alternator or starter?

[92doorblazer]

Long story short,

92 Full size blazer, 5.7

Yesterday battery was fine. Today, slow crank this morning. Each time after that cranking/starting gets slower and slower. Until finally nothing. Checked all the battery connections no corrosion but cleaned them just in case. Still nothing. The truck WILL start with a jump however. Jumped it twice today an both worked.

Voltage meter reads normal when driving, HOWEVER, while turn signals are ON tachometer and voltage meter both bounce and spike with the blinker.

I got home about an hour ago and put the battery charger on it. Charger says battery is fully charged. Try to start it , weak crank till eventually no power/no dome lights. Nothing.

Oh BTW i didnt trust the charger only, had the battery tested at walmart and saw the paper read 12.7 volts.

So starter or alternator?
P.S. this sucks

[kcb37]

Test the power at the battery, and at the starter. This will tell you the condition of the battery cables.
If they have a big drop in power, replace them. If they are factory or as far as you know replace them.
Other then that, have the alt tested too.
Also make sure you have a good ground.

[stupid friend]

altenators should put out about 14 volts while running, if it is less than that, replace the altenator, or you can take it out and have Autozone check it for you.

[desrtrat]

while your at Auto Zone bring your battery in and have it load tested it can show 12v at the terminals, but if you only have 250 amps stored, then time for a new battery, probably have a dead cell

[00_chevy_2500]

If it tested 12.7 volts it should be the starter. Just had the same problem with my s10 last month. It would crank fast, then slow, then stumble and start after 20 seconds. haha

[stupid friend]

Originally Posted by 00_chevy_2500

If it tested 12.7 volts it should be the starter. Just had the same problem with my s10 last month. It would crank fast, then slow, then stumble and start after 20 seconds. haha

But that is with no load, you need to do what desrtrat said, have them load test it. As a matter of fact I think you can take the truck there and they can test everything right in the truck. It would keep you from from taking out one component at a time

[Hodges87]

Originally Posted by desrtrat

while your at Auto Zone bring your battery in and have it load tested it can show 12v at the terminals, but if you only have 250 amps stored, then time for a new battery, probably have a dead cell

Great advice, also have them test your alternator while your there.