Mystery voltage drop problem. Need help.

[SS_Sean]

This has happened three times to me now. I topped off my battery on a trickle charger last night and took the car out. I was specifically monitoring the scanmaster for voltage. I drove the car out a couple miles down the highway and within just a couple miles the voltage went from 13.8 to 10.8 volts. The headlights dimmed and I turned around and immediately started heading back to town. By the time I got to town I had to turn my headlights off and the voltage had dropped to 9. I barely made it home.

Now I have previously had the battery and regulator checked under load, and they 'appear' to be working.

At this point I'm at a bit of a loss.

 

[BetMinesFaster]

Sounds like a failed alternator. run the car warm, check to make certain at the plugin on the back of the alternator that there is battery voltage, if so test the volatge at the large stud on the alternator, running it should be around 14, if not you likely have a bad alternator...It would not be uncommon for an alternator to charge when cold but tucker out when it warms up....also follow the large wire from the alternator to the starter, make sure its in good shape and that the fusible links at the starter are all in good shape....also follow the positive cable down from the battery to the starter, the positive cable was common to ground out causing problems as well....Hth, Ryan

 

[Boost231]

Sounds like a failed alternator. run the car warm, check to make certain at the plugin on the back of the alternator that there is battery voltage, if so test the volatge at the large stud on the alternator, running it should be around 14, if not you likely have a bad alternator...It would not be uncommon for an alternator to charge when cold but tucker out when it warms up....also follow the large wire from the alternator to the starter, make sure its in good shape and that the fusible links at the starter are all in good shape....also follow the positive cable down from the battery to the starter, the positive cable was common to ground out causing problems as well....Hth, Ryan

+1 good advice here.

 

[BetMinesFaster]

Thanks boost.... Have I ever mentioned that id like to flip your car over and eat off the bottom!!! yours looks nicer underneath than mine looks on the shiny side!!!

 

[SS_Sean]

Alright you two...get a room.

Battery postive and negative cables are new. Inspected starter wiring yesterday. I'll look at the alternator wiring this weekend.
Thanks.

 

[BetMinesFaster]

Yuppers......thats what your turbocharged buddies are for!!! Oh, Would you like to join us in this room Lol

 

[turbocam]

my alt. had a worn bearing ,did about the same thing as yours.it would drop down around 11,then spike up to 15.9 new alt. my problem solved:biggrin:

 

[jhanson1750]

Sound like either the alt failing under a load (once it warms up) or a wiring issue. Both were described above very well. Get out the trusty volt/ohm meter and either start at the alt or the battery and check the wiring out one section at a time for continuity. Also check it and then "wiggle" it and check it again. Could be an intermitteint open in the wiring. Good luck Jon Hanson

 

[emangn1]

im new here but some times i teach the instuctors at gm class this is the season for dead cells in batteries seen 2 this week each cell is 2.2 volts and anything under 10 has a bad cell or a high amp draw there is no way if the voltage drops from 13 or so to 9 to be a alternator 13 to 12 then 11 to 10 could be alt.. but not suddenly unless high amps came in like my truck had a stuck cooling fan motor didnt blow the breaker but pulled 30 amps off battery but still only fell to 12.6 volts . if you have your batt in the trunk sideways and drag frequently the plates will hit each other on launch causing the link between the plates inside the batt to fail . load check the battery with a vat 40 not the tester at autozone most shops will do it free i love killing batterys for customers at 300 amps to see if they fail also check your cooling fan becouse you were into a drive cycle long enough to turn on
hope this helps big E

 

[Turbo1dr]

One other suggestion...turn the key on/engine off and see if the idiot light lights up. If it does not check that for connection issues or blown bulb.

 

[David65]

One other suggestion...turn the key on/engine off and see if the idiot light lights up. If it does not check that for connection issues or blown bulb.

Exactly. Key on with the engine off, alternator light should be on. If not, pull the 4 pin plug from the rear of the alternator and ground the brown wire in the L position. If the light does not come on, problem is in that circuit, possibly the bulb or its connection into the instrument cluster.

 

[SS_Sean]

What do you mean by 'If not, pull the 4 pin plug from the rear of the alternator and ground the brown wire in the L position'? What is the 'L position'?

 

[David65]

What do you mean by 'If not, pull the 4 pin plug from the rear of the alternator and ground the brown wire in the L position'? What is the 'L position'?

If with the ignition key in the run position and engine not running, the alternator light on the dash should be on. If it isn't on, unplug the 4 position (regulator) plug from the back of the alternator and use some wire to short the brown wire in the L position to ground. The L refers the the Lamp lead, which is the brown wire that goes to the dash light. The 4 spots in the plug are labeled P, L, F, & S.

 

[MeanBuicks]

Try this.

Oh heck. Looks like David came up with a better image.

 

[SS_Sean]

Ok. Will get some checks done. Thanks for the heads up...

Frankly...I can't even remember if the red 'volts' light comes on or not. It's like that yard gnome in your front walkway. Was it there today when you got home, or did some kid steal it? :biggrin:

 

[84HAGN]

MIne did the same thing

Check this post mine was doing the same thing :
http://www.turbobuick.com/forums/hot-air-non-intercooled-tech/226770-knock-problems-solved.html

 

[84HAGN]

MIne did the same thing

Check this post mine was doing the same thing :
http://www.turbobuick.com/forums/hot-air-non-intercooled-tech/226770-knock-problems-solved.html

 

[SS_Sean]

Just to confirm, the plug in the picture above only has one wire coming out of it, and that is the brown wire in the "L" position, right? The only other wires attached to my alternator is the positive lead from the the battery to the back of the alternator on the post, and the hot lead from the post on the back of the alternator to the fuel pump. There are no other wires attached to this alternator. Confirm this wiring is correct, please.

Also, the red 'volts' light is lighting up in the dash with key on/engine off.

I purchased a new alternator and when I start the car I'm reading 14.7 vdc at the battery. I'm reading 14.6 vdc at the back of the alternator, and I'm reading 14.5 vdc at the scanmaster.

 

[SS_Sean]

Okay...took the car out for a spin with the new alternator. The red 'volt' light lights up in the dash on startup. I drive around for a bit and let the car warm up. I see the volts go to 13.8 and then start creeping down to 13.4, then all the sudden it dips to 11.2, and then starts bouncing around 10.8, 10.2, 13.5, 10.8, etc., etc. I drove the car home and parked it in the garage, shut the motor off and observed the red 'volts' light does not light in the key on/engine off position.

 

[84HAGN]

Check My post

Same thing mine was doing check my post