Another alternator problem... help me trouble shoot please.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
With a DMM set to VDC, measure the voltage across the following, with engine running:
- battery negative post and engine block;
- battery positive post and alternator post;
if you see more than 0.3V across either of those, then you have to look at the cable and its connections to see if they are corroded (or otherwise have high resistance); do this for all connections between battery and alternator/starter and chassis/engine.
From running alternator you should be seeing 13.5-15.5V at the battery, otherwise the battery is not being charged.
When the alternator is not running, a charged battery should be at 12.6-12.8V.
If you replaced the alternator, and all the cables show acceptable voltage drop (less than 0.3V) then you should look at the battery, is it holding a charge, does it have any dead cells, does it need replacing.
- battery negative post and engine block;
- battery positive post and alternator post;
if you see more than 0.3V across either of those, then you have to look at the cable and its connections to see if they are corroded (or otherwise have high resistance); do this for all connections between battery and alternator/starter and chassis/engine.
From running alternator you should be seeing 13.5-15.5V at the battery, otherwise the battery is not being charged.
When the alternator is not running, a charged battery should be at 12.6-12.8V.
If you replaced the alternator, and all the cables show acceptable voltage drop (less than 0.3V) then you should look at the battery, is it holding a charge, does it have any dead cells, does it need replacing.
could be multiple reasons for failure...
possibly not enough amperage output causing extra stress on it making it suck down the voltage...
it could just be overheating as well...which would cause a voltage drop
does your alternator have a plasic shroud on it??? it should....its used for cooling the alternator..
some options are to buy a higher amp alternator, or switch to a different one completely..
when I changed from the stock PCM to my Holley EFI system, I had alternator issues...
I tried a resistor, I tried a light bulb...
what finally fixed my issues very similar to what you are seeing... is I bought a one wire alternator from powerbastards.com
its a 220 amp alternator, with a self exciter in it....no need to connect a wire to the 4 wire connector...
solved all my problems....might be a good solution for you as well.
only catch with a one wire alternator is that if the vehicle is going to sit for any real length of time, it will drain your battery..so I always recommend wiring in a high current relay or a fuse you can pull if you have to park the car for more than a week or two at a time.
possibly not enough amperage output causing extra stress on it making it suck down the voltage...
it could just be overheating as well...which would cause a voltage drop
does your alternator have a plasic shroud on it??? it should....its used for cooling the alternator..
some options are to buy a higher amp alternator, or switch to a different one completely..
when I changed from the stock PCM to my Holley EFI system, I had alternator issues...
I tried a resistor, I tried a light bulb...
what finally fixed my issues very similar to what you are seeing... is I bought a one wire alternator from powerbastards.com
its a 220 amp alternator, with a self exciter in it....no need to connect a wire to the 4 wire connector...
solved all my problems....might be a good solution for you as well.
only catch with a one wire alternator is that if the vehicle is going to sit for any real length of time, it will drain your battery..so I always recommend wiring in a high current relay or a fuse you can pull if you have to park the car for more than a week or two at a time.
Thread Starter
TECH Apprentice
Joined: Sep 2011
Posts: 344
Likes: 1
From: La Porte, TX
Sorry for my late reply(again) lol but I finally fixed my problems. I threw a 03 Cadillac escalade 145a alternator on it and also rewired the excitor wire and also put a new connector on the wire that connects to the back of the alternator and now I'm getting 13v+, I have yet to see it go under 13.... We'll see tomorrow on my commute to school and work if it really did fix it.
Thread Starter
TECH Apprentice
Joined: Sep 2011
Posts: 344
Likes: 1
From: La Porte, TX
I quadruple checked all the connections and they all check out good. The only thing I wasn't ok with was the positive wire connector that connects to the the back of the alternator, several of the wires were severed and the connector was loose. So I cut and stripped a new part of the wire and threw a new connector on it to be sure it was making a solid connection. I also soldered the new excitor wire pigtail to the existing excitor wire that I had previously ripped out of the old pigtail.
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