AH64ID

Let's talk alternators

10 posts in this topic

So I am pretty sure my alternator died. 

I left for work this morning and noticed the headlights were a bit dim. I assumed it was frost on the lenses so I fired up the high beams/fogs and it got dimmer. I then noticed voltage was holding about 11.4 at the ECM (from my touch). I gave it a mile or two to see if maybe it was low batteries and the voltage never came up so I turned around. 

When I got home I separated the batteries, hoping to find one bad one, and both were at 11.3ish. Then I disconnected the alternator wire and fired the truck back up. With a voltmeter the alternator output started at 9v and dropped to 6v just holding the volt meter on it. 

I also put a 10A charger on the batteries for about 10 minutes and the voltage came up to 11.6 so it appears the batteries will accept amperage but the alternator isn't supplying any. 

I never got a charge light or CEL... does anyone know the threshold for a charge light?

I will do a continuity check of the fuseable link when I get home tonight. 

I had the alternator checked out in Nov of '13 and the brushes/bearing were replaced. I was told it was very rare for the windings to fail. It only has 30K miles on it since then, but maybe a new armature brush contact is needed??

Thoughts?

Anything else I can check? 


 

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why not just take it in and have it tested?

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No reason other than time right now.... 

 

But it is an option at some point. 

Edited by AH64ID

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1 hour ago, AH64ID said:

So I am pretty sure my alternator died. 


Then I disconnected the alternator wire and fired the truck back up. With a voltmeter the alternator output started at 9v and dropped to 6v just holding the volt meter on it. 


Anything else I can check? 

 

 

A couple of thoughts: 

 

  *  What happened to the alternator 30,000 miles ago that it needed brushes and bearings? 

 

  *  Disconnecting the alternator output wire and then running the engine is never a good idea.  The field circuit for the alternator is controlled by the ECM and could easily damage the ECM.

 

Before you remove the alternator you can inspect the alternator output wiring and fusible link as you mentioned, as well as inspecting the ground circuit and the field wire to the ECM.  You could use a jumper lead from the alternator case to a battery ground as a test to bypass a potential ground circuit problem.

 

- John

Edited by Tractorman

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2 hours ago, Tractorman said:

A couple of thoughts: 

 

  *  What happened to the alternator 30,000 miles ago that it needed brushes and bearings? 

 

  *  Disconnecting the alternator output wire and then running the engine is never a good idea.  The field circuit for the alternator is controlled by the ECM and could easily damage the ECM.

 

Before you remove the alternator you can inspect the alternator output wiring and fusible link as you mentioned, as well as inspecting the ground circuit and the field wire to the ECM.  You could use a jumper lead from the alternator case to a battery ground as a test to bypass a potential ground circuit problem.

 

- John

 

Engine was out so I had the alternator freshened up. Nothing was wrong with it. 

 

The field circuit is controlled by the ECM but there shouldn't by any additional feedback to the ECM with the alternator output disconnected. 

 

The ground circuit seemed fine this morning. 

 

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Well there is a new development. 

I was getting ready to move it around to the shop and park it so with it running I started wiggling the connection from the ECM and got my voltage back! 

It didn't stay back but the alternator is able to output power when I am applying sideways pressure to the connection. I tried wiggling wires and pushing them in and it didn't work, the only way to get power was to either push up or down on the connection. 

Thoughts on that? I am guessing I have a loose connection in the alternator side, which means the rebuild kit from Geno's should fix it.

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