My truck has dual alternators.

This weekend I noticed the FMP, Ficm Main Power, on my Torque App went down to 12v for a few seconds. It is usually around 13-13.5. I am guessing one or both of the alternators are going.

How can one tell which alternator is going bad in a dual alternator truck?

I am assuming it is the alternator. Can it be something else, like a bad battery?

I thought as long as the engine is running the alternator should put out voltage, even if the battery was unhooked?

 

Take them off and get them load tested..

 

really though, if one is in fact bad, I would go a head and replace both of them if it were me..

 

Is there no way to test them on the truck? There are no Alternator shops around here and I would have to take it to Advance Auto and I would not trust those people with checking the plastic wheels on the Big Wheel I had as a kid.

http://originalbigwheel.us/images/SpinoutRacer500.jpg

 

I agree with ya there.... I'm not aware of away myself, but there might be.. I'm sure someone will chime in here soon.. But I took mine off the truck and got it tested when I replaced my FICM from ED.. That way if something happened to my FICM I had documentation for my warranty, and I found that mine was indeed bad, so I replaced my alternator also...

 

If you have a DC clamp on amp meter you can
put it on each one and see the output in amps.

Never unhook an alternator when the thing is running.
It tosses one BIG spike that can damage/kill things.

The best way is the hardest way with a 2 alternator system.

But if you do have the DC meter be sure to zero it out with
the truck off and have the coil facing the fight direction or the
numbers will show up negative. An alternator that is working will
have a positive output where one that is bad/dead might be lower
or negative output. One other thing to do is place a volt meter in
the AC mode and look at the voltage. That will be AC ripple and you
don't want much if any.
http://content.amprobe.com/appnotes/...ct_appnote.pdf

Or


BTW you think pulling a dual system would be bad how about this guy.




It may be all out front but having to do it that many times

Can't find much (well nothing) on in vehicle testing of a dual system.


Sean

6.0L Tech Folder

 

A simple way to check without removing the alternators is to unplug the exciter plug on one alternator, start the motor, turn on headlights (loads the alternator) and check the charging voltage on the other alternator at the battery. Should be about 13 to 13.5 VDC. Do the same to the other alternator. If one is bad, the charging voltages will be different with the same load.

Ed

 

I started her up this evening when I got home.

Battery voltage was 12.6x before I did anything, after sitting over night. This tells me the alternators are charging the batteries and the batteries are good.

koeo voltage dropped to 11.47, all exterior lights, including headlights, and glow plugs on.

koer the voltage went up to 12.xx

Once the glow plugs turned off, a couple minutes after starting, the voltage went up to 13.7 and climbed to 14.12.

The above measurements were at the passengers side battery terminals.

I checked the Torque app to compare numbers. Battery terminals read 14.12 with my Fluke meter. FMP read 13.0, FLP read 13.5 and VBatt read 13.6. Can the obdii port measurements be up to an entire volt off? Reference the high and low voltages on the gauges, they are about .5-1v lower from what I measured at the battery terminal.

FICM was 47.5 when I snapped the photo but was 47 at lowest and 48 at highest, typical readings for me. It did drop down to 46 when the gauges showed 12v yesterday on the way home, after about 3 hours of towing. I am guessing the battery terminals were at 13 when that happened and not really at 12, based on my testing today.

So, what do you think? It seems alternators are ok, batteries are good and a ficm may be in the future, but within spec for now.

I did not check for codes yet. I will get IDS out later tonight or tomorrow.

 

With active command on the IDS you should be able to turn one of
the alternators off and see if the other is holding or not. At least I think you can


Sean

6.0L Tech Folder

 

Being as my ficm voltage seems a bit lower than optimal I was reading the ficm repair pdf in the tech folder. It seems like a simple repair, just reflow some joints. Should I just do it or wait until the voltage drops a bit more?

I am heavily experienced with pcbs and solder, I used to design and etch my own boards for my animated Christmas Light Addiction but still build my own kits. I own Do It Yourself Christmas

I also hooked up IDS this morning and could not find anything referencing alternators except checking for ripple. I also chekced the Mode 9 Vehicle Info and found the tcm, pcm and ficm calibration.

 

You look in "Active Command" ?


Sean

6.0L Tech Folder

 

Not sure where "active command" is. I clicked every tab and checked every menu I could find.

 

Here you go


EDIT : He has a good list of IDS training videos that are well worth watching.

Sean

6.0L Tech Folder

 

Thanks Sean. That is a tricky interface. I would think they could make a better interface for the amount of money IDS costs.

I will try to get to it in the next few days.

 

I think that the guys that use it day in and day out still have to look
things up every not and then.


Sean

6.0L Tech Folder