Let's talk alternators....

[AH64ID]

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?

 

[kthaxton]

If the wiring to the alternator appears to be ok, my next step would just be to take it into an auto parts store and have it tested...but it does sound like it is the alternator to me. My only other thought is the charging circuit within the PCM, but I doubt that.

 

[AH64ID]

Yeah that's where I am at. I might be able to pull it tonight and test it tomorrow.

The ECM is commanding a voltage of 15.xx so that appeared normal.

At least the rebuild kits from Geno's are cheap and appear to be genuine bosch.

 

[PWong]

So I am pretty sure my alternator died.


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'm sure your alternator is dead.
The open circuit voltage should be much much higher, may be over 40V.

 

[phantomusa]

I would also pull both battery's and the alternator nd have them all checked at the same time

 

[AH64ID]

Batteries are 6.5 years old and have been showing signs of getting weaker. They are on the chopping block anyhow.



I am hoping it's rebuildable.

 

[DavidC]

Why doesn't anyone recommend checking the sensor under the Drivers side battery before removing and testing the Alternator ?.

Dave

 

[phantomusa]

Isn't that under the battery temp sensor only to monitor the battery for overcharging

 

[DavidC]

Isn't that under the battery temp sensor only to monitor the battery for overcharging

Monitors battery temp for charging so it is in the mix.

Dave

 

[MichaelOverfield]

It sure sounds like a bad alternator. Let us know when you figure it out.

 

[AH64ID]

It helps determine the desired charge voltage but if my desired voltage is 15.xx and I am at 11.xx it's not the battery temp sensor.

The battery temp sensor was reading correctly this morning as well.

 

[DavidC]

OPERATION
The amount of DC current produced by the generator
is controlled by EVR circuitry contained within
the PCM. This circuitry is connected in series with
the generators second rotor field terminal and its
ground.
Voltage is regulated by cycling the ground path to
control the strength of the rotor magnetic field. The
EVR circuitry monitors system line voltage and battery
temperature (refer to Battery Temperature Sensor
for more information). It then compensates and
regulates generator current output accordingly. Also
refer to Charging System Operation for additional
information.

Dave

 

[DavidC]

Maybe the diode pack.

Dave

 

[Motorhead]

John, Just for curiosity, How many miles on the truck/alternator? I usually find the slip ring brushes have worn out.

 

[AH64ID]

126K on the alternator, but only 30K since it was freshened up with new brushes and bearings.

The fuseable link has good continuity and the batteries are taking a charge from my 10A charger. The alternator just isn't putting out enough amperage, so hopefully it's the brushes as they seem to be the cheapest fix.

 

[Motorhead]

Unless the slip rings are real rough, they shouldn't wear that fast.

 

[AH64ID]

No they shouldn't. I guess I'll know when I get it pulled. It may be a bit thou as I don't have the time right now to do much with it and need it able to move under its own power.

 

[AH64ID]

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 (spiked to 16.5 )!

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.

 

[Motorhead]

I would rather find a good O.E. used than to buy a "Marx Brothers" rebuild at the big box auto parts stores. Every "Rebuilt" anything I have seen has had some kind of problem, sub-standard workmanship or cheap junky parts installed. I did a major on my neighbors 1992 first gen and I rebuilt his own alternator. I did have to buy a replacement rotor for the alternator but I as able to find an O.E. quality replacement. I also rebuilt his starter completely and he said it had never turned the engine over so fast.

 

[AH64ID]

If I have to replace the whole thing I am considering the 180A OEM alternator from the 6.7, but with what I just found I am fairly certain it's an easy fix.