for another problem ) and the volts at the battery were 14.2 with the engine running and full lights on or off. Reving had no effect...14.2 all the time.

    This time with the lights on or off, there is a difference in the reading at the battery. I also noticed, if all lights are on and I rev the engine, the revs drop off and bottom out, sounds like it may stall and comes back. If I turn the lights off and rev, the revs drop as normal, no "winking out"

    My thinking is the alternator and or battery. I know from my experience that a bad battery will ruin an alternator and a bad alternator will ruin a battery. I will change both.

    I was just wondering, is there anything elce I should check out?

    Any help would be greatly appreciated.


    Shamile

    Freeze....Miami Vice !
     
  2. PAP 348

    PAP 348 Ten Time F1 World Champ
    Lifetime Rossa Owner

    Dec 10, 2005
    100,232
    Mount Isa, Australia
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    #2 PAP 348, Jul 16, 2006
    You almost lost me there in your post Shamile. :) I think you have all bases covered at the moment mate. Before you replace anything mate, my suggestion would be to remove the battery from the car and get the battery load tested 1st at your local parts shop or mechanic, or whoever has a battery load tester. If the battery is ok, then I would remove the alternator and get it load tested at a good Auto-elec workshop. They should let you know of its condition. Give that a go 1st and see how you go. :)
     
  3. Magnum6464

    Magnum6464 Formula Junior

    Mar 5, 2006
    319
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    Mario
    #3 Magnum6464, Jul 16, 2006
    You have a short or bad ground in your lights somewhere, remove all light fuses and test one at a time. your alternator works and so does your battery. Batteries and alternators are like flat tires, they are either flat or not. Also ask someone to observe your lights as you play with them, signal, brake, reverse etc...to see if anything weird happens like pressing on the brake with the flasher on and the brake lights go out, or when you brake your reverse lights go on and stuff like that....

    Oh in case your asking how I know your alt and batt are good, well you said it yourself, when driving...full power no issues (alt giving good power) or else you light would dim slowly and you car would come to a dead halt because it was running on the batt (because the Alt failed). Also you started your car 5 times and had no issues...your batt is good. Or else you would of notice a significant decrease in starer motor power from one start to another.

    Find your short and dont drive with your lights on until then or you will fry your Alt...

    Good luck and keep us posted.....
     
  4. Boxer12

    Boxer12 Formula 3

    Jun 1, 2003
    1,672
    #4 Boxer12, Jul 17, 2006
    Do you have the same problem in daylight with lights off? Also, test the alternator output with a multimeter (if you don't own one, it would be a good time to get one...maybe save you a few hundred in diagnostic costs at the dealer). Test voltage with the motor off and then running and see if there is a jump. Try it with lights on.

    You can quickly test for a short by removing the pos battary cable (charge the battery if nec) then by holding it close to the post and see if a spark arcs to it. If so, you have a short.

    It doesn't sound like a battery, and unless the alt just failed abruptly, you would expect the battery to go out with the alternator. FYI, the alternator can be rebuilt, which is a lot cheaper than replacement and works fine. Jim
     
  5. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
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    #5 Shamile, Jul 17, 2006
    Dear Ferraristi,

    Thanks for the advice. A couple of things though:

    When I was driving, the lights would start to dim as I was coming to a halt. I mean really go dim. As soon as I accelerate, they would come up to normal.

    I got a big power loss when I tried to "gun" it. After, I came out of the supermarket, all was fine untill I got close to home, (a few miles ) and the lights would go dim and start this all over again.


    I was driving about 3/4 hour before this all this happened. ( 5 minutes from the supermarket )

    I will get things load tested as ya'll advised but is there anything else I should check out ( specific relays on board ?)

    Thanks again,


    Shamile

    Freeze....Miami Vice !
     
  6. Shamile

    Shamile F1 Veteran

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    #6 Shamile, Jul 17, 2006

    Dear Ferraristi,

    I do have a multimeter. How do I check alternator ouput, what setting on the meter and what would be considered a good reading?

    Please let me know.

    Shamile

    Freeze....Miami Vice !
     
  7. Shamile

    Shamile F1 Veteran

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    #7 Shamile, Jul 18, 2006
    Dear Ferraristi,

    One point I need to make is that when I said power loss, I meant HP not electrical power. Would this loss of HP be related to a dying battery or Alt?

    Please let me know. :)

    Shamile

    Freeze...Miami Vice !
     
  8. Magnum6464

    Magnum6464 Formula Junior

    Mar 5, 2006
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    Mario
    #8 Magnum6464, Jul 20, 2006
    Batteries are only needed for starting, so if it always starts good, look elsewhere. Your losing power (HP) your plugs are demanding it from your alternator when you gun it, but if you have a short somewhere your robbing power to your plugs. Now when you were getting power loss, was this only when the lights were on ???
     
  9. Boxer12

    Boxer12 Formula 3

    Jun 1, 2003
    1,672
    #9 Boxer12, Jul 20, 2006
    You use the DC Volt setting on the dial at "20". Put the black on the neg batt terminal and the red on pos. Check it with the car off, the battary pos disconnected for a pure battary reading. It should be 12V or something close to it. Then hook up the pos cable and see what it reads. Again, it should be close to 12V. Start the car and see what it reads. Turn the lights on, and it should go up a bit, demonstrating that your alternator works.

    If the batt starts out low, unhook the pos and charge it and see if it will get up to 12V. If not, it is prob bad. If so, but then it drops when you hook up the pos, then you have a short. Also, look for a spark when you hold the pos close to the post. A slight spark is normal, but only 'slight'.

    If batt is ok, but no you get a lower reading when you start the car and turn the lights on, then your alt needs to be rebuilt.

    Jim
     
  10. Shamile

    Shamile F1 Veteran

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    #10 Shamile, Jul 23, 2006
    Dear Ferraristi,


    Thanks guys!. I will be diving into this tomorrow ( Sunday) . I'll let ya'll know what I find out.

    BTW, I couldn't tell you if the ( HP ) power drop was only with the lights on. I was driving at night and didn't think about checking that out.


    Shamile

    Freeze...Miami Vice !
     

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