alt problem??
Posting Guru
Joined: Jul 2004
Posts: 1,777
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From: Buckingham, IA
I'm not familiar with the dual alt. setup so just basic diagnostic procedures. I would disconnect the large wire from which ever alt. is easier to get to to prevent back feeding from one to the other. (There is possibly a regulator to prevent this during normal operation.) Start the engine and check the voltage at the large lug on each alt. If there is low voltage from only one, replace that one. If low voltage from both, replace the cheapest one first to see if that gives some charge.
Senior User
Joined: Sep 2004
Posts: 329
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From: Carroll County, MD
I guess (but not sure) that you might be able to test one alt at a time by disconnecting it from the system (large battery lead and small plug, sealing each one up well) and then run the truck and see if the voltage does anything.
By the same token (and also not sure on this) you might be able to disconnect the lower in this method, and replace just the upper, and get around for a while.
Just thoughts
EDIT: Beat me to it Farmdad
By the same token (and also not sure on this) you might be able to disconnect the lower in this method, and replace just the upper, and get around for a while.
Just thoughts
EDIT: Beat me to it Farmdad
Senior User
Joined: Sep 2004
Posts: 329
Likes: 0
From: Carroll County, MD
It was standard as part of the Ambo Prep Package, but could be ordered by itself - I think it was for winches and such that are power hungry.
I don't know if there is an isolation device between the two alts so that one won't drain into the other if either goes bad...
I don't know if there is an isolation device between the two alts so that one won't drain into the other if either goes bad...
Thread Starter
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Senior User
Joined: Nov 2005
Posts: 138
Likes: 1
From: Buchanan,MI
to check batteries do i need to disconnect the leads from one of the 2 batts? dont know if they are hooked together. after all the starts and restarts the batts are low. now it wont crank so its time for the charger.......
Junior User
Joined: Feb 2004
Posts: 61
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From: Michigan
You do need to unhook one lead from one of the batteries to check them. Beware of the quick testers for testing them though. Mine both tested good at a local chain part store and after a starter and cable change took them both out for the long test on the machine inside, they both tested bad several hundred dollars after the initial "good" test.
Junior User
Joined: Feb 2004
Posts: 61
Likes: 0
From: Michigan
The service manual for my 99 shows the dual generator option and both alternators are controlled by the PCM on the schematic. If the pcm don't send a voltage to the pin (labeled I in the schematic at alternator), the alternator won't output a voltage so it may have to be taken off to test at the local parts store. Assuming it is telling both to charge may or may not be true. The top one is a 5 minute removal assuming your belt tensioner has the same 3/8" hole to pull it back with a long rachet and easily slide the belt off. Just did mine a week ago. Had a local shop rebuild it for 75$ and back up and running same day. Seems the regulator/rectifier went bad but he also did brushes and bearings. Both alternators have exact schematic layouts so the price difference must be in mounting differences and lack of demand for the second lower unit. The internals appear to be the same for a rebuild if you have a shop that will do it. I'll cross my fingers for you!
Last edited by kb8pgc; Jan 16, 2008 at 01:47 AM.
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Gone, but not forgotten
Joined: Oct 2005
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From: Charlotte-Fairbanks-Bflo
I'm surprised nobody's pointed out that the alternator's have zilch to do with the running of the gp's beyond keeping the batteries up to snuff so they are capable of doing so.
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Senior User
Joined: Nov 2005
Posts: 138
Likes: 1
From: Buchanan,MI
tested top alt.....BAD new one installed in 10 min. alls good..
gonna take bottom one off after trip and check out and rebuilt. im assuming its bad too. mechanic said id be fine for now if not forever. as long as im not running a bunch of trailer batteries charging,accessories,welder,etc.......
gonna take bottom one off after trip and check out and rebuilt. im assuming its bad too. mechanic said id be fine for now if not forever. as long as im not running a bunch of trailer batteries charging,accessories,welder,etc.......
Laughing Gas
Joined: Jul 2003
Posts: 1,157
Likes: 1
From: Littleton, Colorado
All you'd have to do to test the bottom one is disconnect the fat positive cable off the top one and read your voltage at the battery if below 13-15V then it would be time for a new one.
If it is bad, it will cause the top one to work more and heat it up. That will cause it to fail prematurely.
I would at least charge your batteries completely with a charger first. The reason so many alt. fail is people think that its the alt job to charge up a deeply discharged battery. It is not. It is to top off the charge of a battery in good condition and to run all the electrical devices in the vehicle. A lot of folks get in a maintanence nightmare between batteries and alt. Bad batts ruin alts and vice versa. With batteries at $100 ea and alt at $200, it adds up fast.
It would be a ten minute job to check it and know for sure. Your call.
Austin
If it is bad, it will cause the top one to work more and heat it up. That will cause it to fail prematurely.
I would at least charge your batteries completely with a charger first. The reason so many alt. fail is people think that its the alt job to charge up a deeply discharged battery. It is not. It is to top off the charge of a battery in good condition and to run all the electrical devices in the vehicle. A lot of folks get in a maintanence nightmare between batteries and alt. Bad batts ruin alts and vice versa. With batteries at $100 ea and alt at $200, it adds up fast.
It would be a ten minute job to check it and know for sure. Your call.
Austin