Advice on new Alternator not working
Thread Starter
Cruising
Joined: Nov 2011
Posts: 12
Likes: 1
From: Kyle Texas
Advice on new Alternator not working
My 2002 c5 Z06 went dead as we where driving it the other night. I took out the alternator and took it to O'Reilly. They tested it and said it was dead and they gave me a new one under warranty. I charge the battery and put it in and took it on a test drive and it started to loose voltage around 10 miles and just barely made it back home. I tested the battery and it tested at 12 volts and cranks up perfect. I took the new alternator back to OReilly and they tested it on their machine and said it was fine. I put it back on and tested the battery again and then started the car and tested the new alternator and on idle it was 11.90. Sometimes a little higher sometimes a little lower.
Do you think this is just not a strong alternator?
Should I just go get a different from another auto store and try theirs?
Do you think this is just not a strong alternator?
Should I just go get a different from another auto store and try theirs?
Thread Starter
Cruising
Joined: Nov 2011
Posts: 12
Likes: 1
From: Kyle Texas
I have the battery in the tender to make sure it is fully charged. If anyone has instructions on how to do a voltage drop check on a c5 I would appreciate it. Have to run to a game, but will perform it later.
Melting Slicks
Joined: Sep 2021
Posts: 2,555
Likes: 1,213
My 2002 c5 Z06 went dead as we where driving it the other night. I took out the alternator and took it to O'Reilly. They tested it and said it was dead and they gave me a new one under warranty. I charge the battery and put it in and took it on a test drive and it started to loose voltage around 10 miles and just barely made it back home. I tested the battery and it tested at 12 volts and cranks up perfect. I took the new alternator back to OReilly and they tested it on their machine and said it was fine. I put it back on and tested the battery again and then started the car and tested the new alternator and on idle it was 11.90. Sometimes a little higher sometimes a little lower.
Do you think this is just not a strong alternator?
Should I just go get a different from another auto store and try theirs?
Do you think this is just not a strong alternator?
Should I just go get a different from another auto store and try theirs?
Thread Starter
Cruising
Joined: Nov 2011
Posts: 12
Likes: 1
From: Kyle Texas
Okay, I set my multimeter to dc 20 and I am getting something like 5.xx when going from positive on the battery to the wire on the back of the alternator. This seems like a problem. Just to be clear it is 0 from negative of the battery to the top part of the alternator.
Also, the battery was 12.9 when nothing was on before I started this test.
Also, the battery was 12.9 when nothing was on before I started this test.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,644
Likes: 4,082
From: Cape Coral, Florida
Over 5 volt voltage drop check ??…you normally see 0.2-0.4 on positive and negative side of charging circuit… I don’t remember from the video but I run a car at 2500 RPM with electrical loads such as high beams, blower motor, AC, and window defogger on and then measure…if you are seeing over 5 volts on the positive side that is like your alternator putting out 14 volts but the battery is only charging at 9 volts…a 5 volt difference…the B+ cable on the alternator runs down to the starter solenoid and the positive cable from your battery is also attached there…you will need to get underneath the car and remove both cables and clean and reattach….you should also clean the alternator B+ and the battery positive cable also.
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Michael S. Palmer
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,644
Likes: 4,082
From: Cape Coral, Florida
Okay, I set my multimeter to dc 20 and I am getting something like 5.xx when going from positive on the battery to the wire on the back of the alternator. This seems like a problem. Just to be clear it is 0 from negative of the battery to the top part of the alternator.
Also, the battery was 12.9 when nothing was on before I started this test.
Also, the battery was 12.9 when nothing was on before I started this test.
At 12.9 you probably had the battery on a charger.
