alternator ??

joe_mnDecember 1, 2009

96 caddy. dash can display digital voltage readings. start car, 13.8V. drive a mile and it drops to 11V. come to stop and it might go up to 13.5 again. belt is tight. all battery connections have been cleaned. been doing this for 2-3 weeks. car starts fine. today i drove 5 miles and it went to 11.2, than 10.9, than 9.9 and got low voltage message. got off road and car died. won't crank. left it and will check it tomorrow. now, should i jump it and let donor car charge it for 1/2 hr or so and head for home or take out battery and bring it home and charge it for 3-4 hrs?

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the charging system is not working. Main suspect is the alternator, but could be something else.

Take the battery home and charge it.
Install in stranded car.
Use a jump start to preserve as much charge in the battery as possible.
Drive to service shop. Changing an alternator and other diagnostics alongside a road is no fun and may be dangerous.

If the first attempt at fixing the problem fails, at least the car will be inside a building where you can tackle the problem. At my location, the weather is changing from nice to cold and naughty.

    Bookmark   December 1, 2009 at 11:23PM
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i agree charging at home is better. if i had a fully charged new battery, how long do you think i could drive with no headlights or extra draw items?

    Bookmark   December 1, 2009 at 11:42PM
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got battery. only have 6amp charger. charged it for 4hrs. started at 4amps and never seemed to vary. jumped car and it started at 14.4v. drove 2 miles and still was 14.4. than it started to go down. 12ish or so. than 11.7. occasionally would go up to 14 but than back down to 11.5. got home and it was 11.1. 10mile trip. put charger on and it seemed to have poor connection. i took off positive cable. its a double stack on this car. redid spacer washer and now charger says 6amps. will charge for awhile than go for drive. want to load test battery first.

    Bookmark   December 2, 2009 at 3:19PM
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You likely have corrosion causing a voltage drop. The alternator could easily be charging, its just the voltage drop isn't letting the power being produced to flow.

Now where is that voltage drop? Hmmmmmm.......

I could silver bullet this, and have about an 80% chance of being accurate. But the right way, the way auto technicians have to do this is test and measure for it and then once they locate it, repair it and then they can prove they fixed the car without risking driving out on the road just to experience a breakdown.,

Take a good voltmeter and connect it from the positive post of the battery (The cable bolt if necessary) and the other lead connect it to the alternator output terminal. Start the car and turn on a bunch of accessories. (Rear defogger, blower motor on high, headlights) Read the voltage between the alternator output terminal and the battery positive post. Now move the lead from the battery positive post and connect it at the under-hood fuse block main connection.

Next connect the voltmeter to the case of the alternator, and the other lead of the voltmeter to the negative battery post connection (bolt). Again measure the voltage with the engine running, and a bunch of accessories turned on.

Was any of those measurements more than .4-.5v? Which one?

If so know what to do next?

    Bookmark   December 3, 2009 at 10:42AM
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A prime suspect is the alternator, and John_g has given you insructions for checking out voltage drops.

You've got a '96 Caddy, but you did not say how many miles or if this was the original alternator. I am assuming it is the orignal alternator.

It appears to put out charge for a moment and then quits. Its not charging most of the time. This suggests that the brushes (on slip rings in the alternator) are worn out or hung up in the holders. That may be all that is wrong.

    Bookmark   December 3, 2009 at 7:42PM
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i have more time than money. i suspected worn brushes several weeks ago so i took out alternator and checked brushes. at least 1/2 material was left. cleaned holder. no difference. so i put in used alternator yesterday. yes, i know a used unit is probably just as prone to failure or have issues but it is running fine now. 14v at start, 13.5-8 with lights on. $25 is nice but we will see how long it lasts.

    Bookmark   December 5, 2009 at 1:47PM
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dropped again. you drive for 30 min or so and all of a sudden it drops to 12 than 11 or so. i had motor out 2yrs ago and kinked up ground cable for battery. it measured a bit high but my vom is shaky. cable is a dual lead. $65 at napa. i got a nice used one at junkyard. drove it for 1/2 hr and it stays at 13.3 with lights on. lights off, it jumps to 13.6 or so. so i got rid of my 13yr old alt and now have a 13yr old replacement.

    Bookmark   December 6, 2009 at 5:29PM
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You needed to do the volt drop testing when the system voltage started falling.

"Silver Bullet". The ground cable attaches to a stud and nut right above the starter. The stud and engine block corrode each other from dissimilar metals contacting and being exposed to the elements. So even though the cable may be tight, it is as if it isn't really connected to the engine block. The fix includes completely removing the bolt and running a tap in the threads. Wire wheel the stud to shine it up and then reinstall. You can add additional grounding straps at other locations if you want to. The problem with the silver bullet approach is it only works when the ground cable stud is really losing its connection as the block heats up. Testing while its acting up before going through all of the effort to clean up the connection proves whether or not it is the problem. Simply attempting this fix, without proving it is necessary first could easily result in you posting back telling us, " That wasn't it. You cleaned the stud and nut, but the problem is still there".

    Bookmark   December 6, 2009 at 10:13PM
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the ground cable is 15" long. my car has a cast bracket on the front side of the block for attaching the torque dogbone. newer caddys dont have the dogbone setup. the threaded bolt is double nutted. the top nut like to seize and than turn out the stud so the ground strap will wrap itself around the stud. thats how i chewed it up last year when i pulled the motor. the car at the boneyard had been picked over and the bracket was gone. the stud was just laying on the battery tray. thought about picking it up but just took the ground cable.

    Bookmark   December 7, 2009 at 10:21AM
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Bump. Bringing this post to the forefront for Joe_mn.

    Bookmark   April 2, 2010 at 2:54AM
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