before i pull the alternator

[Crunchy]

OK four or so months ago the battery on the wife's Navigator died.  I suspected the alternator at first because I had replaced it five or so years ago.  I pulled the alternator (*^($@! and had it checked at Schucks.  They said it tested fine.  I didnt have complete confidence in the new guy running the test.  So I put it back in and bought a new battery (Sears Platium Diehard).  Four months or so later the new battery is now dying.  I charged it today for several hours and she fired right up.  Wife went out for a drive and on the way home the car was dying.  Sounds to me that the alternator isnt charging the battery.  Other ideas before I pulled that sucker out again?  The battery terminal connections are good.

[Heredoggydoggy]

Sounds more like a Voltage Regulator problem.... 

[Skyvalhunter]

you should be able to disconnect the postive  on the battery and the car should run off the alternator. if it dies your alternator is bad.

[Bradyfc]

you should be able to disconnect the postive  on the battery and the car should run off the alternator. if it dies your alternator is bad.

if you do that you take a chance of blowing the diodes in the alternator.

[Skyvalhunter]

Well then you make a suggestion then since you know so much. Meet: You are ignoring this user.

[coachcw]

not a good idea to pull battery cable running , can cause a high voltage issue. through a volt meter across the battery running you should see 14.1 to 14.5 volts then turn on head lamps and heater if voltage drops bellow 13.9 you have a aleternator problem . also verifiy votage at battery vs aternator battery post , they should be within a coupe tenths . most alternators are internally regulated nowdays .

[Crunchy]

Looks like I am going to have to pull the alternator and get it checked again, if (more than likely) it has an internal regulator 

[Bradyfc]

Well then you make a suggestion then!!!!!

i was just trying to save the the guy the extra headache no need taking it personal 

[coachcw]

some thimes when you pull an alternator and check it it will work , like a short brush or connection . run that voltage test if its at battery voltage give the at a tap with a hammer and see if it starts charging.

[huntnphool]

Just check the output of the alternator, on the output post and at the battery with a multimeter. When at the battery check both the battery post as well as the cable connector itself. Test output without any accessories running and then with headlights and heater, wipers etc, for any drop under load. If the alternator/regulator is bad it will be obvious.

[jackelope]

What do you mean when you say the car was dying?
Usually an alternator goes south, battery light comes on, volt gauge drops(if equipped), car runs off the battery till the battery is dead then the car stalls and will not restart. It will have no battery power.
When you say... the car was dying, I think... the car was stalling. An alternator, in my experience, won't cause a car to stall multiple times while driving.

[woowoo]

Sell it, buy a Chevy, and quit going to Schmucks!    Serious though, check the alt. output with a meter.   

[Mudman]

If the alt. you bought 5 years ago was a schmucks.  If so its a concern.

[Crunchy]

Well I made quick work of pulling the alternator and took it to autozone.  They tested it and its fine.  The test they ran also checked the voltage regulator and rectifier?  Anyways they ran it three times and passed all three.  So just finished slapping that sucker back in.  I am going to clean up the battery connections while the battery charges overnight.  See if that may have been it.  If not I am out of ideas.

[Crunchy]

What do you mean when you say the car was dying?
Usually an alternator goes south, battery light comes on, volt gauge drops(if equipped), car runs off the battery till the battery is dead then the car stalls and will not restart. It will have no battery power.
When you say... the car was dying, I think... the car was stalling. An alternator, in my experience, won't cause a car to stall multiple times while driving.

Yes it was stalling and the lights were dimming.  the wife limped it home.  The the battery light came on as well.   I charged it the first time and the battery light went off when it was fully charged.  it was back on when she got home.  The positive terminal connector did not look great.  I will either clean it up or replace it tomorrow.

[JLS]

Replace all the battery cables? 

[jrebel]

Based on your discription, it sounds like an alternator.  I have seen alternators test good when indeed they were bad.  It probably is fine until it draws a huge load.  I would replace the alternator and see what happens.  Alternators are not that expensive....are they?

[Mudman]

Good luck but I still think alt is junk.  Those machines they test with are junk, only work if a catastrophic failure has occured.  It is also possible you will have to replace batt, again as bad alts. have been known to kill good batt.  Charge it up, start it, put meter on batt, check volt. turn lights and everything on and check volts again. if you are in high 11's or low 12's  hmmm.  your battery should always be 12.4 or higher if its good.  IMOP. I just replace my batts in my ford as they were bad.  12.3 volts and 12.8 volts, but walmart and autozone tested and told me yup they are fine.  Napa tested and laughed at my story.  Fixed and no problems last 5 months.

[jackelope]

What do you mean when you say the car was dying?
Usually an alternator goes south, battery light comes on, volt gauge drops(if equipped), car runs off the battery till the battery is dead then the car stalls and will not restart. It will have no battery power.
When you say... the car was dying, I think... the car was stalling. An alternator, in my experience, won't cause a car to stall multiple times while driving.

Yes it was stalling and the lights were dimming.  the wife limped it home.  The the battery light came on as well.   I charged it the first time and the battery light went off when it was fully charged.  it was back on when she got home.  The positive terminal connector did not look great.  I will either clean it up or replace it tomorrow.

How did she get it restarted once it stalled?

[Crunchy]

i dont think it died completly just ran like crap.

[huntnphool]

Sounds to me like a dirty post connection wasn't allowing the battery to fully charge. Clean it up with a little baking soda mixed with water, it will eat the acid away, then use a post cleaning brush for the post and inside the connector.

[jackelope]

i dont think it died completly just ran like crap.

I'm not a tech and obviously cant diagnose it over the www contrary to popular belief, but I don't think your alternator is bad based on your description.
I'd look hard elsewhere. Maybe a connection.

[Crunchy]

Well this morning after charging the battery all night I started the rig up.  Within a minute or two the battery light came on.  I got the volt meter out and got the same reading 12-13volts running and off.  Pulled the battery and had it tested.  Battery was fine.  Put the battery in and drove it to autozone.  They checked the alternator at the battery and showed it was not getting a charge from the alternator.  So pulled the alternator again and replaced it.  No more battery warning light.  Glad I avoided a trip to the dealership.

[huntnphool]

 

[jackelope]

Perfect. Not sure why it would cause the car to run poorly but glad you got it figured out.

[Mudman]

 

[dewandgin]

Well this morning after charging the battery all night I started the rig up.  Within a minute or two the battery light came on.  I got the volt meter out and got the same reading 12-13volts running and off.  Pulled the battery and had it tested.  Battery was fine.  Put the battery in and drove it to autozone.  They checked the alternator at the battery and showed it was not getting a charge from the alternator.  So pulled the alternator again and replaced it.  No more battery warning light.  Glad I avoided a trip to the dealership.

Could you please explain that last Statement?
 We do not charge for battery/charging system test and we check connections also and do a voltage drop. Then if the alt was faulty we would have offered you the choices of having it replaced with a factory part, aftermarket part or not fix it at all and send you on your way.
    Sometimes a faulty alternator will not show up cold as the recitifer bridge solder was probably cracked or cracking and as heat got to it the circuit would have a bad connection.
   

[jackelope]

I think what he's saying is he fixed it himself so he didn't have to take it in to have someone else fix it.
 

[Mudman]

Perfect. Not sure why it would cause the car to run poorly but glad you got it figured out.

I think the PCM is very sensitive.  Some wont even start or run if volts are low even though there is still enuff juice to run em.

[dewandgin]

I think what he's saying is he fixed it himself so he didn't have to take it in to have someone else fix it.

If that's what he meant then that's cool . He just mentioned the dealership instead of a auto repair shop.