2006 F350 with 50K miles showing low volts 11.6-11.8. Yesterday indicated all was fine. Showed low volts for first time last night. Wiggled all the cables and checked the alternator connections. Restarted and gauge read 13.6. Now again today, 11.6- 11.8V. I'm guessing possibly alternator unless someone knows of something to check I may not be aware of. I'm going to clean all the battery terminals tomorrow but before I pull the alternator wanted to know if anyone had any other ideas. Batteries are both 6 month old OEM.

Thanks for any input.

 

The two wire connector at the alternator can go bad and lose connection. This would cause the alternator to stop charging. If wiggling that connector causes voltage changes, then that might worth replacing before you go to an alternator.

Remember that the alternator will not start charging until the glow plugs finish their cycle, which can last up to two minutes after key on. So don't let that fool you.

 

Thanks David. The low voltage reading is constant so I will check that connector tomorrow before pulling the alternator to have it tested.

 

It is normal, when the glow plugs are on for voltage to read 11.6 to 11.8.
When you turn the key on, the glow plugs turn on.
When the glow plugs are on, the alternator is prevented from
outputing voltage.
Depending upon the ambient temp and the temp of the engine,
the glow plugs might stay on for up to 2 minutes.
The "wait to start lite" on the dash does NOT indicate when the
glow plugs are on.

When I start my 6.0, I wait for the voltage to go to 13.8 to 14.1 before
I drive off. Once warmed up, when I re-start the voltage hits 13.8 right
away.

 

Is the 6.0 really supposed to do this? Seems counter productive to not allow the charging system to do its work upon start up, considering when you're starting ,(even if its plugged in) you're draining batteries, and then if engine starts, not allowing batteries to charge. If truck stalls you may not have enough juice to restart, if charging started right away, it could make the difference between on your way or stranded. dumb dumb dumb!

 

Yes, it REALLY is normal for the 6.0 version to do this.....

 

WHY is does it, is something that I've often wondered, and never heard anyone answer.

The glow plugs draw something on the order of 8-10 amps each, and the engine running draws 30-40 amps at idle, if I remember correctly. Those two loads alone are more than the total output of the stock alternator. So I always assumed they thought it was bad to overload the stock alternator every time you started the truck and that's why it was done.

I have no evidence to that though, and there may very well be a better reason.

 

Ok if the glow plugs draw that much amperage, and the engine draws that much amperage, I'd want the alt working right away, to supply what ever it can to the batteries, seems stupid to allow all amperage drawn from the batteries without recharging them asap. As well can't the engine sense when its running and tell the glow plugs to trun off?

 

I'm sure the engine computer knows when the engine is running. The glow plugs are on for up to 2 minutes, depending on coolant and oil temperature.

I'm pretty sure that the engineers that designed the engine had a good reason for doing what they did. If I ever meet any of them, I'll ask them.

 

PLEASE DO!

 

Factually false.

1 wire is the sense wire, which is the way the alternator detects the voltage at the battery and adjust charging voltage accordingly.

If this wire is broken / making poor contact, it will result in an OVER VOLTAGE condition and to OVER charge, not stop charging.

The other wire is the exciter wire.

If this wire is broken / not making contact, it will result in little / less / no current / voltage.


It is possible to have,

A) Sense wire circuit bad

B) Exciter wire circuit bad (which will light the Alternator light)

C) Both bad.

And any combination / permutation of the above intermittently.


Voltage change from wiggling the connector may indicate fault in any of the above, or in the connector at the alternator, or in the harness further away.

Or it may indicate no more fault than just a dirty connector that can be fixed with a good cleaning and greasing with dielectric grease.

If it is at the alternator, the only way to repair a bad alternator connector is to replace the alternator unless you are a rebuilder.

If it is the harness.... it is the harness.

 

Good to hear from you Gearloose! What changed? Why ya back?

 

OK. Took the alternator off and had it tested. PASSED. Auto part store says alternator is fine. I know when the glow plugs shut off, it sends a signal to the alt to let it begin its charge. Is there a fuse or relay I should be looking at?

Thanks,

 

With the truck running, after the glow plugs have shut off, check for power on both of the wires at the connector to the alternator.

 

Should there be 12v on each of them? I'm going to have to charge the batteries first. They're to the point that they're struggling to turn it over.