Alternator dying???

[bk12321 10+ year member]

Ok, so recently I noticed the voltage on my dash being weird. When you first turn the car on, it will read high 13's, and then about 5 minutes into the drive it will drop down VERY close to 13. Also, a couple days ago I was driving back to school and my car's rpms were jumping at slow speeds (sub 15 mph), and the car would die. It started back up just fine and would run good at high speeds, but when i slowed down again it would start to die. When i have the air conditioning on the car idles fine but when it's off the rpms jump up and down.

Alternator problem im assuming? Im no car mechanic. I thought the battery was dieing at first because of the voltage reading on the dash, but now I'm thinking the alternator isnt charging the battery sufficiently. Also, I would test the alternator but no tools... so just give your best guess and i'll be on my way to Advance in the next week or so //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif thanks.

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[bk12321 10+ year member]

^^^

 

[Frankensuby 10+ year member]

I don't see how it could be the alternator. If you can start it fine right after the car died, your battery is being recharged.

The sign of a dying battery is if the car shuts of non-vital system (ie radio, interior chimes, etc.) and then the entire car shuts off period.

As for voltage, your voltage should read anywhere between 13-15 volts on startup, depending on your stock chargning system. Mine is a standard 14 volt type, or so I assume. You did not post up what the 'normal' voltages were before, this would help.

In essence, the fact that you car is showing lower voltage after a few minutes means that your battery is in fact being charged sufficiently, to the point where the alternator does not see the reason why it should bump up it's voltage/charge to a higher amount. The reason I was told that voltages are high right after an engine start is because the alternator is working harder to replenish energy used to start the car, and also minor drain for sitting overnight.

If your battry or alternator is dying, I believe voltages would actually be higher than lower, or in theory. *IE; the battery is bad, so to charge your entire car and keep it running, the alternator is pushing 16.5 volts to keep everything going)

Maybe another more confident electronic person will step up and fill some details, but this is what i have read and have been told.

PS: your car dying at slow speeds can be alot of things. Maybe a bad 02 sensor causing it to run to rich, or maybe a bad MAF as happens PLENTY in 1st gen Eclipses/Laser/Talons. My Brothers Eclipse would never idle right after he messed up the MAF on a filter change. Just a thought.

 

[phyphoestilic 5,000+ posts]

^^^

good info.

Mine idles at 14.2-14.8 till the engine warms up, then it drops to around 13.8v

When one of my spark plugs got phucked up my car would idle at random RPMs but my check engine light never came out. I only found out about it cuse I just got my car detailed and the guy somehow got water into where the spark plugs were >.

Check that out first. Doesnt sound like a alt problem to me.