The other day my van was acting up while on a trip. I have an Edge Insight CTS monitor and noticed that the voltage was jumping all over the place from 12.3V to 14.1V. I have two house batteries that i know are bad I didn't realize this until getting to camp and then finding them dead the next day. I can usually get about 48 hours of continuous use before they are due for a charge. So upon seeing the Alternator act up I figured that my house batteries roached one or both of my alternators. Oddly enough the alternator put out a steady 13.5V at idle, but as soon as you give any throttle it cut out completely.

So today I decided to dig in a try to figure out which alternator was the problem one. I started the van and everything was charging as usual. I couldn't get it replicate the issue. So I disconnected the top alternator and then started the van, NO charging voltage. I then switched them to double check that the bottom was the issue. NO voltage again! Reconnected both and it spits 13.5-14V.

THEN, I cleaned the battery terminals and hooked everyhting back up. NOTHING! No voltage from the alternators at all.... I am so damn confused with the dual alternator system on these vans. You would think that if one alternator craps out the other will pick up the slack, but it appears that if one goes, they both go.

Can anyone shed some light on how this system works? Is there a good way to test each alternator independently?

Your wisdom is much appreciated.

 

Hi there Ty. I can relate to the challenge of troubleshooting dual alternators on the rig. Mine is set up the same. You can use your phone as a scanner, with Forscan Lite or Torque Pro, and a wireless OBDII dongle, and read the codes - you will see a code telling you which alternator is not putting out.

P1105 Dual Alternaotr Upper fault detected
P1106 Dual Alternator Lower fault detected

I'd say start with your batteries and make sure they are 100%, then check battery cables and cable grounds for good tight connections. Wiring on these trucks is now suspect.

Attached is a pdf troubleshooting guild that might help.

If the alternators are not making noise (bearings), and just not producing voltage, it's probably the voltage regulator brushes that have worn out, or the voltage regulators. They get changed out as a unit. I just changed out the voltage regulator/brush set on my lower alt, and am getting ready to do the same to the upper alt. It's not a bad process.

Here's a link to what I worked through on mine:
https://www.ford-trucks.com/forums/1...l#post19350642

 

Thank you for this! That document was the key. I poked around a bit and noticed the connector on the upper alternator was a bit loose. Pushing it down seems to have solved my issues.

Though I am still interested in learning how these vans operate both alternators. I find it odd that it wouldn't recognize a lack of voltage from one and default to full voltage with the other. It seems like the system isn't set up for redundancy, which feels a bit counter productive with an ambulance.

Either way, I'll make sure to carry the tools to do a parking lot swap if one fails.

Thanks again!

 

Hi Ty.... Also PNW'r, Van'r, 7.3'r......


I have a dual alt F350, Ambulance package.

I don't remember the specifics, but the dual alternators were not designed or installed for redundancy.
IIRC, All 7.3 were originally single alt. Ford saw the huge load of glow plugs and starting was overworking the electrical system during recovery, leading to some sort of failures.
Some vehicles were deemed high load, and granted dual alternators for recovery.
The alternators are ECU controlled. There is a method to the recharge procedure. One alternator supplements the other to reduce load on the primary.

Thats all I remember.

 

Took this from the Ford Service Manual. I am still looking for more information and will post up anything useful I find.

EDIT: I was only able to find a small section on "Inspection and Verification" beyond what was posted above as the symptom and pinpoint tests.